Biodiversity and Island Biogeography

Direct Effect

Immediate impact between two species

Ex. Gold eagle eating fox

Ex. Removal of Kangaroo Rats caused house mouse population to increase

Indirect Effect

Impact occurs through a third party

Ex. Pig subsidizing eagle so it can stay on the island, then picking off the fox

Ex. After 7 years of the experiment, one seed was not getting eaten by anybody and slowly took over the enclosures and shaded out the other plants and ants

Extinction

Occurs naturally, but there are three anthropogenic reasons for extinction:

1. Overexploitation (pigeons, American bison)

2. Invasive species and ecological homogenization (losing distinctiveness)

3. Habitat conversion and destruction – biggest reason

Overexploitation

Ex. Passenger pigeons used to be the most abundant species of bird but went extinct

• Lived on oak and acorns, the resource base was limited by agriculture

• Heavily hunted - Allee Effect

Ex. American Buffalo

• Killed as humans moved toward west and to suppress indigenous populations

Invasive Species and Ecological Homogenization

Reducing the distinctiveness between realms when introducing new species to an environment

Ex.

• E.O Wilson - discovered the fire ant

• Nile perch

• Burmese pythons

• Chytrid fungus

Habitat Conversion and Construction

Urban area, ranch lands, agriculture

Endemic

Species only occurs in one area

Is extinction a problem?

We don't have names for most organisms - so we don't know whether a species' population is increasing or decreasing

Umbrella Species

Charismatic Megafauna (Manatees, Giant Pandas, Red Pandas)

Species-Area Relationship

Greater area increases species richness - indicates species number reaches an equilibrium

• Larger/Closer islands = higher rates of immigration and lower rates of extinction

• Small/Isolated Islands = Lowest rates of immigration and highest rates of extinction

Equilibrium Model of Island Biogeography

• Explained why big islands had more species

• Number of species increases (curve of immigration) → at some point, all the species that can get there, get there (pool of species) → All the niches are filled (extinction/extirpation curve) → number of species on the island is at an equilibrium

Island Biogegraphy Model

• Species-area relationship: How big the island is, how far the island is from the colonization source

• Species isolation-relationship

• Species turnover

1. Diversity is driven by two factors

   1. Distance from mainland

   2. Island size

2. Assumptions

   1. Evolutionary history is not important

   2. Characteristics of island habitats is not important

Species Richness

• Larger/Closer islands = higher rates of immigration and lower rates of extinction

• Small/Isolated Island = Lowest rates of immigration and highest rates of extinction

• Rate/Probability of Colonization = Rate/Probability of Extinction - Make sure you know how to draw this!

Genetic Drift

Allele fixation occurs more slowly in large populations; more new mutations in the total population

Extinction Debt

Delayed extinction of species or populations due to past environmental changes, like habitat loss or degradation, that have already had a significant impact on the ecosystem

Extinction Rate

Extinction rates for all these groups are increasing rapidly - 7000x higher than the last extinction

Anthropogenic causes of extinction

If we cause habitat loss, we won’t immediately see lots of extinction 

- Lag of time between habitat loss and extinction 

- More evident for short lived organisms bc long lived same 

  generations will be there for longer time