Topic 2.3- Island Biogeography

Island Biogeography

Definition

• Island biogeography is the study of ecological relationships and community structure on islands.
• Islands can be:
  • Actual islands: Land in the middle of water.
  • Figurative islands: Natural habitat surrounded by an urban environment or a developed human environment (e.g., Central Park in New York City).

Two Main Observations/Ideas

1. Larger Islands Support More Total Species (Higher Species Richness)

• Reason:
  • More ecosystem diversity.
  • More food and habitat sources.
  • More niches or ecological roles available.

2. Distance to the Mainland

• The closer an island is to the mainland, the higher the species richness.
• Easier for colonizers to reach the island.
  • Colonizers: Organisms that move from the mainland and establish a new population on the island.
• Easier for new organisms to migrate, increasing genetic diversity.
• Increased genetic diversity increases species resilience.

Island Size and Species Richness

Ecosystem Diversity

• Larger islands have higher ecosystem diversity, creating microhabitats with different food and habitat resources.

Population Size

• Larger space allows for larger population sizes, which leads to more genetic diversity and resistance to disturbance.
• Lower rate of extinction on larger islands.

Positive Correlation

• There is a positive correlation between island size and species richness.
• As island size increases, the number of species found there also increases.
• x = island size (square kilometers)
• y = number of species (species richness)
  • As x increases, y increases.

Distance to Mainland and Species Richness

Colonization

• The closer an island is to the mainland, the easier it is for species to colonize.
• Colonization: A population moving from the mainland to a new island ecosystem or habitat.
• Species often have to swim or fly to the island.

Genetic Diversity

• Closer islands experience more continual migration, leading to increased genetic diversity and larger population sizes.

Inverse Relationship

• There is an inverse relationship between distance from the mainland and species richness.
• As the distance from the island to the mainland increases, species richness decreases.
  • As distance increases, species decreases.

Evolution on Islands

Limited Resources

• Islands have limited space and resources, creating unique conditions for evolution.
• Increased pressure for species to adapt to narrower or more specific conditions.

Adaptive Radiation

• Adaptive radiation: A single species rapidly evolving into several new species to use different resources.
• Example: Galapagos finches
  • Different beak sizes evolved to utilize different food resources (cactus flowers, seeds, insects, plant buds).
  • Reduces competition.
• A common ancestor from the mainland evolved into multiple unique species with different beak sizes due to different food resources available in different microhabitats.

FRQ Practice

• Describe the process of organisms colonizing an island habitat.
• Describe how the island's distance from the mainland influences the number of species that will ultimately colonize that island.