Ch. 23 - Geographic Ecology

Geographic Ecology

study of ecological structure & processes at large geographic scales

Frank Preston & Nilsson et al. island area and species richness

On islands species richness increases with increasing area

Island isolation and species richness

On islands, species richness decreases with isolation

• less isolated islands have higher migration potential

Large scale trends on islands

“island” size/area positively correlated with spp. richness

“island” isolation negatively correlated with spp. richness

Equilibrium Model of Island Biogeography

Number of species on islands is the result of a dynamic balance between rates of immigration and extinction

Immigration rates

Highest on new islands with no organisms

• rates decline as spp. richness increases

Extinction rates

increases with increasing numbers of spp.

• presence of more spp. = larger pool of potential extinctions

Where lines cross ——>

predicts # of spp. that will occur on island

Immigration tied to distance from source:

isolation

Extinction tied to island size

Area

Species richness generally increases towards:

equator

Time Since Perturbation Hypothesis

More spp. in tropics because tropics are older and disturbed less frequently.

• more time for speciation

• less frequent disturbance (reduces extinction rates)

• Intermediate hypothesis doesn’t apply here because: …

Productivity Hypothesis

High productivity in tropical environments contributes to high species richness.

• sometimes increased productivity can reduce spp. richness

Favorableness Hypothesis

Tropics provide more favorable environments than higher latitudes.

Area Hypothesis

Tropics cover greater area than higher latitudes leading to greater species richness

• more land & more uniform temps.

• larger spp. ranges increase allopatric speciation rates

Remote Sensing

Gathering info about an object w/o direct contact with it.

Geographic Information Systems (GIS)

Computer-based systems for storing, sorting, analyzing, & displaying geographic data.