Diversification

Key Concepts in Biogeography

• Biogeography: Study of the distribution of species and ecosystems in geographic space and time

• Bioregions:

  • Defined by natural ecological characteristics such as plant and animal species and ecosystems.

  • Example: Areas are categorized based on ecological traits rather than arbitrary political boundaries.

• Bioregionalization:

  • Involves creating classifications of the biosphere based on natural areas.

  • Suggests that political and economic systems function better when aligned with these naturally defined regions.

Ecological Factors Impacting Biogeography

• Ecological Factors:

  • Highly non-random influences on distributions, including both physical (abiotic) and biotic components.

  • Organismal time scales range from seconds to decades, while geological events span millions of years.

  • Important physical influences: Tectonics, oceanic and atmospheric circulation, climate changes, and Pleistocene sea-level variations.

Geographic Patterns of Species Richness

• Net Rate of Diversification: Defined by the equation
  $D = S - E$

  • Where:

  • $S$ = rate of speciation

  • $E$ = rate of extinction

• Generalists vs. Specialists:

  • Generalists:

  • Low rates of speciation and extinction

  • Specialists:

  • High rates of both

• Latitudinal Species Gradient:

  • The relationship between diversity (D) in tropical versus extratropical regions

  • Expressed as:
    $D = S - E + I$

  • Where $I$ = rate of immigration

  • Patterns indicate tropical regions have greater biodiversity.

Endemism and Extinction

• Endemism:

  • Differentiation occurs based on hierarchy in both space and time.

  • Examples:

  • Neoendemic: species currently differentiated in their current location

  • Paleoendemic: once widely distributed but now restricted

  • Relicts:

  • Remnants of species that were once more widespread, such as Bristlecone pine (Pinus longaeva).

Biogeographic Patterns and Provincialism

• Provincialism:

  • Concept of how distribution patterns of species and ecosystems create distinct geographical regions known as provinces.

  • Biogeographic provinces reflect boundaries based more on ecological characteristics rather than simple geographical proximity.

Disjunct Distributions and Biotic Interchanges

• Disjunct Distributions:

  • Distribution patterns where species are found in widely separated areas, often due to historical land changes or fragmentation

• Biotic Interchanges:

  • Factors eroding barriers between biota can lead to connections (or filters) between previously isolated regions.

  • Example discussed: The Great American Biotic Interchange (GABI).

Earth History Events and Their Impact

• Earth history events influence biodiversity through two primary processes:

  • Vicariance: The formation of barriers separating biotic communities.

  • Geodispersal: The removal of barriers allowing species to mix across former boundaries.

  • Example: Tectonic shifts influencing drainage patterns.

• Future classes will focus on dispersed values and the ongoing evolution of biogeographic understanding.