Study Notes on Island Biogeography and Ecological Tolerance

Theory of Island Biogeography

Island Characteristics

  • The larger the island, the greater the ecosystem diversity.

  • Greater ecosystem diversity leads to abundant food and habitat resources.

  • More niches or roles are available for organisms within the ecosystem.

  • Larger islands support a higher total number of species.

  • Islands closer to the mainland support more species.

Island Biogeography Defined

  • It encompasses the ecological relationships and community structures on islands, which can include both literal islands and figurative habitat islands (e.g., urban parks).

Basic Rules of Island Biogeography

  1. It is easier for colonizing organisms to travel from the mainland to the island.

  2. A higher number of colonizing organisms leads to more genetic diversity in the new population.

Factors Affecting Species Richness

Larger Islands

  • Positive correlation between island size and species richness:

    • Larger islands support more species due to higher ecosystem diversity.

    • Availability of more niches (e.g., diverse food sources for birds on the Galapagos Islands).

    • Larger populations that are genetically diverse and have higher resilience to environmental disturbances.

    • Lower extinction rates as species are less likely to die off.

Distance from Mainland

  • Closer islands to the mainland have higher species richness:

    • Migration is easier and more frequent, leading to increased genetic diversity and larger populations.

    • There is an inverse relationship between island distance from the mainland and species richness; greater distance results in fewer species.

Evolution on Islands

  • Limited space and resources drive unique evolutionary conditions:

    • Increased pressure for species to adapt to narrower niches.

    • Adaptive Radiation: A single species rapidly evolving into several new species to exploit different resources and reduce competition.

      • Example: Galapagos Finches, which evolved different beak sizes to utilize various food sources on the island.

Ecological Tolerance

Ecological Range of Tolerance

  • Organisms have specific tolerances for environmental conditions:

    • Example: Salmon have a core temperature tolerance range of 6^{ ext{o}} to 22^{ ext{o}}C, yet certain individuals can endure beyond this range due to adaptations.

    • Increased genetic biodiversity boosts the resistance of salmon populations to disturbances such as global warming.

Tolerance Zones

  1. Optimal Range: Conditions where organisms can survive, grow, and reproduce effectively.

  2. Zone of Physiological Stress: Conditions where organisms survive but experience stress (e.g., reduced growth).

  3. Zone of Intolerance: Conditions that lead to death (e.g., thermal shock, suffocation).

Island Characteristics

  • Larger islands have greater ecosystem diversity.

  • This diversity provides more food, habitat, and niches.

  • Larger islands support more species.

  • Islands closer to the mainland support more species.

Island Biogeography Defined

  • Studies ecological relationships and community structures on literal and habitat islands (e.g., urban parks).

Basic Rules of Island Biogeography

  1. Colonization is easier from mainland to island.

  2. More colonizers mean greater genetic diversity in new populations.

Factors Affecting Species Richness

Larger Islands

  • Island size positively correlates with species richness:

    • Larger islands: more species due to greater ecosystem diversity.

    • More available niches (e.g., diverse food sources for Galapagos Finches).

    • Larger, genetically diverse populations are more resilient.

    • Lower extinction rates.

Distance from Mainland

  • Islands closer to the mainland have higher species richness:

    • Easier, frequent migration increases genetic diversity and population size.

    • Inverse relationship: greater distance, fewer species.

Evolution on Islands

  • Limited space and resources drive unique evolution:

    • Species adapt to narrower niches.

    • Adaptive Radiation: A single species rapidly evolves into multiple new species, exploiting diverse resources and reducing competition.

      • Example: Galapagos Finches' varied beak sizes for different food sources.

Ecological Tolerance
Ecological Range of Tolerance

  • Organisms tolerate specific environmental conditions:

    • Example: Salmon's core temperature tolerance is 6^{ ext{o}} to 22^{ ext{o}}C. Some individuals adapt to endure beyond this.

    • High genetic biodiversity increases salmon's resistance to disturbances like global warming.

Tolerance Zones

  1. Optimal Range: Ideal conditions for survival, growth, and reproduction.

  2. Zone of Physiological Stress: Organisms survive under stress (e.g., reduced growth).

  3. Zone of Intolerance: Conditions leading to death (e.g., thermal shock, suffocation).