text:
Journal of Animal Ecology
[SJR: 3.359] [H-I: 119] [56 followers] Follow
Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0021-8790 - ISSN (Online) 1365-2656
Published by John Wiley and Sons [1612 journals]
- Intra-specific priority effects modify compensatory responses to changes
in hatching phenology in an amphibian
- Authors: Andrea P. Murillo-Rincón; Nora A. Kolter, Anssi Laurila, Germán Orizaola
Abstract: 1.In seasonal environments, modifications in the phenology of life-history events can alter the strength of time-constraints experienced by organisms. Offspring can compensate for a change in timing of hatching by modifying their growth and development trajectories. However, intra- and inter -specific interactions may affect these compensatory responses, in particular if differences in phenology between cohorts lead to significant priority effects (i.e. the competitive advantage that early hatching individuals have over late hatching ones).2.Here, we conducted a factorial experiment to determine if intra-specific priority effects can alter compensatory phenotypic responses to hatching delay in a synchronic breeder by rearing moor frog (Rana arvalis) tadpoles in different combinations of phenological delay and food abundance.3.Tadpoles compensated for the hatching delay by speeding up their development, but only when reared in groups of individuals with identical hatching phenology. In mixed-phenology groups, strong competitive effects by non-delayed tadpoles prevented the compensatory responses, and delayed larvae metamorphosed later than in single phenology treatments. Non-delayed individuals gained advantage from developing with delayed larvae by increasing their developmental and growth rates as compared to single phenology groups.4.Food shortage prolonged larval period and reduced mass at metamorphosis in all treatments, but it did not prevent compensatory developmental responses in larvae reared in single phenology groups.5.This study demonstrates that strong intra-specific priority effects can constrain the compensatory growth and developmental responses to phenological change, and that priority effects can be an important factor explaining the maintenance of synchronic life-histories (i.e. explosive breeding) in seasonal environments.This article is protected by copyright. All rights reserved.
PubDate: 2016-11-28T07:00:28.154774-05:
- Authors: Andrea P. Murillo-Rincón; Nora A. Kolter, Anssi Laurila, Germán Orizaola
- Precipitation alters interactions in a grassland ecological community
- Authors: Nicolas Deguines; Justin S. Brashares, Laura R. Prugh
Abstract: 1.Climate change is transforming precipitation regimes worldwide. Changes in precipitation regimes are known to have powerful effects on plant productivity, but the consequences of these shifts for the dynamics of ecological communities are poorly understood. This knowledge gap hinders our ability to anticipate and mitigate the impacts of climate change on biodiversity.2.Precipitation may affect fauna through direct effects on physiology, behavior or demography, through plant-mediated indirect effects, or by modifying interactions among species. In this paper, we examined the response of a semi-arid ecological community to a fivefold change in precipitation over seven years.3.We examined the effects of precipitation on the dynamics of a grassland ecosystem in central California from 2007 to 2013. We conducted vegetation surveys, pitfall trapping of invertebrates, visual surveys of lizards, and capture-mark-recapture surveys of rodents on 30 plots each year. We used structural equation modelling to evaluate the direct, indirect, and modifying effects of precipitation on plants, ants, beetles, orthopterans, kangaroo rats, ground squirrels, and lizards.4.We found pervasive effects of precipitation on the ecological community. Although precipitation increased plant biomass, direct effects on fauna were often stronger than plant-mediated effects. In addition, precipitation altered the sign or strength of consumer-resource and facilitative interactions among the faunal community such that negative or neutral interactions became positive or vice versa with increasing precipitation.5.These findings indicate that precipitation influences ecological communities in multiple ways beyond its recognized effects on primary productivity. Stochastic variation in precipitation may weaken the average strength of biotic interactions over time, thereby increasing ecosystem stability and resilience to climate change.This article is protected by copyright. All rights reserved.
PubDate: 2016-11-27T04:05:22.854633-05:
- Authors: Nicolas Deguines; Justin S. Brashares, Laura R. Prugh
- Earlier nesting by generalist predatory bird is associated with human
responses to climate change
- Authors: Shawn H. Smith; Karen Steenhof, Christopher J.W. McClure, Julie A. Heath
Abstract: Warming temperatures cause temporal changes in growing seasons and prey abundance that drive earlier breeding by birds, especially dietary specialists within homogeneous habitat. Less is known about how generalists respond to climate-associated shifts in growing seasons or prey phenology, which may occur at different rates across land cover types.We studied whether breeding phenology of a generalist predator, the American kestrel (Falco sparverius), was associated with shifts in growing seasons and, presumably, prey abundance, in a mosaic of non-irrigated shrub/grasslands and irrigated crops/pastures. We examined the relationship between remotely-sensed normalized difference vegetation index (NDVI) and abundance of small mammals that, with insects, constitute approximately 93% of kestrel diet biomass. We used NDVI to estimate the start of the growing season (SoGS) in irrigated and non-irrigated lands from 1992 to 2015 and tested whether either estimate of annual SoGS predicted the timing of kestrel nesting. Finally, we examined relationships among irrigated SoGS, weather and crop planting.NDVI was a useful proxy for kestrel prey because it predicted small mammal abundance and past studies showed that NDVI predicts insect abundance. NDVI-estimated SoGS advanced significantly in irrigated lands (β = −1·09 ± 0·30 SE) but not in non-irrigated lands (β = −0·57 ± 0·53). Average date of kestrel nesting advanced 15 days in the past 24 years and was positively associated with the SoGS in irrigated lands, but not the SoGS in non-irrigated lands. Advanced SoGS in irrigated lands was related to earlier planting of crops after relatively warm winters, which were more common in recent years.Despite different patterns of SoGS change between land cover types, kestrel nesting phenology shifted with earlier prey availability in irrigated lands. Kestrels may preferentially track prey in irrigated lands over non-irrigated lands because of higher quality prey on irrigated lands, or earlier prey abundance may release former constraints on other selective pressures to breed early, such as seasonal declines in fecundity or competition for high-quality mates.This is one of the first examples of an association between human adaptation to climate change and shifts in breeding phenology of wildlife.American kestrels, inhabiting a mosaic of habitats, nested earlier in response to earlier prey availability in agriculture, but not wildlands. Prey in agriculture were earlier because farmers planted crops earlier following warmer winters. This suggests an association between human adaptation to climate change and shifts in breeding phenology of wildlife.
PubDate: 2016-11-21T19:00:02.552334-05:
- Authors: Shawn H. Smith; Karen Steenhof, Christopher J.W. McClure, Julie A. Heath
- Temporal shifts and temperature sensitivity of avian spring migratory
phenology: A phylogenetic meta-analysis
- Authors: T Usui; S H M Butchart, A B Phillimore
Abstract: 1.There are wide reports of advances in the timing of spring migration of birds over time and in relation to rising temperatures, though phenological responses vary substantially within and among species. An understanding of the ecological, life-history and geographic variables that predict this intra- and inter-specific variation can guide our projections of how populations and species are likely to respond to future climate change.2.Here, we conduct phylogenetic meta-analyses addressing slope estimates of the timing of avian spring migration regressed on (i) year and (ii) temperature, representing a total of 413 species across five continents. We take into account slope estimation error and examine phylogenetic, ecological and geographic predictors of intra- and inter-specific variation.3.We confirm earlier findings that on average birds have significantly advanced their spring migration time by 2.1 days decade−1 and 1.2 days °C−1. We find that over time and in response to warmer spring conditions short-distance migrants have advanced spring migratory phenology by more than long-distance migrants. We also find that larger bodied species show greater advance over time compared to smaller bodied species. Our results did not reveal any evidence that interspecific variation in migration response is predictable on the basis of species' habitat or diet.4.We detected a substantial phylogenetic signal in migration time in response to both year and temperature, suggesting that some of the shifts in migratory phenological response to climate are predictable on the basis of phylogeny. However, we estimate high levels of species and spatial variance relative to phylogenetic variance, which is consistent with plasticity in response to climate evolving fairly rapidly and being more influenced by adaptation to current local climate than by common descent.5.On average, avian spring migration times have advanced over time and as spring has become warmer. While we are able to identify predictors that explain some of the true among-species variation in response, substantial intra- and inter-specific variation in migratory response remains to be explained.This article is protected by copyright. All rights reserved.
PubDate: 2016-11-18T11:45:21.644962-05:
- Authors: T Usui; S H M Butchart, A B Phillimore
- Seal mothers expend more on offspring under favourable conditions and less
when resources are limited
- Authors: Clive R. McMahon; Robert G. Harcourt, Harry R. Burton, Owen Daniel, Mark A. Hindell
Abstract: 1.In mammals, maternal expenditure on offspring is a complex mix of several factors including the species' mating system, offspring sex and the condition and age of the mother. While theory suggests that in polygynous species mothers should wean larger male offspring than females when resources and maternal conditions allow, the evidence for this remains equivocal.2.Southern elephant seals are highly dimorphic, polygynous capital breeders existing in an environment with highly variable resources and should therefore provide clear evidence to support the theoretical expectations of differential maternal expenditure in male and female pups.3.We quantified maternal size (mass and length) and pup size at birth and weaning for 342 elephant seal mothers at Macquarie Island. The study was conducted over 11 years of contrasting sea-ice and Southern Annular Mode values, both indices of maternal prey resources.4.Overall, large females weaned male pups that weighed 17 kg (15.5%) more than female pups. Maternal condition varied by as much as 59 kg among years, and was positively related to SAM, and negatively to maximum sea-ice extent. Smaller mothers weaned relatively larger male pups under favourable conditions, this effect was less apparent for larger mothers.5.We developed a simple model linking environmental variation to maternal masses post-partum, followed by maternal masses post-partum to weaning masses and then weaning masses to pup survival and demonstrated that environmental conditions affected predicted survival so that the pups of small mothers had an estimated 7% increase in first year survival in "good" vs "bad" years compared to 1% for female pups of large mothers.6.Co-occurrence of environmental quality and conservative reproductive tactics suggests that mothers retain substantial plasticity in maternal care, enhancing their lifetime reproductive success by adjusting reproductive expenditure relative to both prevailing environmental conditions and their own capabilities.This article is protected by copyright. All rights reserved.
PubDate: 2016-11-18T11:45:19.211547-05:
- Authors: Clive R. McMahon; Robert G. Harcourt, Harry R. Burton, Owen Daniel, Mark A. Hindell
- Correlational selection on personality and social plasticity: morphology
and social context determine behavioural effects on mating success
- Authors: Pierre-Olivier Montiglio; Tina W Wey, Ann T Chang, Sean Fogarty, Andrew Sih
Abstract: 1.Despite a central line of research aimed at quantifying relationships between mating success and sexually dimorphic traits (e.g., ornaments), individual variation in sexually selected traits often explains only a modest portion of the variation in mating success.2.Another line of research suggests that a significant portion of the variation in mating success observed in animal populations could be explained by correlational selection, where the fitness advantage of a given trait depends on other components of an individual's phenotype and/or its environment. We tested the hypothesis that interactions between multiple traits within an individual (phenotype-dependence) or between an individual's phenotype and its social environment (context-dependence) can select for individual differences in behaviour (i.e., personality) and social plasticity.3.To quantify the importance of phenotype- and context-dependent selection on mating success, we repeatedly measured the behaviour, social environment, and mating success of about 300 male stream water striders, Aquarius remigis. Rather than explaining individual differences in long-term mating success, we instead quantified how the combination of a male's phenotype interacted with the immediate social context to explain variation in hour-by-hour mating decisions. We suggest that this analysis captures more of the mechanisms leading to differences in mating success.4.Males differed consistently in activity, aggressiveness, and social plasticity. The mating advantage of these behavioural traits depended on male morphology and varied with the number of rival males in the pool, suggesting mechanisms selecting for consistent differences in behaviour and social plasticity. Accounting for phenotype- and context-dependence improved the amount of variation in male mating success we explained statistically by 30 – 274%.5.Our analysis of the determinants of male mating success provides important insights into the evolutionary forces that shape phenotypic variation. In particular, our results suggest that sexual selection is likely to favour individual differences in behaviour, social plasticity (i.e. individuals adjusting their behaviour), niche preference (i.e. individuals dispersing to particular social conditions), or social niche construction (i.e. individuals modifying the social environment). The true effect of sexual traits can only be understood in interaction with the individual's phenotype and environment.This article is protected by copyright. All rights reserved.
PubDate: 2016-11-18T07:30:24.708458-05:
- Authors: Pierre-Olivier Montiglio; Tina W Wey, Ann T Chang, Sean Fogarty, Andrew Sih
- Does movement behaviour predict population densities' A test with 25
butterfly species
- Authors: Cheryl B. Schultz; B. Guy Pe'er, Christine Damiani, Leone Brown, Elizabeth E. Crone
Abstract: Diffusion, which approximates a correlated random walk, has been used by ecologists to describe movement, and forms the basis for many theoretical models. However, it is often criticized as too simple a model to describe animal movement in real populations.We test a key prediction of diffusion models, namely, that animals should be more abundant in land cover classes through which they move more slowly. This relationship between density and diffusion has rarely been tested across multiple species within a given landscape.We estimated diffusion rates and corresponding densities of 25 Israeli butterfly species from flight path data and visual surveys. The data were collected across 19 sites in heterogeneous landscapes with four land cover classes: semi-natural habitat, olive groves, wheat fields, and field margins.As expected from theory, species tended to have higher densities in land cover classes through which they moved more slowly and lower densities in land cover classes through which they moved more quickly. Two components of movement (move length and turning angle) were not associated with density, nor was expected net squared displacement. Move time, however, was associated with density, and animals spent more time per move step in areas with higher density.The broad association we document between movement behaviour and density suggests that diffusion is a good first approximation of movement in butterflies. Moreover, our analyses demonstrate that dispersal is not a species-invariant trait, but rather one that depends on landscape context. Thus land cover classes with high diffusion rates are likely to have low densities and be effective conduits for movement.This article is protected by copyright. All rights reserved.
PubDate: 2016-11-17T07:15:29.741457-05:
- Authors: Cheryl B. Schultz; B. Guy Pe'er, Christine Damiani, Leone Brown, Elizabeth E. Crone
- Climatic conditions cause spatially dynamic polygyny thresholds in a large
- Authors: Jeffrey A. Manning; Philip D. McLoughlin
Abstract: 1.The polygyny threshold (PT) is a critical transition point in the sexual selection process for many organisms in natural populations, characterizing when females choose to mate with an already mated male over an unmated one to improve fitness. Understanding its causes and consequences is therefore of high interest. While both theoretical and empirical work suggest that the degree of polygyny within a species is plastic and a function of male inequality, the functional relationship between underlying availability of resources occupied by breeding males under variable climatic conditions and the dynamics of PTs across space and time has received less attention.2. Here, we use a standardized measure of male mating inequality as the culmination of female mate choices to analyze how spatially dynamic PTs in a naturally regulated feral horse (Equus ferus caballus) population emerge along a geographic gradient in a known, limiting resource (freshwater) each year from variable climatic conditions. PT distance from permanent freshwater increased with increasing precipitation during the breeding season of each year, suggesting a relationship between annual resource availability and female mate choice.3. The mechanism by which climatic conditions underpin the spatial dynamics of PTs was likely through precipitation providing ephemeral freshwater sources across the study area that effectively weakened the gradient in availability of permanent freshwater, thereby providing mating males that occupied home ranges far from permanent water with access to this limiting resource and enabling them to attract and retain females. Increased precipitation also coincided with a decreased proportion of males in the population that experienced sexual selection pressure attributed to female mate choice in relation to the acquisition and/or defense of freshwater sources.4. Climatic conditions caused spatial shifts in PTs annually along the geographic gradient in resource availability. Our findings reveal that such environmental gradients may either buffer or amplify impacts of climatic variation on selection pressure operating in natural populations, and emphasize the importance of integrating spatially explicit PTs with atmospheric fluctuations when predicting the effect of climatic change on selection processes within populations that occupy environmental gradients.This article is protected by copyright. All rights reserved.
PubDate: 2016-11-15T06:11:01.965019-05:
- Authors: Jeffrey A. Manning; Philip D. McLoughlin
- Sexual selection can both increase and decrease extinction probability:
reconciling demographic and evolutionary factors
- Authors: Carlos Martínez-Ruiz; Robert J. Knell
Abstract: Previous theoretical models of the effect of sexual selection on average individual fitness in a population have mostly predicted that sexually selected populations should adapt faster and clear deleterious mutations more quickly than populations where sexual selection is not operating.While some laboratory studies have supported these predictions, others have not and studies of field systems have tended to find negative effects of sexual selection, or no effect. The negative effects of sexual selection found in field and other studies are usually ascribed to the costs associated with strong sexual selection acting on the population.Here, using an individual-based model that allows feedback between demographic and evolutionary processes, we find that sexual selection can lead to both increases and decreases in population-level fitness measures such as extinction probability and adaptation rate. Whether fitness increases or decreases depends on a variety of environmental and demographic factors including the nature of environmental change, the carrying capacity of the environment, the average fecundity of the population in question and the strength of condition dependence.In many cases, our model predicts that sexual selection leads to higher extinction probability in small populations because of an increased risk of demographic stochasticity, but lower extinction probability in larger populations because of faster adaptation rates. This is consistent with field studies that have mostly focussed on very small populations such as recently introduced birds, and tend to find negative effects, and also with laboratory studies that tend to use larger populations and have tended to find positive effects.These findings go at least some way towards an understanding of the apparent contradictions between theoretical predictions, laboratory studies and field data.Choosy females and males with bright or loud displays can change how a population responds to environmental stress. Large populations are made more resilient to stress, but small populations are more vulnerable.
PubDate: 2016-11-14T04:35:36.152994-05:
- Authors: Carlos Martínez-Ruiz; Robert J. Knell
- Sensitivity of UK butterflies to local climatic extremes: which life
stages are most at risk'
- Authors: Osgur McDermott Long; Rachel Warren, Jeff Price, Tom M. Brereton, Marc S. Botham, Aldina M. A. Franco
Abstract: There is growing recognition as to the importance of extreme climatic events (ECEs) in determining changes in species populations. In fact, it is often the extent of climate variability that determines a population's ability to persist at a given site.This study examined the impact of ECEs on the resident UK butterfly species (n = 41) over a 37-year period. The study investigated the sensitivity of butterflies to four extremes (drought, extreme precipitation, extreme heat and extreme cold), identified at the site level, across each species' life stages. Variations in the vulnerability of butterflies at the site level were also compared based on three life-history traits (voltinism, habitat requirement and range).This is the first study to examine the effects of ECEs at the site level across all life stages of a butterfly, identifying sensitive life stages and unravelling the role life-history traits play in species sensitivity to ECEs.Butterfly population changes were found to be primarily driven by temperature extremes. Extreme heat was detrimental during overwintering periods and beneficial during adult periods and extreme cold had opposite impacts on both of these life stages. Previously undocumented detrimental effects were identified for extreme precipitation during the pupal life stage for univoltine species. Generalists were found to have significantly more negative associations with ECEs than specialists.With future projections of warmer, wetter winters and more severe weather events, UK butterflies could come under severe pressure given the findings of this study.This paper tackles a previously understudied field, addressing the impacts of extreme weather on biodiversity specifically butterflies in this study. It has used novel and dynamic approaches to identify extreme weather events which vary according to the life stage for each species and has identified some very interesting results.
PubDate: 2016-10-31T03:35:24.884581-05:
- Authors: Osgur McDermott Long; Rachel Warren, Jeff Price, Tom M. Brereton, Marc S. Botham, Aldina M. A. Franco
- Corrigendum
- PubDate: 2016-10-24T04:21:15.420102-05:
- PubDate: 2016-10-24T04:21:15.420102-05:
- Seasonal detours by soaring migrants shaped by wind regimes along the East
Atlantic Flyway
- Authors: Wouter M. G. Vansteelant; Judy Shamoun-Baranes, Willem Manen, Jan Diermen, Willem Bouten
Abstract: Avian migrants often make substantial detours between their seasonal destinations. It is likely some species do this to make the most of predictable wind regimes along their respective flyways. We test this hypothesis by studying orientation behaviour of a long-distance soaring migrant in relation to prevailing winds along the East Atlantic Flyway.We tracked 62 migratory journeys of 12 adult European Honey Buzzards Pernis apivorus with GPS loggers. Hourly fixes were annotated with local wind vectors from a global atmospheric model to determine orientation behaviours with respect to the buzzards' seasonal goal destinations. This enabled us to determine hot spots where buzzards overdrifted and overcompensated for side winds. We then determined whether winds along the buzzards' detours differed from winds prevailing elsewhere in the flyway.Honey Buzzards cross western Africa using different routes in autumn and spring. In autumn, they overcompensated for westward winds to circumvent the Atlas Mountains on the eastern side and then overdrifted with south-westward winds while crossing the Sahara. In spring, however, they frequently overcompensated for eastward winds to initiate a westward detour at the start of their journey. They later overdrifted with side winds north-westward over the Sahel and north-eastward over the Sahara, avoiding adverse winds over the central Sahara.We conclude that Honey Buzzards make seasonal detours to utilize more supportive winds further en route and thereby expend less energy while crossing the desert. Lifelong tracking studies will be helpful to elucidate how honey buzzards and other migrants learn complex routes to exploit atmospheric circulation patterns from local to synoptic scales.Many migrating birds engage in seasonal detours during migration. The authors show how a Palearctic soaring migrant initiates a detour into a headwind at the start of spring migration in anticipation of tailwinds later on in its journey.
PubDate: 2016-10-18T19:00:02.808224-05:
- Authors: Wouter M. G. Vansteelant; Judy Shamoun-Baranes, Willem Manen, Jan Diermen, Willem Bouten
- Fast-slow life history is correlated with individual differences in
movements and prey selection in an aquatic predator in the wild
- Authors: Shinnosuke Nakayama; Tobias Rapp, Robert Arlinghaus
Abstract: Fast and slow life histories are proposed to covary with consistent individual differences in behaviour, but little is known whether it holds in the wild, where individuals experience natural fluctuations of the environment.We investigated whether individual differences in behaviour, such as movement traits and prey selection, are linked to variation in life-history traits in Eurasian perch (Perca fluviatilis) in the wild.Using high-resolution acoustic telemetry, we collected the positional data of fish in a whole natural lake and estimated individual movement traits by fitting a 2-state correlated random walk model. Prey selection was inferred from stable isotope analysis using scale samples. Life-history traits were estimated by fitting a biphasic growth model to an individual growth trajectory back-calculated from scale samples.Life-history traits were correlated with behavioural traits such as movements and prey selection. Individuals with higher reproductive effort were found to switch more frequently between active and inactive modes and show greater reliance on prey from pelagic pathways (indicated by lower δ13C). Further, individuals with faster juvenile growth were found to stay active for a longer time during the adult stage.Our results demonstrate the link between individual behavioural differences and fast-slow life-history traits under ecologically relevant conditions.This article is protected by copyright. All rights reserved.
PubDate: 2016-10-17T08:21:13.050584-05:
- Authors: Shinnosuke Nakayama; Tobias Rapp, Robert Arlinghaus
- Corrigendum
- PubDate: 2016-10-17T05:07:09.786449-05:
- PubDate: 2016-10-17T05:07:09.786449-05:
- Decoupled diversity dynamics in green and brown webs during primary
succession in a salt marsh
- Authors: Maarten Schrama; Fons der Plas, Matty P. Berg, Han Olff
Abstract: 1.Terrestrial ecosystems are characterised by a strong functional connection between the green (plant-herbivore-based) and brown (detritus-detritivore-based) parts of the food web, which both develop over successional time. However, the interlinked changes in green and brown food web diversity patterns in relation to key ecosystem processes are rarely studied.2.Here, we demonstrate changes in species richness, diversity and evenness over a wide range of invertebrate green and brown trophic groups during 100 years of primary succession in a salt marsh ecosystem, using a well-calibrated chronosequence.3.We contrast two hypotheses on the relationship between green and brown food web diversity across succession: i) 'coupled diversity hypothesis', which predicts that all trophic groups covary similarly with the main drivers of successional ecosystem assembly versus ii) the 'decoupled diversity hypothesis', where green and brown trophic groups diversity respond to different drivers during succession.4.We found that, while species richness for plants and invertebrate herbivores (green web groups) both peaked at intermediate productivity and successional age, the diversity of macro-detritivores, microarthropod microbivores and secondary consumers (brown web groups) continuously increased towards the latest successional stages. These results suggest that green web trophic groups are mainly driven by vegetation parameters, such as the amount of bare soil, vegetation biomass production, and vegetation height, while brown web trophic groups are mostly driven by the production and standing stock of dead organic material and soil development.5.Our results show that plant diversity cannot simply be used as a proxy for the diversity of all other species groups that drive ecosystem functioning, as brown and green diversity components in our ecosystem responded differently to successional gradients.This article is protected by copyright. All rights reserved.
PubDate: 2016-10-14T09:26:59.595831-05:
- Authors: Maarten Schrama; Fons der Plas, Matty P. Berg, Han Olff
- Accounting for genetic differences among unknown parents in
microevolutionary studies: How to include genetic groups in quantitative
genetic animal models
- Authors: Matthew E. Wolak; Jane M. Reid
Abstract: 1.Quantifying and predicting microevolutionary responses to environmental change requires unbiased estimation of quantitative genetic parameters in wild populations. 'Animal models', which utilise pedigree data to separate genetic and environmental effects on phenotypes, provide powerful means to estimate key parameters and have revolutionised quantitative genetic analyses of wild populations.2.However, pedigrees collected in wild populations commonly contain many individuals with unknown parents. When unknown parents are non-randomly associated with genetic values for focal traits, animal model parameter estimates can be severely biased. Yet, such bias has not previously been highlighted and statistical methods designed to minimise such biases have not been implemented in evolutionary ecology.3.We first illustrate how the occurrence of non-random unknown parents in population pedigrees can substantially bias animal model predictions of breeding values and estimates of additive genetic variance, and create spurious temporal trends in predicted breeding values in the absence of local selection. We then introduce 'genetic group' methods, which were developed in agricultural science, and explain how these methods can minimise bias in quantitative genetic parameter estimates stemming from genetic heterogeneity among individuals with unknown parents.4.We summarise the conceptual foundations of genetic group animal models and provide extensive, step-by-step tutorials that demonstrate how to fit such models in a variety of software programs. Furthermore, we provide new functions in R that extend current software capabilities and provide a standardized approach across software programs to implement genetic group methods.5.Beyond simply alleviating bias, genetic group animal models can directly estimate new parameters pertaining to key biological processes. We discuss one such example, where genetic group methods potentially allow the microevolutionary consequences of local selection to be distinguished from effects of immigration and resulting gene flow.6.We highlight some remaining limitations of genetic group models and discuss opportunities for further development and application in evolutionary ecology. We suggest that genetic group methods should no longer be overlooked by evolutionary ecologists, but should become standard components of the toolkit for animal model analyses of wild population datasets.This article is protected by copyright. All rights reserved.
PubDate: 2016-10-12T05:55:43.070355-05:
- Authors: Matthew E. Wolak; Jane M. Reid
- Genetic Allee effects and their interaction with ecological Allee effects
- Authors: Meike J. Wittmann; Hanna Stuis, Dirk Metzler
Abstract: 1.It is now widely accepted that genetic processes such as inbreeding depression and loss of genetic variation can increase the extinction risk of small populations. However, it is generally unclear whether extinction risk from genetic causes gradually increases with decreasing population size or whether there is a sharp transition around a specific threshold population size. In the ecological literature, such threshold phenomena are called "strong Allee effects" and they can arise for example from mate limitation in small populations.2.In this study, we aim to a) develop a meaningful notion of a "strong genetic Allee effect", b) explore whether and under what conditions such an effect can arise from inbreeding depression due to recessive deleterious mutations, and c) quantify the interaction of potential genetic Allee effects with the well-known mate-finding Allee effect.3.We define a strong genetic Allee effect as a genetic process that causes a population's survival probability to be a sigmoid function of its initial size. The inflection point of this function defines the critical population size. To characterize survival-probability curves, we develop and analyze simple stochastic models for the ecology and genetics of small populations.4.Our results indicate that inbreeding depression can indeed cause a strong genetic Allee effect, but only if individuals carry sufficiently many deleterious mutations (lethal equivalents). Populations suffering from a genetic Allee effect often first grow, then decline as inbreeding depression sets in, and then potentially recover as deleterious mutations are purged. Critical population sizes of ecological and genetic Allee effects appear to be often additive, but even superadditive interactions are possible.5.Many published estimates for the number of lethal equivalents in birds and mammals fall in the parameter range where strong genetic Allee effects are expected. Unfortunately, extinction risk due to genetic Allee effects can easily be underestimated as populations with genetic problems often grow initially, but then crash later. Also interactions between ecological and genetic Allee effects can be strong and should not be neglected when assessing the viability of endangered or introduced populations.This article is protected by copyright. All rights reserved.
PubDate: 2016-10-12T03:51:17.911272-05:
- Authors: Meike J. Wittmann; Hanna Stuis, Dirk Metzler
- African departure rather than migration speed determines variation in
spring arrival in pied flycatchers
- Authors: J. Ouwehand; C. Both
Abstract: 1.Properly timed spring migration enhances reproduction and survival. Climate change requires organisms to respond to changes such as advanced spring phenology. Pied flycatchers Ficedula hypoleuca have become a model species to study such phenological adaptations of long-distance migratory songbirds to climate change, but data on individuals' time schedules outside the breeding season are still lacking.2.Using light-level geolocators we studied variation in migration schedules across the year in a pied flycatcher population in the Netherlands, which sheds light on the ability for individual adjustments in spring arrival timing to track environmental changes at their breeding grounds.3.We show that variation in arrival dates to breeding sites in 2014 was caused by variation in departure date from Sub-Saharan Africa, and not by environmental conditions encountered en route. Spring migration duration was short for all individuals, on average two weeks. Males migrated ahead of females in spring, while migration schedules in autumn were flexibly adjusted according to breeding duties. Individuals were therefore not consistently early or late throughout the year.4.In fast migrants like our Dutch pied flycatchers, advancement of arrival to climate change likely requires changes in spring departure dates. Adaptation for earlier arrival may be slowed down by harsh circumstances in winter, or years with high costs associated with early migration.This article is protected by copyright. All rights reserved.
PubDate: 2016-10-10T21:05:30.514229-05:
- Authors: J. Ouwehand; C. Both
- Let's stay together? Intrinsic and extrinsic factors involved in pair bond
dissolution in a recolonizing wolf population
- Authors: Cyril Milleret; Petter Wabakken, Olof Liberg, Mikael Åkesson, Øystein Flagstad, Harry Peter Andreassen, Håkan Sand
Abstract: For socially monogamous species, breeder bond dissolution has important consequences for population dynamics, but the extent to which extrinsic or intrinsic population factors causes pair dissolution remain poorly understood, especially among carnivores.Using an extensive life-history data set, a survival analysis and competing risks framework, we examined the fate of 153 different wolf (Canis lupus) pairs in the recolonizing Scandinavian wolf population, during 14 winters of snow tracking and DNA monitoring.Wolf pair dissolution was generally linked to a mortality event and was strongly affected by extrinsic (i.e. anthropogenic) causes. No divorce was observed, and among the pair dissolution where causes have been identified, death of one or both wolves was always involved. Median time from pair formation to pair dissolution was three consecutive winters (i.e. approximately 2 years). Pair dissolution was mostly human-related, primarily caused by legal control actions (36·7%), verified poaching (9·2%) and traffic-related causes (2·1%). Intrinsic factors, such as disease and age, accounted for only 7·7% of pair dissolutions. The remaining 44·3% of dissolution events were from unknown causes, but we argue that a large portion could be explained by an additional source of human-caused mortality, cryptic poaching.Extrinsic population factors, such as variables describing the geographical location of the pair, had a stronger effect on risk of pair dissolution compared to anthropogenic landscape characteristics. Population intrinsic factors, such as the inbreeding coefficient of the male pair member, had a negative effect on pair bond duration. The mechanism behind this result remains unknown, but might be explained by lower survival of inbred males or more complex inbreeding effects mediated by behaviour.Our study provides quantitative estimates of breeder bond duration in a social carnivore and highlights the effect of extrinsic (i.e. anthropogenic) and intrinsic factors (i.e. inbreeding) involved in wolf pair bond duration. Unlike the effects of intrinsic and extrinsic factors that are commonly reported on individual survival or population growth, here we provide quantitative estimates of their potential effect on the social unit of the population, the wolf pair.Few estimates of pair bond duration are available for social species, especially for carnivores. The authors found that wolf pair bond duration in Scandinavia was short (half of the dissolution events occurred after three consecutive winters), and dissolutions were mostly caused by humans. This shows the impact of extrinsic factors (i.e. humans) on the social unit of this large carnivore population.
PubDate: 2016-09-28T03:32:06.434028-05:
- Authors: Cyril Milleret; Petter Wabakken, Olof Liberg, Mikael Åkesson, Øystein Flagstad, Harry Peter Andreassen, Håkan Sand
- Forbidden fruit: human settlement and abundant fruit create an ecological
trap for an apex omnivore
- Authors: Clayton T. Lamb; Garth Mowat, Bruce N. McLellan, Scott E. Nielsen, Stan Boutin
Abstract: Habitat choice is an evolutionary product of animals experiencing increased fitness when preferentially occupying high-quality habitat. However, an ecological trap (ET) can occur when an animal is presented with novel conditions and the animal's assessment of habitat quality is poorly matched to its resulting fitness.We tested for an ET for grizzly (brown) bears using demographic and movement data collected in an area with rich food resources and concentrated human settlement.We derived measures of habitat attractiveness from occurrence models of bear food resources and estimated demographic parameters using DNA mark–recapture information collected over 8 years (2006–2013). We then paired this information with grizzly bear mortality records to investigate kill and movement rates.Our results demonstrate that a valley high in both berry resources and human density was more attractive than surrounding areas, and bears occupying this region faced 17% lower apparent survival. Despite lower fitness, we detected a net flow of bears into the ET, which contributed to a study-wide population decline.This work highlights the presence and pervasiveness of an ET for an apex omnivore that lacks the evolutionary cues, under human-induced rapid ecological change, to assess trade-offs between food resources and human-caused mortality, which results in maladaptive habitat selection.The authors tested for an ecological trap (ET) in south-east British Columbia where human settlement and rich grizzly bear habitat overlap. Bears occupying the ET faced survival consequences, which produced source–sink dynamics with far-reaching effects. To date, this is the most rigorous test of an ET for a large mammal.
PubDate: 2016-09-28T00:00:02.394242-05:
- Authors: Clayton T. Lamb; Garth Mowat, Bruce N. McLellan, Scott E. Nielsen, Stan Boutin
- Symbionts modify interactions between insects and natural enemies in the
- Authors: Jan Hrček; Ailsa H. C. McLean, H. Charles J. Godfray
Abstract: Eukaryotes commonly host communities of heritable symbiotic bacteria, many of which are not essential for their hosts' survival and reproduction. There is laboratory evidence that these facultative symbionts can provide useful adaptations, such as increased resistance to natural enemies. However, we do not know how symbionts affect host fitness when the latter are subject to attack by a natural suite of parasites and pathogens.Here, we test whether two protective symbionts, Regiella insecticola and Hamiltonella defensa, increase the fitness of their host, the pea aphid (Acyrthosiphon pisum), under natural conditions.We placed experimental populations of two pea aphid lines, each with and without symbionts, in five wet meadow sites to expose them to a natural assembly of enemy species. The aphids were then retrieved and mortality from parasitoids, fungal pathogens and other causes assessed.We found that both Regiella and Hamiltonella reduce the proportion of aphids killed by the specific natural enemies against which they have been shown to protect in laboratory and cage experiments. However, this advantage was nullified (Hamiltonella) or reversed (Regiella) by an increase in mortality from other natural enemies and by the cost of carrying the symbiont. Symbionts therefore affect community structure by altering the relative success of different natural enemies.Our results show that protective symbionts are not necessarily advantageous to their hosts, and may even behave more like parasites than mutualists. Nevertheless, bacterial symbionts may play an important role in determining food web structure and dynamics.Protective effects of microbial symbionts are known from laboratory studies, but little is known about how they affect host fitness in the field. The authors show that protective symbiosis does work in nature and can affect food web structure and dynamics. However, symbionts do not necessarily increase host fitness.
PubDate: 2016-09-26T04:45:29.670625-05:
- Authors: Jan Hrček; Ailsa H. C. McLean, H. Charles J. Godfray
- Masculinized females produce heavier offspring in a group living rodent
- Authors: Loreto A. Correa; Cecilia León, Juan Ramírez-Estrada, Mauricio Soto-Gamboa, Roger D. Sepúlveda, Luis A. Ebensperger
Abstract: Alternative morphotypes have been reported less frequently in females than in males. An exception to this rule is the gradient of phenotypical masculinization reported in some female mammals, in which feminized and masculinized females represent two opposite ends along this gradient. These phenotypical differences originate during prenatal development as the consequence of maternal effects. Feminized and masculinized females differ in several traits, including morphological, physiological, behavioural and reproductive traits.Differences previously reported in reproductive traits between feminized and masculinized females come mostly from mechanistic studies performed in the laboratory, and not necessarily on social species. As a result, it is unclear to what extent these reported differences between female alternative morphotypes materialize in wild, natural populations.We quantified the effect of female alternative morphotype on female reproductive traits in a natural population of Octodon degus, a highly social rodent. We assessed female alternative morphotype through a continuous gradient of anogenital distance. Thus, feminized females were close to the short end of anogenital distance, while masculinized females were close to the long end of this gradient. We also tested the hypothesis that the social environment interacts with female morphotype to influence female reproductive traits.In female degus, only body weight affected litter size, where heavier females weaned more offspring. Masculinized females delivered male-biased litters and weaned heavier offspring. Lastly, masculinized females gave birth later in the breeding season compared to feminized females.Contrary to previous claims, our findings do not support that masculinized females are less fertile than feminized females. Moreover, masculinized females produced heavier, potentially higher quality offspring compared with feminized females.Fertility did not differ between masculinized and feminized females and that masculinized females made a higher maternal investment during lactation, implying that masculinization does not significantly impair female reproductive performance as has been previously suggested. While the authors cannot currently posit that masculinized females are a superior morphotype, they can at least hypothesize that masculinized females are not a 'pathological/suboptimum' morphotype.
PubDate: 2016-09-26T04:45:26.33359-05:0
- Authors: Loreto A. Correa; Cecilia León, Juan Ramírez-Estrada, Mauricio Soto-Gamboa, Roger D. Sepúlveda, Luis A. Ebensperger
- Injecting epidemiology into population viability analysis: avian cholera
transmission dynamics at an arctic seabird colony
- Authors: Samuel A. Iverson; H. Grant Gilchrist, Catherine Soos, Isabel I. Buttler, N. Jane Harms, Mark R. Forbes
Abstract: Infectious diseases have the potential to spread rapidly and cause high mortality within populations of immunologically naïve hosts. The recent appearance of avian cholera, a highly virulent disease of birds caused by the bacterium Pasteurella multocida, at remote Arctic seabird colonies is an emerging conservation concern.Determining disease risk to population viability requires a quantitative understanding of transmission potential and the factors that regulate epidemic persistence. Estimates of the basic (R0) and real-time (Rt) reproductive number are critical in this regard – enumerating the number of secondary infections caused by each primary infection in a newly invaded host population and the decline in transmission rate as susceptible individuals are removed via mortality or immunized recovery.Here, we use data collected at a closely monitored common eider (Somateria mollissima) breeding colony located in the Canadian Arctic to examine transmission and host population dynamics. Specifically, we infer epidemic curves from daily mortality observations and use a likelihood-based procedure to estimate changes in the reproductive number over a series of annual outbreaks. These data are interpreted in relation to concurrent changes in host numbers to assess local extinction risk.Consistent with expectations for a novel pathogen invasion, case incidence increased exponentially during the initial wave of exposure (R0 = 2·5; generation time = 6·5 days ± 1·1 SD). Disease conditions gradually abated, but only after several years of smouldering infection (Rt ≈ 1). In total, 6194 eider deaths were recorded during outbreaks spanning eight consecutive breeding seasons. Breeding pair abundance declined by 56% from the pre-outbreak peak; however, a robust population of >4000 pairs remained intact upon epidemic fade-out. Overall, outbreak patterns were consistent with herd immunity acting as a mitigating factor governing in the extent and duration of mortality.Disease mortality is frequently modelled as a form of stochastic catastrophe in wildlife population assessments, whereas our approach gives shape to the functional response between transmission and host population dynamics. We conclude that increased emphasis on integrating epidemiological and population processes is essential to predicting the conservation impact of emerging infectious diseases in wildlife.Emerging infectious diseases are a growing concern in wildlife conservation. This paper uses innovative methods developed for the real-time study of disease epidemics in humans and applies them to an Arctic seabird species experiencing a new series of highly virulent outbreaks of avian cholera to predict disease dynamics and assess the threat to population viability.
PubDate: 2016-09-20T10:45:26.833225-05:
- Authors: Samuel A. Iverson; H. Grant Gilchrist, Catherine Soos, Isabel I. Buttler, N. Jane Harms, Mark R. Forbes
- How individual Montagu's Harriers cope with Moreau's Paradox during the
Sahelian winter
- Authors: Almut Ellinor Schlaich; Raymond H. G. Klaassen, Willem Bouten, Vincent Bretagnolle, Ben Johannes Koks, Alexandre Villers, Christiaan Both
Abstract: Hundreds of millions of Afro-Palaearctic migrants winter in the Sahel, a semi-arid belt south of the Sahara desert, where they experience deteriorating ecological conditions during their overwintering stay and have to prepare for spring migration when conditions are worst. This well-known phenomenon was first described by R.E. Moreau and is known ever since as Moreau's Paradox. However, empirical evidence of the deteriorating seasonal ecological conditions is limited and little is known on how birds respond.Montagu's Harriers Circus pygargus spend 6 months of the year in their wintering areas in the Sahel. Within the wintering season, birds move gradually to the south, visiting several distinct sites to which they are site-faithful in consecutive years. At the last wintering site, birds find themselves at the southern edge of the Sahelian zone and have no other options than facing deteriorating conditions.We tracked 36 Montagu's Harriers with GPS trackers to study their habitat use and behaviour during winter and collected data on the abundance of their main prey, grasshoppers, in Senegal. Since grasshopper abundance was positively related to vegetation greenness (measured as normalized difference vegetation index, NDVI), we used NDVI values as a proxy for prey abundance in areas where no field data were collected. Prey abundance (grasshopper counts and vegetation greenness) at wintering sites of Montagu's Harriers decreased during the wintering period.Montagu's Harriers responded to decreasing food availability by increasing their flight time during the second half of the winter. Individuals increased flight time more in areas with stronger declines in NDVI values, suggesting that lower food abundance required more intense foraging to achieve energy requirements. The apparent consequence was that Montagu's Harriers departed later in spring when their final wintering site had lower NDVI values and presumably lower food abundance and consequently arrived later at their breeding site.Our results confirmed the suggestions Moreau made 40 years ago: the late wintering period might be a bottleneck during the annual cycle with possible carry-over effects to the breeding season. Ongoing climate change with less rainfall in the Sahel region paired with increased human pressure on natural and agricultural habitats resulting in degradation and desertification is likely to make this period more demanding, which may negatively impact populations of migratory birds using the Sahel.Migrant birds wintering in the Sahel need to prepare for spring migration in dry conditions. GPS tracking of Montagu's Harriers shows that individuals increase their foraging effort in response to decreasing food availability. Individuals departed later from drier areas, suggesting carry-over effects of winter to breeding.
PubDate: 2016-09-19T00:00:02.094751-05:
- Authors: Almut Ellinor Schlaich; Raymond H. G. Klaassen, Willem Bouten, Vincent Bretagnolle, Ben Johannes Koks, Alexandre Villers, Christiaan Both
- Modeling effects of nonbreeders on population growth estimates
- Authors: Aline M. Lee; Jane M. Reid, Steven R. Beissinger
Abstract: 1.Adult individuals that do not breed in a given year occur in a wide range of natural populations. However, such nonbreeders are often ignored in theoretical and empirical population studies, limiting our knowledge of how nonbreeders affect realized and estimated population dynamics and potentially impeding projection of deterministic and stochastic population growth rates.2.We present and analyze a general modeling framework for systems where breeders and nonbreeders differ in key demographic rates, incorporating different forms of nonbreeding, different life histories, and frequency-dependent effects of nonbreeders on demographic rates of breeders.3.Comparisons of estimates of deterministic population growth rate, λ, and demographic variance, σ2d, from models with and without distinct nonbreeder classes show that models that do not explicitly incorporate nonbreeders give upwardly biased estimates of σ2d, particularly when the equilibrium ratio of nonbreeders to breeders, N*nb/N*b, is high. Estimates of λ from empirical observations of breeders only are substantially inflated when individuals frequently re-enter the breeding population after periods of nonbreeding.4.Sensitivity analyses of diverse parameterizations of our model framework, with and without negative frequency-dependent effects of nonbreeders on breeder demographic rates, show how changes in demographic rates of breeders versus nonbreeders differentially affect λ. In particular, λ is most sensitive to nonbreeder parameters in long-lived species, when N*nb/N*b > 0, and when individuals are unlikely to breed at several consecutive time steps.5.Our results demonstrate that failing to account for nonbreeders in population studies can obscure low population growth rates that should cause management concern. Quantifying the size and demography of the nonbreeding section of populations and modeling appropriate demographic structuring is therefore essential to evaluate nonbreeders' influence on deterministic and stochastic population dynamics.This article is protected by copyright. All rights reserved.
PubDate: 2016-09-14T04:50:57.949622-05:
- Authors: Aline M. Lee; Jane M. Reid, Steven R. Beissinger
- Intra-specific competition, not predation, drives lizard tail loss on
- Authors: Yuval Itescu; Rachel Schwarz, Shai Meiri, Panayiotis Pafilis
Abstract: Tail autotomy is mainly considered an anti-predator mechanism. Theory suggests predation pressure relaxes on islands, subsequently reducing autotomy rates. Intra-specific aggression, which may also cause tail loss, probably intensifies on islands due to the higher abundance. We studied whether tail autotomy is mostly affected by predation pressure or by intra-specific competition. We further studied whether predator abundance or predator richness is more important in this context.To test our predictions we examined multiple populations of two gecko species: Kotschy's gecko (Mediodactylus kotschyi; mainland and 41 islands) and the Mediterranean house gecko (Hemidactylus turcicus; mainland and 17 islands), and estimated their abundances together with five indices of predation.In both species autotomy rates are higher on islands and decline with most predation indices, in contrast with common wisdom, and increase with gecko abundance. In M. kotschyi tail loss rates are higher on predator and viper-free islands, but increase with viper abundance. We suggest that autotomy is not simply, or maybe even mainly, an anti-predatory mechanism. Rather, such defense mechanisms are a response to complex direct and indirect biotic interactions and perhaps, in the case of tail autotomy in insular populations, chiefly to intra-specific aggression.This article is protected by copyright. All rights reserved.
PubDate: 2016-09-14T02:10:31.070689-05:
- Authors: Yuval Itescu; Rachel Schwarz, Shai Meiri, Panayiotis Pafilis
- Interspecific interference competition at the resource patch scale: do
large herbivores spatially avoid elephants while accessing water?
- Authors: Nicolas Ferry; Stéphane Dray, Hervé Fritz, Marion Valeix
Abstract: Animals may anticipate and try to avoid, at some costs, physical encounters with other competitors. This may ultimately impact their foraging distribution and intake rates. Such cryptic interference competition is difficult to measure in the field, and extremely little is known at the interspecific level.We tested the hypothesis that smaller species avoid larger ones because of potential costs of interference competition and hence expected them to segregate from larger competitors at the scale of a resource patch. We assessed fine-scale spatial segregation patterns between three African herbivore species (zebra Equus quagga, kudu Tragelaphus strepsiceros and giraffe Giraffa camelopardalis) and a megaherbivore, the African elephant Loxodonta africana, at the scale of water resource patches in the semi-arid ecosystem of Hwange National Park, Zimbabwe.Nine waterholes were monitored every two weeks during the dry season of a drought year, and observational scans of the spatial distribution of all herbivores were performed every 15 min. We developed a methodological approach to analyse such fine-scale spatial data.Elephants increasingly used waterholes as the dry season progressed, as did the probability of co-occurrence and agonistic interaction with elephants for the three study species. All three species segregated from elephants at the beginning of the dry season, suggesting a spatial avoidance of elephants and the existence of costs of being close to them. However, contrarily to our expectations, herbivores did not segregate from elephants the rest of the dry season but tended to increasingly aggregate with elephants as the dry season progressed.We discuss these surprising results and the existence of a trade-off between avoidance of interspecific interference competition and other potential factors such as access to quality water, which may have relative associated costs that change with the time of the year.Developing a new methodological approach, the authors show how spatial patterns of animal distributions at a resource-patch scale provide useful insights into the potential costs of interspecific interference competition. Considering a large temporal window in a seasonal ecosystem, the authors suggest mechanisms which are likely to be important for animal communities functioning.
PubDate: 2016-09-13T04:21:34.683371-05:
- Authors: Nicolas Ferry; Stéphane Dray, Hervé Fritz, Marion Valeix
- Nematode parasite diversity in birds: the role of host ecology, life
history and migration
- Authors: Tommy L. F. Leung; Janet Koprivnikar
Abstract: Previous studies have found that migratory birds generally have a more diverse array of pathogens such as parasites, as well as higher intensities of infection. However, it is not clear whether this is driven by the metabolic and physiological demands of migration, differential selection on host life-history traits or basic ecological differences between migratory and non-migratory species.Parasitic helminths can cause significant pathology in their hosts, and many are trophically transmitted such that host diet and habitat use play key roles in the acquisition of infections. Given the concurrent changes in avian habitats and migratory behaviour, it is critical to understand the degree to which host ecology influences their parasite communities.We examined nematode parasite diversity in 153 species of Anseriformes (water birds) and Accipitriformes (predatory birds) in relation to their migratory behaviour, diet, habitat use, geographic distribution and life history using previously published data.Overall, migrators, host species with wide geographic distributions and those utilizing multiple aquatic habitats had greater nematode richness (number of species), and birds with large clutches harboured more diverse nematode fauna with respect to number of superfamilies. Separate analyses for each host order found similar results related to distribution, habitat use and migration; however, herbivorous water birds played host to a less diverse nematode community compared to those that consume some animals.Birds using multiple aquatic habitats have a more diverse nematode fauna relative to primarily terrestrial species, likely because there is greater opportunity for contact with parasite infectious stages and/or consumption of infected hosts. As such, omnivorous and carnivorous birds using aquatic habitats may be more affected by environmental changes that alter their diet and range. Even though there were no overall differences in their ecology and life history compared with non-migrators, migratory bird species still harboured a more diverse array of nematodes, suggesting that this behaviour places unique demands on these hosts and warrants further study.The authors provide the first large-scale demonstration of the greater challenge by macroparasites for migratory birds regardless of their ecology and life history, as well as host species with large geographic distributions, multiple aquatic habitat use, and animal consumption. These might be more affected by anthropogenic changes altering diet and range.
PubDate: 2016-09-12T10:30:35.713153-05:
- Authors: Tommy L. F. Leung; Janet Koprivnikar
- Geographic variation and trade-offs in parasitoid virulence
- Authors: Lisa Fors; Robert Markus, Ulrich Theopold, Lars Ericson, Peter A. Hambäck
Abstract: Host–parasitoid systems are characterized by a continuous development of new defence strategies in hosts and counter-defence mechanisms in parasitoids. This co-evolutionary arms race makes host–parasitoid systems excellent for understanding trade-offs in host use caused by evolutionary changes in host immune responses and parasitoid virulence. However, knowledge obtained from natural host–parasitoid systems on such trade-offs is still limited.In this study, the aim was to examine trade-offs in parasitoid virulence in Asecodes parviclava (Hymenoptera: Eulophidae) when attacking three closely related beetles: Galerucella pusilla, Galerucella calmariensis and Galerucella tenella (Coleoptera: Chrysomelidae). A second aim was to examine whether geographic variation in parasitoid infectivity or host immune response could explain differences in parasitism rate between northern and southern sites.More specifically, we wanted to examine whether the capacity to infect host larvae differed depending on the previous host species of the parasitoids and if such differences were connected to differences in the induction of host immune systems. This was achieved by combining controlled parasitism experiments with cytological studies of infected larvae.Our results reveal that parasitism success in A. parviclava differs both depending on previous and current host species, with a higher virulence when attacking larvae of the same species as the previous host. Virulence was in general high for parasitoids from G. pusilla and low for parasitoids from G. calmariensis. At the same time, G. pusilla larvae had the strongest immune response and G. calmariensis the weakest. These observations were linked to changes in the larval hemocyte composition, showing changes in cell types important for the encapsulation process in individuals infected by more or less virulent parasitoids.These findings suggest ongoing evolution in parasitoid virulence and host immune response, making the system a strong candidate for further studies on host race formation and speciation.This study examines trade-offs in parasitoid virulence in a hymenopteran attacking three closely related beetles, revealing a higher parasitism success when infecting larvae of the same species as the previous host. These observations are linked to changes in the larval hemocyte composition when infected by more or less virulent parasitoids.
PubDate: 2016-09-12T05:41:01.167228-05:
- Authors: Lisa Fors; Robert Markus, Ulrich Theopold, Lars Ericson, Peter A. Hambäck
- Cascading effects of defaunation on the coexistence of two specialized
insect seed predators
- Authors: Guille Peguero; Helene C. Muller-Landau, Patrick A. Jansen, S. Joseph Wright
Abstract: Identification of the mechanisms enabling stable coexistence of species with similar resource requirements is a central challenge in ecology. Such coexistence can be facilitated by species at higher trophic levels through complex multi-trophic interactions, a mechanism that could be compromised by ongoing defaunation.We investigated cascading effects of defaunation on Pachymerus cardo and Speciomerus giganteus, the specialized insect seed predators of the Neotropical palm Attalea butyracea, testing the hypothesis that vertebrate frugivores and granivores facilitate their coexistence.Lab experiments showed that the two seed parasitoid species differed strongly in their reproductive ecology. Pachymerus produced many small eggs that it deposited exclusively on the fruit exocarp (exterior). Speciomerus produced few large eggs that it deposited exclusively on the endocarp, which is normally exposed only after a vertebrate handles the fruit. When eggs of the two species were deposited on the same fruit, Pachymerus triumphed only when it had a long head start, and the loser always succumbed to intraguild predation.We collected field data on the fates of 6569 Attalea seeds across sites in central Panama with contrasting degrees of defaunation and wide variation in the abundance of vertebrate frugivores and granivores. Speciomerus dominated where vertebrate communities were intact, whereas Pachymerus dominated in defaunated sites. Variation in the relative abundance of Speciomerus across all 84 sampling sites was strongly positively related with the proportion of seeds attacked by rodents, an indicator of local vertebrate abundance.Synthesis: We show that two species of insect seed predators relying on the same host plant species are niche differentiated in their reproductive strategies such that one species has the advantage when fruits are handled promptly by vertebrates and the other when they aren't. Defaunation disrupts this mediating influence of vertebrates and strongly favors one species at the expense of the other, providing a case study of the cascading effects of defaunation and its potential to disrupt coexistence of non-target species, including the hyperdiverse phytophagous insects of tropical forests.This article is protected by copyright. All rights reserved.
PubDate: 2016-09-09T11:01:40.388212-05:
- Authors: Guille Peguero; Helene C. Muller-Landau, Patrick A. Jansen, S. Joseph Wright
- Patterns of age-related change in reproductive effort differ in the
pre-natal and post-natal periods in a long-lived mammal
- Authors: John T. Paterson; Jay J. Rotella, Jennifer M. Mannas, Robert A. Garrott
Abstract: Age-related changes in maternal reproductive allocation for long-lived species are a key prediction from life-history theory.Theoretical and empirical work suggests that allocation may increase with age due to constraint (increases with experience) or restraint (increases with age in the face of declining residual reproductive value), and may decrease among the oldest aged animals due to senescence in reproductive function.Here, we use a hierarchical modelling approach to investigate the age-related patterns of change in maternal reproductive effort in the Weddell seal, a long-lived marine mammal with a protracted period of maternal care during which mothers allocate a large proportion of body mass while feeding little.We find that maternal allocation increases with age for young mothers during both the pre-natal and post-natal periods. In contrast, older mothers demonstrate a senescent decline in pre-natal allocation but allocate more of their declining resources to their offspring during the post-natal period. We also find strong evidence for the importance of individual effects in reproductive allocation among mothers: some mothers consistently produce heavier (or lighter) pups than expected.Our results indicate that maternal allocation changes over a mother's reproductive life span and that age-specific differences differ in notable ways in pre-natal and post-natal periods.The authors demonstrate that the pattern of reproductive energy allocation with age and maternal characteristics is markedly different in the pre-natal and post-natal phases of maternal care in a long-lived mammal. This has implications for the study of age-related patterns of reproductive effort insofar as the pattern depends on the trait measured.
PubDate: 2016-09-07T03:35:28.739958-05:
- Authors: John T. Paterson; Jay J. Rotella, Jennifer M. Mannas, Robert A. Garrott
- Carry-over effects on the annual cycle of a migratory seabird: an
experimental study
- Authors: Annette L. Fayet; Robin Freeman, Akiko Shoji, Holly L. Kirk, Oliver Padget, Chris M. Perrins, Tim Guilford
Abstract: Long-lived migratory animals must balance the cost of current reproduction with their own condition ahead of a challenging migration and future reproduction. In these species, carry-over effects, which occur when events in one season affect the outcome of the subsequent season, may be particularly exacerbated. However, how carry-over effects influence future breeding outcomes and whether (and how) they also affect behaviour during migration and wintering is unclear.Here we investigate carry-over effects induced by a controlled, bidirectional manipulation of the duration of reproductive effort on the migratory, wintering and subsequent breeding behaviour of a long-lived migratory seabird, the Manx shearwater Puffinus puffinus. By cross-fostering chicks of different age between nests, we successfully prolonged or shortened by ∼25% the chick-rearing period of 42 breeding pairs. We tracked the adults with geolocators over the subsequent year and combined migration route data with at-sea activity budgets obtained from high-resolution saltwater-immersion data. Migratory behaviour was also recorded during non-experimental years (the year before and/or two years after manipulation) for a subset of birds, allowing comparison between experimental and non-experimental years within treatment groups.All birds cared for chicks until normal fledging age, resulting in birds with a longer breeding period delaying their departure on migration; however, birds that finished breeding earlier did not start migrating earlier. Increased reproductive effort resulted in less time spent at the wintering grounds, a reduction in time spent resting daily and a delayed start of breeding with lighter eggs and chicks and lower breeding success the following breeding season. Conversely, reduced reproductive effort resulted in more time resting and less time foraging during the winter, but a similar breeding phenology and success compared with control birds the following year, suggesting that 'positive' carry-over effects may also occur but perhaps have a less long-lasting impact than those incurred from increased reproductive effort.Our results shed light on how carry-over effects can develop and modify an adult animal's behaviour year-round and reveal how a complex interaction between current and future reproductive fitness, individual condition and external constraints can influence life-history decisions.Increasing or decreasing reproductive effort in migratory birds in a controlled experiment results in oppositely directed carry-over effects, affecting migratory and wintering behaviour, and future breeding performance. This study helps understand how carry-over effects develop and affect the annual cycle of long-lived migratory animals, a central question in life-history theory.
PubDate: 2016-08-31T00:00:04.521162-05:
- Authors: Annette L. Fayet; Robin Freeman, Akiko Shoji, Holly L. Kirk, Oliver Padget, Chris M. Perrins, Tim Guilford
- The ontogeny of tolerance curves: habitat quality vs. acclimation in a
stressful environment
- Authors: Odrade Nougué; Nils Svendsen, Roula Jabbour-Zahab, Thomas Lenormand, Luis-Miguel Chevin
Abstract: Stressful environments affect life-history components of fitness through (i) instantaneous detrimental effects, (ii) historical (carry-over) effects and (iii) history-by-environment interactions, including acclimation effects. The relative contributions of these different responses to environmental stress are likely to change along life, but such ontogenic perspective is often overlooked in studies of tolerance curves, precluding a better understanding of the causes of costs of acclimation, and more generally of fitness in temporally fine-grained environments.We performed an experiment in the brine shrimp Artemia to disentangle these different contributions to environmental tolerance, and investigate how they unfold along life. We placed individuals from three clones of A. parthenogenetica over a range of salinities during a week, before transferring them to a (possibly) different salinity for the rest of their lives. We monitored individual survival at repeated intervals throughout life, instead of measuring survival or performance at a given point in time, as commonly done in acclimation experiments. We then designed a modified survival analysis model to estimate phase-specific hazard rates, accounting for the fact that individuals may share the same treatment for only part of their lives.Our approach allowed us to distinguish effects of salinity on (i) instantaneous mortality in each phase (habitat quality effects), (ii) mortality later in life (history effects) and (iii) their interaction. We showed clear effects of early salinity on late survival and interactions between effects of past and current environments on survival. Importantly, analysis of the ontogenetic dynamics of the tolerance curve reveals that acclimation affects different parts of the curve at different ages.Adopting a dynamical view of the ontogeny of tolerance curve should prove useful for understanding niche limits in temporally changing environments, where the full sequence of environments experienced by an individual determines its overall environmental tolerance, and how it changes throughout life.Environmental tolerance curves are broadly used to characterize fundamental niches, but ontogenic aspects of these curves are generally overlooked. Using an acclimation experiment and a modified survival analysis, the authors analyze how tolerance curves unfold along life, and show that treatments affect different parts of these curves at different ages.
PubDate: 2016-08-30T08:35:35.620042-05:
- Authors: Odrade Nougué; Nils Svendsen, Roula Jabbour-Zahab, Thomas Lenormand, Luis-Miguel Chevin
- Hunting promotes sexual conflict in brown bears
- Authors: Jacinthe Gosselin; Martin Leclerc, Andreas Zedrosser, Sam M. J. G. Steyaert, Jon E. Swenson, Fanie Pelletier
Abstract: The removal of individuals through hunting can destabilize social structure, potentially affecting population dynamics. Although previous studies have shown that hunting can indirectly reduce juvenile survival through increased sexually selected infanticide (SSI), very little is known about the spatiotemporal effects of male hunting on juvenile survival.Using detailed individual monitoring of a hunted population of brown bears (Ursus arctos) in Sweden (1991–2011), we assessed the spatiotemporal effect of male removal on cub survival.We modelled cub survival before, during and after the mating season. We used three proxies to evaluate spatial and temporal variation in male turnover; distance and timing of the closest male killed and number of males that died around a female's home range centre.Male removal decreased cub survival only during the mating season, as expected in seasonal breeders with SSI. Cub survival increased with distance to the closest male killed within the previous 1·5 years, and it was lower when the closest male killed was removed 1·5 instead of 0·5 year earlier. We did not detect an effect of the number of males killed.Our results support the hypothesis that social restructuring due to hunting can reduce recruitment and suggest that the distribution of the male deaths might be more important than the overall number of males that die. As the removal of individuals through hunting is typically not homogenously distributed across the landscape, spatial heterogeneity in hunting pressure may cause source–sink dynamics, with lower recruitment in areas of high human-induced mortality.The authors explored detailed spatiotemporal effects of male hunting on juvenile survival in brown bears, a species with sexually selected infanticide. The distribution of kills might be more important for juvenile survival than the number of males killed. Thus, reducing harvest intensity might not always increase population growth.
PubDate: 2016-08-30T08:35:33.021489-05:
- Authors: Jacinthe Gosselin; Martin Leclerc, Andreas Zedrosser, Sam M. J. G. Steyaert, Jon E. Swenson, Fanie Pelletier
- Direct and indirect genetic and fine-scale location effects on breeding
date in song sparrows
- Authors: Ryan R. Germain; Matthew E. Wolak, Peter Arcese, Sylvain Losdat, Jane M. Reid
Abstract: Quantifying direct and indirect genetic effects of interacting females and males on variation in jointly expressed life-history traits is central to predicting microevolutionary dynamics. However, accurately estimating sex-specific additive genetic variances in such traits remains difficult in wild populations, especially if related individuals inhabit similar fine-scale environments.Breeding date is a key life-history trait that responds to environmental phenology and mediates individual and population responses to environmental change. However, no studies have estimated female (direct) and male (indirect) additive genetic and inbreeding effects on breeding date, and estimated the cross-sex genetic correlation, while simultaneously accounting for fine-scale environmental effects of breeding locations, impeding prediction of microevolutionary dynamics.We fitted animal models to 38 years of song sparrow (Melospiza melodia) phenology and pedigree data to estimate sex-specific additive genetic variances in breeding date, and the cross-sex genetic correlation, thereby estimating the total additive genetic variance while simultaneously estimating sex-specific inbreeding depression. We further fitted three forms of spatial animal model to explicitly estimate variance in breeding date attributable to breeding location, overlap among breeding locations and spatial autocorrelation. We thereby quantified fine-scale location variances in breeding date and quantified the degree to which estimating such variances affected the estimated additive genetic variances.The non-spatial animal model estimated nonzero female and male additive genetic variances in breeding date (sex-specific heritabilities: 0·07 and 0·02, respectively) and a strong, positive cross-sex genetic correlation (0·99), creating substantial total additive genetic variance (0·18). Breeding date varied with female, but not male inbreeding coefficient, revealing direct, but not indirect, inbreeding depression. All three spatial animal models estimated small location variance in breeding date, but because relatedness and breeding location were virtually uncorrelated, modelling location variance did not alter the estimated additive genetic variances.Our results show that sex-specific additive genetic effects on breeding date can be strongly positively correlated, which would affect any predicted rates of microevolutionary change in response to sexually antagonistic or congruent selection. Further, we show that inbreeding effects on breeding date can also be sex specific and that genetic effects can exceed phenotypic variation stemming from fine-scale location-based variation within a wild population.The authors used 38 years of songbird data to estimate sex-specific additive genetic variances (VA) in breeding date while accounting for fine-scale location-based variance (VLoc). They found significant sex-specific VA, a strongly positive cross-sex genetic correlation and that modelling VLoc did not alter estimated VA when relatives breed in separate locations.
PubDate: 2016-08-30T08:35:25.892133-05:
- Authors: Ryan R. Germain; Matthew E. Wolak, Peter Arcese, Sylvain Losdat, Jane M. Reid
- Co-infections and environmental conditions drive the distributions of
blood parasites in wild birds
- Authors: Nicholas J. Clark; Konstans Wells, Dimitar Dimitrov, Sonya M. Clegg
Abstract: Experimental work increasingly suggests that non-random pathogen associations can affect the spread or severity of disease. Yet due to difficulties distinguishing and interpreting co-infections, evidence for the presence and directionality of pathogen co-occurrences in wildlife is rudimentary.We provide empirical evidence for pathogen co-occurrences by analysing infection matrices for avian malaria (Haemoproteus and Plasmodium spp.) and parasitic filarial nematodes (microfilariae) in wild birds (New Caledonian Zosterops spp.).Using visual and genus-specific molecular parasite screening, we identified high levels of co-infections that would have been missed using PCR alone. Avian malaria lineages were assigned to species level using morphological descriptions. We estimated parasite co-occurrence probabilities, while accounting for environmental predictors, in a hierarchical multivariate logistic regression.Co-infections occurred in 36% of infected birds. We identified both positively and negatively correlated parasite co-occurrence probabilities when accounting for host, habitat and island effects. Two of three pairwise avian malaria co-occurrences were strongly negative, despite each malaria parasite occurring across all islands and habitats. Birds with microfilariae had elevated heterophil to lymphocyte ratios and were all co-infected with avian malaria, consistent with evidence that host immune modulation by parasitic nematodes facilitates malaria co-infections. Importantly, co-occurrence patterns with microfilariae varied in direction among avian malaria species; two malaria parasites correlated positively but a third correlated negatively with microfilariae.We show that wildlife co-infections are frequent, possibly affecting infection rates through competition or facilitation. We argue that combining multiple diagnostic screening methods with multivariate logistic regression offers a platform to disentangle impacts of environmental factors and parasite co-occurrences on wildlife disease.Parasite competition and facilitation are expected to occur across many host systems, yet evidence from wildlife is limited and strongly biased towards mammal hosts. Using hierarchical multivariate modelling, the authors show that interspecific parasite interactions are common and may be important drivers of blood parasite distributions in wild avian hosts.
PubDate: 2016-08-26T03:15:30.170192-05:
- Authors: Nicholas J. Clark; Konstans Wells, Dimitar Dimitrov, Sonya M. Clegg
- Elevation and latitude interact to drive life-history variation in
precocial birds: a comparative analysis using galliformes
- Authors: Priya Balasubramaniam; John T. Rotenberry
Abstract: Elevational gradients provide a powerful laboratory for understanding the environmental and ecological drivers of geographic variation in avian life-history strategies. Environmental variation across elevational gradients is hypothesized to select for a trade-off of reduced fecundity (lower clutch size and/or fewer broods) for higher offspring quality (larger eggs and/or increased parental care) in higher elevation species and populations. In birds, a focus on altricial species from north temperate latitudes has prevented an evaluation of the generality of this trade-off, and how it is affected by latitude and intrinsic factors (development mode).We performed a comparative analysis controlling for body size and phylogenetic relationships on a global data set of 135 galliform species to test (i) whether higher elevation precocial species have lower fecundity (smaller clutch and/or fewer broods) and invest more in offspring quality (greater egg mass) and (ii) whether latitude influences the traits involved and/or the trade-off, and (iii) to identify ecological and environmental drivers of life-history variation along elevational gradients.Life-history traits showed significant interaction effects across elevation and latitude: temperate higher elevation species had smaller clutches and clutch mass, larger eggs and shorter incubation periods, whereas more tropical species had larger clutches, eggs and clutch mass, and longer incubation periods as elevation increased. Number of broods and body mass did not vary with elevation or latitude. Latitudinal gradient in clutch size was observed only for low-elevation species.Significantly, an overlooked latitude-by-elevation interaction confounds our traditional view of clutch size variation across a tropical-to-temperate gradient. Across all latitudes, higher elevation species invested in offspring quality via larger eggs but support for reduced fecundity resulting from smaller clutches was found only along temperate elevational gradients; contrary to expectations, tropical high-elevation species showed increased fecundity. Variation in nest predation risk could explain differences between temperate and tropical elevational gradients, but we lack a consistent mechanism to explain why predation risk should vary in this manner. Alternatively, a resource availability hypothesis based on physical attributes that globally differ between elevation and latitude (seasonality in day length and temperature) seems more plausible.For the first time, using precocial species the authors show that elevation and latitude interact to drive avian life-history variation and the well-known latitudinal gradient in clutch size is limited to low-elevation species. Results support the fecundity vs. offspring quality trade-off at higher elevations in temperate latitudes across different developmental modes.
PubDate: 2016-08-18T08:10:25.661844-05:
- Authors: Priya Balasubramaniam; John T. Rotenberry
- Mammalian engineers drive soil microbial communities and ecosystem
functions across a disturbance gradient
- Authors: David J. Eldridge; Manuel Delgado-Baquerizo, Jason N. Woodhouse, Brett A. Neilan
Abstract: The effects of mammalian ecosystem engineers on soil microbial communities and ecosystem functions in terrestrial ecosystems are poorly known. Disturbance from livestock has been widely reported to reduce soil function, but disturbance by animals that forage in the soil may partially offset these negative effects of livestock, directly and/or indirectly by shifting the composition and diversity of soil microbial communities. Understanding the role of disturbance from livestock and ecosystem engineers in driving soil microbes and functions is essential for formulating sustainable ecosystem management and conservation policies.We compared soil bacterial community composition and enzyme concentrations within four microsites: foraging pits of two vertebrates, the indigenous short-beaked echidna (Tachyglossus aculeatus) and the exotic European rabbit (Oryctolagus cuniculus), and surface and subsurface soils along a gradient in grazing-induced disturbance in an arid woodland.Microbial community composition varied little across the disturbance gradient, but there were substantial differences among the four microsites. Echidna pits supported a lower relative abundance of Acidobacteria and Cyanobacteria, but a higher relative abundance of Proteobacteria than rabbit pits and surface microsites. Moreover, these microsite differences varied with disturbance. Rabbit pits had a similar profile to the subsoil or the surface soils under moderate and high, but not low disturbance.Overall, echidna foraging pits had the greatest positive effect on function, assessed as mean enzyme concentrations, but rabbits had the least. The positive effects of echidna foraging on function were indirectly driven via microbial community composition. In particular, increasing activity was positively associated with increasing relative abundance of Proteobacteria, but decreasing Acidobacteria.Our study suggests that soil disturbance by animals may offset, to some degree, the oft-reported negative effects of grazing-induced disturbance on soil function. Further, our results suggest that most of this effect will be derived from echidnas, with little positive effects due to rabbits. Activities that enhance the habitat for echidnas or reduce rabbit populations are likely to have a positive effect on soil function in these systems.This study highlights the links between the activity of two mammals and ecosystem function in drylands. Animal disturbance alters microbial composition, markedly altering both soil enzymes and therefore ecosystem functioning. These data show that the effects on function are positive for the native echidna but negative for the exotic rabbit.
PubDate: 2016-08-18T05:45:31.241607-05:
- Authors: David J. Eldridge; Manuel Delgado-Baquerizo, Jason N. Woodhouse, Brett A. Neilan
- Multihost Bartonella parasites display covert host specificity even when
transmitted by generalist vectors
- Authors: Susan M. Withenshaw; Godefroy Devevey, Amy B. Pedersen, Andy Fenton
Abstract: Many parasites infect multiple sympatric host species, and there is a general assumption that parasite transmission between co-occurring host species is commonplace. Such between-species transmission could be key to parasite persistence within a disease reservoir and is consequently an emerging focus for disease control.However, while a growing body of theory indicates the potential importance of between-species transmission for parasite persistence, conclusive empirical evidence from natural communities is lacking, and the assumption that between-species transmission is inevitable may therefore be wrong.We investigated the occurrence of between-species transmission in a well-studied multihost parasite system. We identified the flea-borne Bartonella parasites infecting sympatric populations of Apodemus sylvaticus (wood mice) and Myodes glareolus (bank voles) in the UK and confirmed that several Bartonella species infect both rodent species. However, counter to previous knowledge, genetic characterization of these parasites revealed covert host specificity, where each host species is associated with a distinct assemblage of genetic variants, indicating that between-species transmission is rare.Limited between-species transmission could result from rare encounters between one host species and the parasites infecting another and/or host–parasite incompatibility. We investigated the occurrence of such encounter and compatibility barriers by identifying the flea species associated with each rodent host, and the Bartonella variants carried by individual fleas. We found that the majority of fleas were host-generalists but the assemblage of Bartonella variants in fleas tended to reflect the assemblage of Bartonella variants in the host species they were collected from, thus providing evidence of encounter barriers mediated by limited between-species flea transfer. However, we also found several fleas that were carrying variants never found in the host species from which they were collected, indicating some degree of host–pathogen incompatibility when barriers to encounter are overcome.Overall, these findings challenge our default perceptions of multihost parasite persistence, as they show that despite considerable overlaps in host species ecology, separate populations of the same parasite species may circulate and persist independently in different sympatric host species. This questions our fundamental understanding of endemic transmission dynamics and the control of infection within natural reservoir communities.Where sympatric species are infected by the same parasite, transmission between host species is often assumed. The authors challenge this, showing that transmission of flea-borne bacteria between sympatric species of wild rodents is rare, which likely results from a combination of limited between-species transfer of generalist vectors and host–parasite incompatibility.
PubDate: 2016-08-16T10:00:25.925233-05:
- Authors: Susan M. Withenshaw; Godefroy Devevey, Amy B. Pedersen, Andy Fenton
- Consistent scaling of population structure across landscapes despite
intraspecific variation in movement and connectivity
- Authors: Brian E. Reichert; Robert J. Fletcher, Christopher E. Cattau, Wiley M. Kitchens
Abstract: Understanding the spatial scale of population structure is fundamental to long-standing tenets of population biology, landscape ecology and conservation. Nonetheless, identifying such scales has been challenging because a key factor that influences scaling – movement among patches or local populations – is a multicausal process with substantial phenotypic and temporal variation.We resolve this problem via a novel application of network modularity. When applied to movements, modularity provides a formal description of the functional aggregation of populations and identifies potentially critical scales for ecological and evolutionary dynamics. We first test for modularity using several different types of biologically relevant movements across the entire geographic range of an endangered bird, the snail kite (Rostrhamus sociabilis plumbeus). We then ask whether variation in movement based on (i) age, (ii) sex and (iii) time (annual, seasonal and within-season movements) influences spatial population structure (i.e. modularity) in snail kites.We identified significant modularity in annual dispersal of snail kites (all adults, males only, females only, and juveniles only) and in within-breeding season movements of adults, yet no evidence of modularity in seasonal (non-breeding) movements. For those movements with observed modular structure, we found striking similarities in the spatial configuration of population structure, even though movement properties varied considerably among these different types of movements.Our results suggest that the emergence of modularity in population networks can be robust despite movement heterogeneity and differences in patch-based measures of connectivity. Furthermore, our comparison of the population structure and connectivity across multiple movement phases helps to identify wetland patches most critical to population connectivity at multiple spatiotemporal scales.We argue that understanding modularity in populations may provide a robust complement to existing measures of population structure and connectivity and will help to clarify the limiting roles of movement for populations. Such information is increasingly needed for interpreting population persistence and guiding effective conservation strategies with ongoing environmental change.Spatial scales of population structure are challenging to identify because of phenotypic and temporal variation in movements. Using network modularity, the authors test for variation in structure and connectivity among different types of movements of an endangered bird. The results suggest that population structure can be robust despite movement heterogeneity.
PubDate: 2016-08-15T03:50:27.417822-05:
- Authors: Brian E. Reichert; Robert J. Fletcher, Christopher E. Cattau, Wiley M. Kitchens
- High adult mortality in disease-challenged frog populations increases
vulnerability to drought
- Authors: Ben C. Scheele; David A. Hunter, Sam C. Banks, Jennifer C. Pierson, Lee F. Skerratt, Rebecca Webb, Don A. Driscoll
Abstract: Pathogen emergence can drive major changes in host population demography, with implications for population dynamics and sensitivity to environmental fluctuations. The amphibian disease chytridiomycosis, caused by infection with the fungal pathogen Batrachochytrium dendrobatidis (Bd), is implicated in the severe decline of over 200 amphibian species. In species that have declined but not become extinct, Bd persists and can cause substantial ongoing mortality. High rates of mortality associated with Bd may drive major changes in host demography, but this process is poorly understood.Here, we compared population age structure of Bd-infected populations, Bd-free populations and museum specimens collected prior to Bd emergence for the endangered Australian frog, Litoria verreauxii alpina (alpine tree frog). We then used population simulations to investigate how pathogen-associated demographic shifts affect the ability of populations to persist in stochastic environments.We found that Bd-infected populations have a severely truncated age structure associated with very high rates of annual adult mortality. Near-complete annual adult turnover in Bd-infected populations means that individuals breed once, compared with Bd-free populations where adults may breed across multiple years.Our simulations showed that truncated age structure erodes the capacity of populations to withstand periodic recruitment failure; a common challenge for species reproducing in uncertain environments.We document previously undescribed demographic shifts associated with a globally emerging pathogen and demonstrate how these shifts alter host ecology. Truncation of age structure associated with Bd effectively reduces host niche width and can help explain the contraction of L. v. alpina to perennial waterbodies where the risk of drought-induced recruitment failure is low. Reduced capacity to tolerate other sources of mortality may explain variation in decline severity among other chytridiomycosis-challenged species and highlights the potential to mitigate disease impacts through minimizing other sources of mortality.This paper provides new insights into how the disease chytridiomycosis impacts amphibian demography and ecology. The authors show that the disease is associated with the truncation of adult age structure. Loss of individuals capable of reproducing across multiple years effectively reduces niche breadth through reduced capacity to tolerate recruitment failure.
PubDate: 2016-08-15T03:35:31.189115-05:
- Authors: Ben C. Scheele; David A. Hunter, Sam C. Banks, Jennifer C. Pierson, Lee F. Skerratt, Rebecca Webb, Don A. Driscoll
- Genetic mixture of multiple source populations accelerates invasive range
- Authors: Natalie K. Wagner; Brad M. Ochocki, Kerri M. Crawford, Aldo Compagnoni, Tom E.X. Miller
Abstract: A wealth of population genetic studies have documented that many successful biological invasions stem from multiple introductions from genetically distinct source populations. Yet, mechanistic understanding of whether and how genetic mixture promotes invasiveness has lagged behind documentation that such mixture commonly occurs. We conducted a laboratory experiment to test the influence of genetic mixture on the velocity of invasive range expansion.The mechanistic basis for effects of genetic mixture could include evolutionary responses (mixed invasions may harbour greater genetic diversity and thus elevated evolutionary potential) and/or fitness advantages of between-population mating (heterosis). If driven by evolution, positive effects of source population mixture should increase through time, as selection sculpts genetic variation. If driven by heterosis, effects of mixture should peak following first reproductive contact and then dissipate.Using a laboratory model system (beetles spreading through artificial landscapes), we quantified the velocity of range expansion for invasions initiated with one, two, four or six genetic sources over six generations. Our experiment was designed to test predictions corresponding to the evolutionary and heterosis mechanisms, asking whether any effects of genetic mixture occurred in early or later generations of range expansion. We also quantified demography and dispersal for each experimental treatment, since any effects of mixture should be manifest in one or both of these traits.Over six generations, invasions with any amount of genetic mixture (two, four and six sources) spread farther than single-source invasions. Our data suggest that heterosis provided a 'catapult effect', leaving a lasting signature on range expansion even though the benefits of outcrossing were transient. Individual-level trait data indicated that genetic mixture had positive effects on local demography (reduced extinction risk and enhanced population growth) during the initial stages of invasion but no consistent effects on dispersal ability.Our work is the first to demonstrate that genetic mixture can alter the course of spatial expansion, the stage of invasion typically associated with the greatest ecological and economic impacts. We suggest that similar effects of genetic mixture may be a common feature of biological invasions in nature, but that these effects can easily go undetected.Genetic mixture of multiple source populations can catapult the spread of biological invasions.
PubDate: 2016-08-08T10:22:21.413438-05:
- Authors: Natalie K. Wagner; Brad M. Ochocki, Kerri M. Crawford, Aldo Compagnoni, Tom E.X. Miller
- The modulating role of group stability on fitness effects of group size is
different in females and males of a communally rearing rodent
- Authors: Luis A. Ebensperger; Loreto A. Correa, Cecilia León, Juan Ramírez-Estrada, Sebastian Abades, Álvaro Villegas, Loren D. Hayes
Abstract: Group size may influence fitness benefits and costs that emerge from cooperative and competitive interactions in social species. However, evidence from plural breeding mammals indicates that group size is insufficient to explain variation in direct fitness, implying other attributes of social groups were overlooked.We studied the natural population of a social rodent during 5 years to test the hypothesis that social stability – in terms of group composition – modulates the effects of increasing number of breeding females (a proxy of communal rearing) and males on the number of offspring weaned (sired) and on the number of offspring weaned (sired) surviving to breeding age (two proxies of direct fitness). We quantified the effects of social stability (measured as changes in female or male group members between mating and the onset of lactation) on these fitness measures.We used live trapping, telemetry and DNA markers to determine social and fitness measures.Social stability in degus was variable in terms of the number of changes in group composition across groups. Low stability was mostly due to mortality and emigration of group members.Results supported a modulating role of social stability on the relationship between group size and the number of offspring weaned (sired). Stability in female and male group composition were both modulators of fitness to females and males.The modulatory role of stability was sex specific, where high social stability was often fitness beneficial to the females. Instead, low social stability was fitness enhancing to the males.The study shows how benefits of group living are conditioned by social stability in male and female group composition.
PubDate: 2016-08-02T04:17:10.115507-05:
- Authors: Luis A. Ebensperger; Loreto A. Correa, Cecilia León, Juan Ramírez-Estrada, Sebastian Abades, Álvaro Villegas, Loren D. Hayes
- Energy storage and fecundity explain deviations from ecological
stoichiometry predictions under global warming and size-selective
- Authors: Chao Zhang; Mieke Jansen, Luc De Meester, Robby Stoks
Abstract: A key challenge for ecologists is to predict how single and joint effects of global warming and predation risk translate from the individual level up to ecosystem functions. Recently, stoichiometric theory linked these levels through changes in body stoichiometry, predicting that both higher temperatures and predation risk induce shifts in energy storage (increases in C-rich carbohydrates and reductions in N-rich proteins) and body stoichiometry (increases in C : N and C : P). This promising theory, however, is rarely tested and assumes that prey will divert energy away from reproduction under predation risk, while under size-selective predation, prey instead increase fecundity.We exposed the water flea Daphnia magna to 4 °C warming and fish predation risk to test whether C-rich carbohydrates increase and N-rich proteins decrease, and as a result, C : N and C : P increase under warming and predation risk.Unexpectedly, warming decreased body C : N, which was driven by reductions in C-rich fat and sugar contents while the protein content did not change. This reflected a trade-off where the accelerated intrinsic growth rate under warming occurred at the cost of a reduced energy storage. Warming reduced C : N less and only increased C : P and N : P in the fish-period Daphnia. These evolved stoichiometric responses to warming were largely driven by stronger warming-induced reductions in P than in C and N and could be explained by the better ability to deal with warming in the fish-period Daphnia.In contrast to theory predictions, body C : N decreased under predation risk due to a strong increase in the N-rich protein content that offsets the increase in C-rich fat content. The higher investment in fecundity (more N-rich eggs) under predation risk contributed to this stronger increase in protein content. Similarly, the lower body C : N of pre-fish Daphnia also matched their higher fecundity.Warming and predation risk independently shaped body stoichiometry, largely by changing levels of energy storage molecules. Our results highlight that two widespread patterns, the trade-off between rapid development and energy storage and the increased investment in reproduction under size-selective predation, cause predictable deviations from current ecological stoichiometry theory.This paper demonstrates that global warming and size-selective predation risk can independently shape Daphnia magna body stoichiometry, which are largely driven by changes in energy storage molecules. Also, the trade-offs between energy storage and rapid development and the increased investment in fecundity under size-selective predation could explain deviations from ecological stoichiometry predictions. Photo credit: Joachim Mergeay.
PubDate: 2016-05-12T07:45:48.523325-05:
- Authors: Chao Zhang; Mieke Jansen, Luc De Meester, Robby Stoks
- Beyond neutral and forbidden links: morphological matches and the assembly
of mutualistic hawkmoth–plant networks
- Authors: Federico D. Sazatornil; Marcela Moré, Santiago Benitez-Vieyra, Andrea A. Cocucci, Ian J. Kitching, Boris O. Schlumpberger, Paulo E. Oliveira, Marlies Sazima, Felipe W. Amorim
Abstract: A major challenge in evolutionary ecology is to understand how co-evolutionary processes shape patterns of interactions between species at community level. Pollination of flowers with long corolla tubes by long-tongued hawkmoths has been invoked as a showcase model of co-evolution. Recently, optimal foraging models have predicted that there might be a close association between mouthparts' length and the corolla depth of the visited flowers, thus favouring trait convergence and specialization at community level.Here, we assessed whether hawkmoths more frequently pollinate plants with floral tube lengths similar to their proboscis lengths (morphological match hypothesis) against abundance-based processes (neutral hypothesis) and ecological trait mismatches constraints (forbidden links hypothesis), and how these processes structure hawkmoth–plant mutualistic networks from five communities in four biogeographical regions of South America.We found convergence in morphological traits across the five communities and that the distribution of morphological differences between hawkmoths and plants is consistent with expectations under the morphological match hypothesis in three of the five communities. In the two remaining communities, which are ecotones between two distinct biogeographical areas, interactions are better predicted by the neutral hypothesis.Our findings are consistent with the idea that diffuse co-evolution drives the evolution of extremely long proboscises and flower tubes, and highlight the importance of morphological traits, beyond the forbidden links hypothesis, in structuring interactions between mutualistic partners, revealing that the role of niche-based processes can be much more complex than previously known.The authors assessed whether hawkmoths more frequently visit plants with floral tube lengths similar to their proboscis lengths beyond abundance-based processes and ecological trait mismatches constraints. The findings highlight the importance of morphological traits matching, revealing that the role of niche-based processes can be much more complex than previously known.
PubDate: 2016-04-04T00:06:20.063831-05:
- Authors: Federico D. Sazatornil; Marcela Moré, Santiago Benitez-Vieyra, Andrea A. Cocucci, Ian J. Kitching, Boris O. Schlumpberger, Paulo E. Oliveira, Marlies Sazima, Felipe W. Amorim
- Natural history matters: how biological constraints shape diversified
interactions in pollination networks
- Authors: Pedro Jordano
First page: 1423
Abstract: Species-specific traits constrain the ways organisms interact in nature. Some pairwise interactions among coexisting species simply do not occur; they are impossible to observe despite the fact that partners coexist in the same place. The author discusses these 'forbidden links' of species interaction networks. Photo: the sphingid moth Agrius cingulata visiting a Bauhinia mollis flower; Las Yungas, Argentina. Courtesy of Andrea Cocucci.Sazatornil, F.D., Moré, M., Benitez-Vieyra, S., Cocucci, A.A., Kitching, I.J., Schlumpberger, B.O., Oliveira, P.E., Sazima, M. & Amorim, F.W. (2016) Beyond neutral and forbidden links: morphological matches and the assembly of mutualistic hawkmoth-plant networks. Journal of Animal Ecology, 85, 1586–1594.Species-specific traits and life-history characteristics constrain the ways organisms interact in nature. For example, gape-limited predators are constrained in the sizes of prey they can handle and efficiently consume. When we consider the ubiquity of such constrains, it is evident how hard it can be to be a generalist partner in ecological interactions: a free-living animal or plant cannot simply interact with every available partner it encounters. Some pairwise interactions among coexisting species simply do not occur; they are impossible to observe despite the fact that partners coexist in the same place. Sazatornil et al. () explore the nature of such constraints in the mutualisms among hawkmoths and the plants they pollinate. In this iconic interaction, used by Darwin and Wallace to vividly illustrate the power of natural selection in shaping evolutionary change, both pollinators and plants are sharply constrained in their interaction modes and outcomes.Species-specific traits constrain the ways organisms interact in nature. Some pairwise interactions among coexisting species simply do not occur; they are impossible to observe despite the fact that partners coexist in the same place. The author discusses these 'forbidden links' of species interaction networks. Photo: the sphingid moth Agrius cingulata visiting a Bauhinia mollis flower; Las Yungas, Argentina. Courtesy of Andrea Cocucci.
PubDate: 2016-10-19T03:37:21.316303-05:
- Authors: Pedro Jordano
- Merging elemental and macronutrient approaches for a comprehensive study
of energy and nutrient flows
- Authors: Shawn M. Wilder; Punidan D. Jeyasingh
First page: 1427
Abstract: Global warming and predation risk can have important impacts on animal physiology and life histories that can have consequences for ecosystem function. Zhang et al. () recently tested the separate and interactive effects of warming and predation risk on the body composition of Daphnia magna. By measuring both the elemental and biochemical composition of individuals, they showed that D. magna body elemental composition responded opposite to theoretical predictions and previous studies but that these changes were explained by adaptive life-history shifts in allocation to protein in eggs versus body lipid reserves. Photograph by Joachim Mergeay.Zhang, C., Jansen, M., De Meester, L. & Stoks, R. (2016) Energy storage and fecundity explain deviations from ecological stoichiometry predictions under global warming and size-selective predation. Journal of Animal Ecology 85, 1431–1441.Understanding the mechanisms through which energy and nutrients flow through ecosystems is critical to predicting and mitigating the consequences of climate change and other ecological disturbances. Ecological stoichiometry and nutritional geometry, using data on elements and macromolecules, respectively, have independently made major contributions towards this goal. Zhang et al. () provide data demonstrating that these two major frameworks can provide complementary insight into the consequences of global warming and predation risk for the physiology and life-history traits of a key aquatic herbivore, Daphnia magna. This study should catalyse further work to unite these two parallel and complementary frameworks.Global warming and predation risk can have important impacts on animal physiology and life histories that can have consequences for ecosystem function. Zhang et al. () recently tested the separate and interactive effects of warming and predation risk on the body composition of Daphnia magna. By measuring both the elemental and biochemical composition of individuals, they showed that D. magna body elemental composition responded opposite to theoretical predictions and previous studies but that these changes were explained by adaptive life-history shifts in allocation to protein in eggs versus body lipid reserves. Photograph by Joachim Mergeay.
PubDate: 2016-10-19T03:37:28.089274-05:
- Authors: Shawn M. Wilder; Punidan D. Jeyasingh