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BIOB50 LECTURE 21.docx

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Biological Sciences
Marc Cadotte

BIOB50 LECTURE 19: Metapopulations and Metacommunities Metapopulations  Isolated populations do affect one another’s pop dynamics because individuals/gametes occasionally disperse from one pop to another  such a group of interacting populations= metapopulation=population of populations  Many species have a metapopulation structure in which sets of spatially isolated pops are linked by dispersal for many species areas of suitable habitat exist as a series of favorable sites that are spatially isolated from one another  Meta= Greek for about itself in science it it translated as something of something i.e. meta- analyses= analysis of analyses  Hufaker: can see through time where and when prey/predators are over time and how they occupy different locations at different times  Metapopulations: spatially isolated pops that are linked by the dispersal of individuals or gametes  Metapopulations are characterized by repeated extinctions and colonizations  Patches are prone to extinction for two reasons o 1) if small, they have small pop sizes= more likely to go extinct= demographic stochasticity o 2) environmental conditions often change in a rapid and unpredictable manner = environmental stochasticity  Metapopulations aid persistence of populations although the individual pops may be prone to extinction, the collection of pops, the metapopulation persists since it includes pops that are going extinct and new pops established by colonization  Proportion (p) of patches occupied can be predicted in terms of extinction and colonization of habitat patches o dp/dt= immigration rate-extinction rate o extinction and colonization of habitat patches can be described by this equation dp/dt=cp(1-p)-ep o p=proportion of habitat patches that are occupied at time t o c=patch colonization rate o e=patch extinction rate o for a metapopulation to persist for a long time, the ratio e/c must be less than 1 o this equation has several assumptions  1)there is an infinite number of identical habitat patches=unrealistic  2) all patches have an equal chance of receiving colonists (i.e. distance)=unrealistic  3) All patches have an equal chance of extinction (i.e. size)  4) once a patch is colonized, its pop increases to its carrying capacity more rapidly than the rates of colonization and extinction (allows pop dynamics within patches to be ignored) o Levins: dp/dt=cp(1-p)-ep cp(1-p)= immigration=qudratically related (parabola with maximum seen on graph) and ep=extinction =linearly related (straight diagonal line) o From the intersection of the two plots of extinction and immigration, we can find the equilibrium point  Proportion of patches occupied= 1-e/c (at equilibrium) p=1-e/c  Metapopulations have led to research on key issues o How to estimate factors that influence patch colonization and extinction o Importance of the spatial arrangement of suitable patches o Extent to which the landscape between habitat patches affect dispersal o How to determine whether empty patches are suitable habitat or not o It also helps to study how fragmentation of habitat affects patch occupation (p) parches may become ever smaller and more isolated, reducing colonization rate and increasing extinction rate e/c ratio increases via habitat fragmentation o Metapopulation can go extinct even when suitable habitat remains i.e. the northern spotted owl the population decreased due to logging since they cant use the trees for habitat  in stuldies of the northern spotted owl in old growth forests in the Pacific NW, it was estimated that the entire metapopulation would collapse is logging were to reduce the fraction of suitable patches to l
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