Overview

Island Biogeography is a scientific field that explores the ecological relationships and distribution of species on islands and isolated habitats. It examines how factors like island size, distance from the mainland, immigration, extinction, and habitat diversity influence biodiversity. The theory, foundational to modern ecology, offers insights into conservation, species richness, and the impacts of human activity.

Historical Context

The formalization of Island Biogeography began with Robert MacArthur and E.O. Wilson’s seminal work, The Theory of Island Biogeography (1967). Their research synthesized observations from tropical islands, proposing mathematical models to predict species richness based on island area and isolation. Earlier naturalists, including Charles Darwin and Alfred Russel Wallace, noted unique island fauna and flora, laying the groundwork for biogeographical studies.

  • Darwin (1835): Galápagos finches and adaptive radiation.
  • Wallace (1859): Malay Archipelago and species distribution boundaries (“Wallace Line”).

The theory revolutionized conservation biology, especially in understanding habitat fragmentation and reserve design.

Core Principles

1. Species-Area Relationship

Larger islands support more species due to increased habitat diversity and resources.

2. Distance Effect

Islands closer to the mainland have higher immigration rates, resulting in greater species richness.

3. Dynamic Equilibrium

Species richness on islands is a balance between immigration and extinction rates.

4. Turnover Rate

Species composition changes over time, even if the total number of species remains stable.

Key Models and Diagrams

Island Biogeography Model MacArthur-Wilson Equilibrium Model: Immigration and extinction rates intersect to determine equilibrium species number.

Factors Influencing Island Biodiversity

  • Island Size: Larger islands = lower extinction rates.
  • Isolation: More isolated = lower immigration rates.
  • Habitat Diversity: Varied environments support more niches.
  • Human Impact: Habitat destruction, invasive species, pollution.

Case Study: Plastic Pollution in Remote Oceanic Islands

Henderson Island (South Pacific)

Henderson Island, a UNESCO World Heritage site, is one of the world’s most remote islands. Despite its isolation, it has been found to have the highest density of plastic debris recorded anywhere on Earth. Researchers estimate over 37.7 million pieces of plastic, weighing 17.6 tons, have accumulated on its beaches (Lavers et al., 2020). This pollution affects native species, disrupts nesting habitats, and introduces toxins into food webs.

Diagram

Plastic Pollution on Henderson Island Plastic debris on Henderson Island beach.

Implications

  • Species Extinction: Ingestion and entanglement threaten endemic species.
  • Altered Ecosystem Dynamics: Pollution changes nutrient cycles, affects food webs.
  • Human Footprint: Demonstrates global reach of anthropogenic impacts.

Surprising Facts

  1. Plastic Debris in the Deepest Trenches: Microplastics have been discovered in the Mariana Trench, the deepest part of the ocean, demonstrating that even the most inaccessible habitats are not immune to human pollution (Peng et al., 2020).
  2. Rapid Species Turnover: Some islands can lose and gain up to 20% of their species within a decade, highlighting the instability of island ecosystems.
  3. Islands as Evolutionary Laboratories: Over 70% of recorded extinctions since 1500 have occurred on islands, underscoring their vulnerability and unique evolutionary pressures.

Conservation Applications

  • Design of Nature Reserves: Insights into minimum viable habitat size and connectivity.
  • Restoration Ecology: Predicting recolonization rates and prioritizing species for protection.
  • Invasive Species Management: Understanding pathways and impacts of non-native species.

Recent Research

A 2022 study by Science Advances found that island biogeography principles apply to urban “green islands” (parks and reserves), with similar patterns of species richness and turnover (Aronson et al., 2022). This expands the theory’s relevance beyond natural islands to fragmented landscapes created by human development.

Most Surprising Aspect

Plastic pollution reaches even the deepest, most remote island and ocean habitats, affecting ecosystems previously thought to be pristine and untouched by human activity. The discovery of microplastics in the Mariana Trench and massive plastic accumulation on Henderson Island exemplifies the global scale and persistence of anthropogenic impacts, challenging previous assumptions about island isolation and ecosystem integrity.

References

  • Lavers, J.L., et al. (2020). “Plastic pollution in the South Pacific subtropical gyre.” Nature Scientific Reports, 10, 10117. Link
  • Peng, X., et al. (2020). “Microplastics in the deepest ocean.” Science of the Total Environment, 703, 134799. Link
  • Aronson, M.F.J., et al. (2022). “Urban island biogeography.” Science Advances, 8(4), abj9933. Link

Summary Table

Factor Effect on Biodiversity Example
Island Size ↑ Size → ↑ Species Madagascar vs. Seychelles
Isolation ↑ Distance → ↓ Immigration Galápagos vs. Caribbean
Human Impact ↑ Pollution/Invasion → ↓ Native Species Henderson Island

Further Reading

  • MacArthur, R.H. & Wilson, E.O. (1967). The Theory of Island Biogeography. Princeton University Press.
  • Whittaker, R.J., et al. (2017). “Island biogeography: Taking the long view.” Ecography, 40(1), 17-27.

End of Study Notes