Lecture 22: Dispersal, Metapopulations, and Island Biogeography Flashcards
How is sweet, fleshy fruit an adaptation?
It attracts animal pollinators which can disperse the seeds in their stool (heavier seeds can be dispersed this way when they cannot be dispersed by wind or water)
Dispersal allows organisms to
- colonize new areas
- escape competition
- avoid inbreeding depression
metapopulation and metacommunity
- collections of spatially distinct populations connected via dispersal
- set of local communities linked by the dispersal of one or more of their constituent species
patch
each spatially distinct population within a metapopulation
source-sink dynamics
one patch is a source the other is a sink (locally extinct without being globally extinct)
Areas which can often be locally unstable but globally stable
archipelagos (each island can have different population dynamics) so long as there is occasional dispersal between islands
What is tracked with patch dynamics
patch occupancy through time (instead of individuals)
Colonization of patches is affected by…
Fraction of currently occupied patches (P)
- higher P means more colonizers
- but also higher P means fraction of empty patches available to colonize is less
Metapopulation structure facilitates
species persistence and coexistence
If species A always outcompetes species B within a habitat patch…
local coexistence is impossible, but global coexistence could be possible
Global coexistence of species A and B requires (when A always outcompetes B in a patch)
- that A must go extinct in a patch OR new patches must be created from time to time
- B must be a better disperser than A
- B must be a fugitive/tramp/weedy/opportunistic/transient species
When local coexistence is impossible but global coexistence is, this is known as a…
competition-colonization tradeoff
populations can be driven to extinction by…
- stochastic forces: chance fluctuations in population numbers
- competitive exclusion
- predator prey interactions
- Allee effects at low density
Without migration…
patches that went extinct would stay extinct
What determines the number of species on an island?
- colonization: species can arrive from elsewhere
- extinction: species can go locally extinct on an island
- in-situ speciation: a lineage can split in two on an island but it will be a very slow process