1. Clutch sizes generally increase with latitude, and are smaller at southern latitudes compared with equivalent northern ones. 2. Descriptions of such patterns and attempts to identify their causal mechanisms are complicated as different species, with different ecological traits are often compared in different regions. We reduce such problems by using the introduction of 11 passerine species from the UK to New Zealand as a natural experiment to explore interspecific geographical variation in clutch size. 3. Nine species have significantly smaller clutches in New Zealand than the UK. Seasonality, measured both by climate and how birds respond to variation in resource availability, is also lower in New Zealand. Comparing across species, the magnitude of clutch size change is unrelated to the magnitude of reduced seasonality that each species experiences. 4. Such observations are partly compatible with Ashmole's hypothesis that areas with high seasonality have large clutch sizes (higher winter mortality results in a breeding population that is significantly lower than the environment's carrying capacity, and hence in extra resources for rearing chicks). However, additional data on seasonal changes in resource availability and population densities, combined with comparative data on survival and nest predation rates, are required to evaluate fully the mechanisms generating smaller clutches in the southern hemisphere. We discuss the potential determinants of geographical variation in the patterns of temporal variation in clutch size.
- latitudinal gradients
- introduced birds
- clutch size-lay date relationships
- Ashmole's hypothesis
1. Uwe na mtazamo wa kweli Ukubwa wa clutch kwa ujumla huongezeka na latitudo, na ni ndogo katika latitudo za kusini ikilinganishwa na zile sawa za kaskazini. 2. Uwezekano wa kupata Maelezo ya mifumo kama hiyo na majaribio ya kutambua utaratibu wao wa kisababishi ni ngumu kama spishi tofauti, na sifa tofauti za ikolojia mara nyingi kulinganishwa katika mikoa tofauti. Kwa mfano, katika utafiti wa utafiti wa 11 wa aina ya passerine kutoka Uingereza hadi New Zealand, tuligundua tofauti za kijiografia kati ya aina mbalimbali za ndege. 3. Uwe na mtazamo wa kweli Spishi tisa zina vifungo vidogo sana huko New Zealand kuliko Uingereza. Msimu, kupimwa kwa hali ya hewa na jinsi ndege kujibu tofauti katika upatikanaji wa rasilimali, pia ni chini katika New Zealand. Kwa kulinganisha kati ya spishi, ukubwa wa mabadiliko ya ukubwa wa clutch hauhusiani na ukubwa wa kupunguzwa kwa msimu ambao kila spishi hupata. 4. Uwe na uhakika Uchunguzi huo unalingana na nadharia ya Ashmole kwamba maeneo yenye msimu mkubwa yana ukubwa mkubwa wa clutch (kiwango cha juu cha vifo vya majira ya baridi huongoza kwa idadi ya uzazi ambayo ni chini sana kuliko uwezo wa kubeba mazingira, na kwa hivyo katika rasilimali za ziada kwa ajili ya kuzaa vifaranga). Hata hivyo, data za ziada juu ya mabadiliko ya msimu katika upatikanaji wa rasilimali na wiani wa idadi ya watu, pamoja na data za kulinganisha juu ya viwango vya kuishi na kuwinda kiota, zinahitajika ili kutathmini kikamilifu taratibu zinazozalisha clutches ndogo katika hemisphere ya kusini. Sisi kujadili sababu uwezekano wa tofauti kijiografia katika mifumo ya mabadiliko ya muda katika ukubwa clutch. - latitudinal gradients - introduced ndege - clutch ukubwa-lay tarehe mahusiano - Ashmole ya nadharia