WK11: Geographic or Global Ecology: Part 2

Nested Subsets

  • Developed by Bruce Paterson.
  • Considers species differ in mobility and vulnerability to local extinction.
  • Related to colonization and extinction.
  • Formative in conservation biology since the 1980s.
  • Part of landscape ecology, understanding species movement and colonization.
  • Measures the order of communities; more nested systems are more organized.
  • Originated from island zoogeography.
  • Used more in conservation biology to understand system structure after human disturbance.
  • Sea level rise isolates islands, leading to species relaxation through local extinction events.

Graphical Demonstration

  • Mountains become isolated patches as sea levels rise, altering species composition.

Island Size and Species

  • Large islands host more species.
  • Medium islands host fewer species.
  • Small islands host even fewer species.

Species Area Relationship

  • Species composition simplifies as island size decreases.
  • Some species are better suited for small islands.
  • Example: Perfect Nesting vs. Observed Patterns
  • Perfect nesting is rare due to ecological variability.
  • Observed patterns show outliers and gaps within the nested subset structure.

Occurrence Matrix

  • Represented as 1 for presence and 0 for absence.
  • Allows for statistical analysis.
  • Shows species on all island sizes versus only small islands.
  • Accounts for holes and outliers due to ecological noise.

Real-World Application

  • Study in North Central Victoria: patch sizes of remnant native vegetation in agricultural landscapes.
  • Considers patch area and its influence on reptile distribution.
  • Different species occur across different patch sizes.
Examples:
  • Marethia skink: found in most patches.
  • Shingleback: found in most patches.
  • Blue tongue and jackalizard: found only in very large patches.
  • Conservation Implications
  • Informs decisions about species under threat and which patches to retain/restore.
  • Large patches are needed to conserve blue tongue lizards, dragons, and goannas.
  • Marethia skinks and shinglebacks are less threatened by landscape structure.
  • Nested subsets provide a narrative around patch area and reptile distribution.

Comparison to Island Biogeography

  • Species identities matter in nested subsets, unlike dynamic equilibrium theory and species area relationships.
  • Focus is on current status and management, not dynamic equilibrium.

Use in Conservation Biology

  • Considers effects of habitat reduction and fragmentation.
  • Guides selection of intact areas for preservation.
  • Informs restoration of landscapes by strategically adding patches.

Latitudinal Gradients

  • Species richness varies with latitude, typically declining away from the Equator.
  • Species richness decreases with distance from the Equator for many animal and plant taxa.
  • Mammal Species Richness in North America
  • Ranges from 15 species in the far north to 150 species in Central America.
  • Plant Species Richness and Latitude
  • Decreases with increasing latitude.
  • Example: 10,000 square kilometer area shows decreasing species count at higher latitudes.

Bird Species Richness and Latitude

  • Tropics can exceed 1,000 species.
  • Polar regions may have fewer than 50 species.
  • Possible Explanations
  • More land area available in tropics.
  • More time for diversification due to continuous landmass.
  • Higher speciation rates or lower extinction rates in tropics.

Productivity and Climate

  • Higher temperatures in tropics drive productivity.
  • Higher Energy Input : More energy in the tropics compared to higher latitudes drives productivity.
  • Annual Evapotranspiration
  • Measures water movement from land to atmosphere through evaporation and transpiration.
  • Higher evapotranspiration correlates with higher tree species richness.
  • Annual evapotranspiration is higher in tropics due to warmth and productivity.

Vertebrates

  • Similar pattern with higher potential evapotranspiration correlating with higher species richness.

Key Points

  • Latitudinal gradients of species richness exist.
  • Tropics are more productive due to abiotic inputs.
  • Nested subsets provide insights for conservation biology.

Exam Questions

  • Understand nested subsets and their applications.
  • Understand latitudinal gradients and their potential drivers.