Chapter 22 -Lecture

Chapter 22 Geographic Ecology

22.1 Species Richness and Geographic Patterns

• Species Area Relationship: Species richness increases with area and decreases with isolation.

• Dynamic Immigration-Extinction Balance: Species richness can be modeled as a balance between immigration and extinction.

• Latitudinal Patterns: Species richness generally increases from middle and high latitudes toward the equator.

• Influence of Historical Processes: Long-term historical and regional influences affect species richness and biodiversity.

Introduction to Geographic Ecology

• Definition: Geographic ecology seeks to map the patterns of plant and animal life.

• Focus Areas: Primarily concentrates on island biogeography, latitudinal patterns in species richness, and the influence of historical processes on biodiversity.

22.1 Area and Isolation Effects on Species Richness

• Early Contributions: Arrhenius quantitated the relationship between area and species number; a foundation for geographic ecology.

Island Area and Species Richness

• Preston's Findings: Noted that the fewest bird species exist on the smallest islands, while the largest islands host the most species.

• Nilsson et al.: Identified island area as a key predictor of species richness among various taxa in Sweden.

Habitat Fragmentation

• Montane Islands: Following warming at the end of the Pleistocene, forests and habitats became fragmented into isolated mountain peaks, impacting both plant and animal distribution.

• Lake Islands: Lakes function as islands with species diversity correlating with lake area studied by Tonn and Magnuson, as well as global studies by Barbour and Brown.

Marine Islands

• MacArthur and Wilson's Findings: Isolation leads to reduced bird diversity on Pacific Islands, with observed increases in diversity with larger island sizes.

22.2 Equilibrium Model of Island Biogeography

• Concept Overview: Introduced by MacArthur and Wilson; species diversity reflects a balance between immigration and extinction rates.

• Immigration Rates: Highest on new islands; declines as species accumulate.

• Extinction Rates: Increase with more species as competition intensifies and species populations diminish.

• Prediction of Species Number: Point of intersection of immigration and extinction rates predicts the expected number of species on an island, influenced by both island size and distance from source populations.

Species Turnover

• Dynamic Composition: Species composition changes over time, known as species turnover; Diamond's studies on California Channel Islands illustrated this.

Experimental Studies

• Simberloff and Wilson: Investigated recolonization patterns on defaunated islands, affirming the dynamic nature of species composition.

22.3 Latitudinal Gradients in Species Richness

• General Trend: Species richness increases as one moves from higher latitudes to the equator.

• Hypotheses: Six categories of mechanisms explaining this pattern:

  1. Time Since Perturbation: Tropics have older ecosystems with less disturbance, allowing for higher speciation rates.

  2. Productivity: High energy in the tropics supports larger populations and reduces extinction risks.

  3. Environmental Heterogeneity: Increased habitat complexity in the tropics supports diverse species.

  4. Favorable Climatic Conditions: Less temperature variation and physically extreme environments in the tropics support greater biodiversity.

  5. Niche Breadths and Interactions: Tropical species may be more limited by biological factors than physical.

  6. Speciation and Extinction Rates: The tropics experience higher rates of speciation and lower extinction rates compared to higher latitudes.

Area's Role in Species Richness

• Regional Area Influence: Larger land areas in the tropics allow for more habitat diversity, which supports greater species richness.

22.4 Historical and Regional Influences on Species Richness

• Exceptional Patterns: Variance in species richness that cannot simply be explained by area, illustrated by the Cape region of South Africa having more species than larger areas like California.

• Historic Factors: Influences such as continental drift and climate changes have historically shaped biodiversity in regions.

• Comparative Biogeographic Studies: The unique historical processes in different temperate regions lead to varying levels of biodiversity despite similar areas.

Conclusion

• A comprehensive overview focuses on island biogeography, latitudinal species richness patterns, and historical influences affecting biodiversity, including practical applications in geographic information systems (GIS).