Study Notes on Island Biogeography and Conservation

Robert MacArthur and Edward O. Wilson: Islands and Evolution

  • Endemism

    • Definition: A term used to describe species that are found in only one specific location.

    • Islands are notable for having a high number of endemic species.

  • Cosmopolitan Species

    • Definition: Species that are found worldwide.

    • Example: Seagulls, which can inhabit various regions across the globe.

Island Biogeography and Conservation

  • Habitat Fragmentation

    • Observation: The size of a habitat influences its biodiversity.

    • General Rule: The larger the habitat, the better it is for maintaining greater diversity.

  • SLOSS Debate

    • Acronym Meaning: Single Large Or Several Small?

    • Discussion on whether conserving a single large habitat area is more beneficial for biodiversity than conserving multiple smaller areas.

  • Edge Effects

    • Definition: Changes in population or community structures that occur at the boundaries of two or more habitats.

    • Ecotone: A transition area between two ecosystems that often boasts a diverse community of species.

    • Positive Edge Effect: Certain environments, like intertidal zones, demonstrate increased biodiversity and ecological interaction at their borders.

    • Downsides of Edges:

    • Smaller islands or fragmented habitats tend to have more edge, which can negatively impact species.

    • Example: Nesting birds that inhabit forests may face risks from brood parasitism.

      • Specific Example: Cowbirds lay their eggs in the nests of other species like the wood thrush, leading to decreased reproductive success for the host species.

      • Result: The “forest island” may become insufficiently sized for the wood thrushes to thrive due to excessive edge effects.

Connectivity Between “Islands”

  • Increased connectivity (or linkage) among smaller islands can enhance immigration rates, supporting species diversity.

  • Observation: When islands are smaller, higher connectivity can lead to improved ecological interaction and species flow among habitats.

Quiz Preparation

  • Key Concept to Understand:

    • Differentiate between Species Diversity and Species Richness.

    • Diversity: Represents the number of different species present in a given area, as well as their proportional representation within that area.

    • Richness: Refers solely to the number of different species, without considering their proportions or abundance.