Overview
This lecture covers the theory of island biogeography, focusing on how island size and distance from the mainland affect species richness, and explains the evolutionary impacts using examples like the Galapagos finches.
What is Island Biogeography?
- Island biogeography studies ecological relationships and community structure on islands, including both physical and habitat "islands" (isolated natural habitats).
- Habitat islands can be natural areas surrounded by human development, not just land surrounded by water.
Factors Affecting Species Richness
- Larger islands support more total species due to higher ecosystem and habitat diversity.
- Greater ecosystem diversity creates more food sources and ecological niches, supporting a wider variety of species.
- Larger islands allow for larger population sizes, increasing genetic diversity and resilience to disturbances.
- Closer islands to the mainland have higher species richness because it is easier for organisms (colonizers) to migrate and establish populations.
- Increased migration from the mainland brings greater genetic diversity, supporting species establishment and survival.
Relationships in Island Biogeography
- There is a positive correlation between island size and species richness; as island size increases, the number of species increases.
- There is an inverse relationship between distance from the mainland and species richness; as distance increases, species richness decreases.
- The ability of species to reach distant islands decreases with distance, reducing overall species diversity on far islands.
Evolutionary Impacts on Islands
- Limited space and resources on islands increase pressure for species to adapt to specific niches.
- Adaptive radiation is the process where a single species rapidly evolves into several new species to exploit different available resources and reduce competition.
- Example: Galapagos finches developed different beak shapes to utilize diverse food sources across microhabitats, leading to multiple distinct species from a common ancestor.
Key Terms & Definitions
- Island Biogeography — Study of the distribution and diversity of species on islands and isolated habitats.
- Species Richness — The number of different species present in an area.
- Colonizers — Organisms that migrate from the mainland to establish new populations on islands.
- Adaptive Radiation — Rapid evolution of multiple new species from a common ancestor to fill various ecological niches.
- Positive Correlation — Relationship where both variables increase together.
- Inverse Relationship — Relationship where one variable increases as the other decreases.
Action Items / Next Steps
- Practice describing the process of organisms colonizing an island and how island distance from the mainland affects species diversity.