IBD, which include sample size, metabolism, and taxa. For example, based on the meta-analysis, ectotherms are more likely than endotherms to display greater IBD. Metapopulation theory Metapopulation theory dictates that a metapopulation consists of spatially distinct populations that interact with one another on some level and move through a cycle of extinctions and recolonizations (i.e. through dispersal). The most common metapopulation model is the extinction-recolonization model which explains systems in which spatially distinct populations undergo stochastic changes in population sizes which may lead to extinction at the population level. Once this has occurred, dispersing individuals from other populations will immigrate and "rescue" the population at that site. Other metapopulation models include the source-sink model (island-mainland model) where one (or multiple) large central population(s) produces disperses to smaller satellite populations that have a population growth rate of less than one and could not persist without the influx from the main population. Metapopulation structure and the repeated extinctions and recolonizations can significantly affect a population's genetic structure. Recolonization by a few dispersers leads to population bottlenecks which will reduce the effective population size (Ne), accelerate genetic drift, and deplete genetic variation. However, dispersal between populations in the metapopulation can reverse or halt these processes over the long term. Therefore, in order for individual sub-populations to remain healthy, they must either have a large population size or have a relatively high rate of dispersal with other subpopulations. Molecular ecology focuses on using tests to determine the rates of dispersal between populations and can use molecular clocks to determine when historic bottlenecks occurred. As habitat becomes more fragmented, dispersal between populations will become increasingly rare. Therefore, subpopulations that may have historically been preserved by a metapopulation structure may start to decline. Using mitochondrial or nuclear markers to monitor dispersal coupled with population Fst values and allelic richness can provide insight into how well a population is performing and how it will perform into the future. Molecular clock hypothesis The molecular clock hypothesis states that DNA sequences roughly evolve at the same rate and because of this the dissimilarity between two sequences can be used to tell how long ago they diverged from one another. The first step in using a molecular clock is it must be calibrated based on the approximate time the two lineages studied diverged. The sources usually used to calibrate the molecular clocks are fossils or known geological events in the