Metapopulations - Introduction to Conservation Biology - Lecture Slides, Slides of Biology

Download Metapopulations - Introduction to Conservation Biology - Lecture Slides and more Slides Biology in PDF only on Docsity! Metapopulations • Objectives – Determine how e and c parameters influence metapopulation dynamics – Determine how the number of patches in a system affects the probability of local extinction and probability of regional extinction – Compare ‘propagule rain’ vs. ‘internal colonization’ metatpopulation dynamics – Evaluate how the ‘rescue effect’ affects metapopulation dynamics Docsity.com Metapopulations • There are relatively few examples where the entire population resides within a single patch • Most species are patchily distributed across space • Hence it becomes a population of populations…metapopulations Docsity.com Metapopulations • For a given patch, the likelihood of persistence for n years is simply • pn = (1 – pe)n • E.g. if a patch has a probability of persistence = 0.8 in a given year, the probability for 3 years = 0.83 = 0.512 • If we had 100 patches, approximately 52 would persist and 48 would go extinct Docsity.com Metapopulations • To consider the fate of the entire metapopulation (i.e. the probability of extinction of the entire population) • If all patches have the same probability of extinction, it is simply pex • For example, if pe=0.5 across 6 patches then Px = 1-(pe)x or 0.56 = 0.0156 or 1.5% Docsity.com Metapopulations • Now that we have defined e and c, let us consider the basic metapopulation model • where f is the fraction of patches occupied in the system (e.g. 5/25 = 0.2) • If f is the fraction of patches occupied, then 1- f is the fraction empty, the we can compute I as I = pi ( 1 - f ) df / dt = I -E Docsity.com Metapopulations • At equilibrium the fraction of patches is constant, although the exact combination is dynamic • The equilibrium fraction can be derived by setting the ‘rate’ to 0 dt/dt = 0 = pi – pif –pef and then f = pi / (pi + pe) Docsity.com Metapopulations • There are many important assumptions (as with any model), the most important being all patches are created equal; pe and pi are constant over time and apply to patches irrespective of population size and finally, spatial arrange and proximity are not important to pe or pi • You probably can imagine how when f is high, pi is probably large Docsity.com Metapopulations • This type of model is called the internal colonization model because colonization rates depend on current status (f) of the metapopulation system • Extinction of a patch may depend on the fraction of patches occupied in the system • When f is high, there are many potential colonists and pe decreases • This is termed the rescue effect Docsity.com