Lecture 22: Community ecology: dispersal, metapopulations, and island biogeography

Macarthur and Wilson

Developed the theory of island biogeography, which predicts the number of species on an island based on size and isolation.

Dispersal

Movement of individuals between populations, aiding in colonization, competition escape, and avoiding inbreeding.

Metapopulations

Groups of spatially distinct populations connected by dispersal.

• Composed of patches that can go extinct but are recolonized by individuals from other patches.

Metapopulations: Sources

High-quality habitat patches that produce more dispersers.

Metapopulations: Sinks

Lower-quality habitat patches that would go extinct without migrants from sources.

Species Coexistence in Metapopulations

• Metapopulations allow for persistence even when some local populations are doomed.

• Coexistence can occur if species go extinct in certain patches or if new patches are created.

Competition-colonization trade-off

Species that are better at dispersing (e.g., "fugitive" species) can coexist with dominant competitors that outcompete them locally.

Levin’s Patch Occupancy Model

Describes how colonization and extinction rates influence the occupancy of patches over time.

• Equilibrium occurs when colonization = extinction

Levin’s patch occupancy model - key equation

dp/dt=cP(1−P)−eP

c is the colonization rate

e is the extinction rate.

Pika example

Research in Bodie, California showed how pikas utilize patch dynamics for population persistence, with some patches being stable and others undergoing cycles of extinction and recolonization.

Metacommunities

A network of local communities connected by the dispersal of species.

• Broader than metapopulations, involving interactions within and between communities