L04a_Speciation (1)

Speciation Overview

• Species Name:

  • A. harrisii (North Rim)

  • A. leucurus (South Rim)

Causes of Evolutionary Change

• Microevolution: Evolution on a population level caused by various processes.

• Macroevolution: Long-term evolutionary changes leading to speciation.

Evolutionary Processes

• Macroevolution: Represents evolutionary change on a grand scale leading to large differences, such as the emergence of new phyla.

  • Involves the process of one species splitting into multiple species (speciation).

• Microevolution: Refers to evolution that occurs in populations over shorter time scales.

  • Examples include changes in house sparrow populations across different environments.

Definitions of Species and Speciation

• Speciation: The process whereby one species splits into two or more species.

• Biological Species Concept: A species is defined as individuals that can potentially interbreed and produce fertile offspring.

  • Reproductive barriers that prevent mating or fertilization.

  • Barriers may also lead to sterile offspring.

Mechanisms of Speciation

• Preventing Gene Flow: Both allopatric and reproductive barriers must exist to define distinct species.

  • Physical barriers (geographic) are crucial in preventing gene flow between populations.

Preventing Gene Flow & Its Impact

• Gene Flow: The movement of genes among populations through interbreeding.

• Increased gene flow leads to similarities between populations; reduced flow fosters distinct species.

Allopatric Speciation

• Involves the separation of populations by a physical barrier that disrupts gene flow.

  • Most common form of speciation.

  • Isolated populations focus on genetic differences accumulating via genetic drift, mutation, and natural selection.

  • Over time, these genetic differences contribute to reproductive isolation.

Examples of Geographic Barriers

• Geographic barriers can affect different species differently based on their dispersal abilities:

  • Mountains: Serve as barriers for wild equines (e.g., horses and donkeys).

  • Rivers: Act as barriers for specific species, such as beetles.

  • Sandbars: Function as barriers for aquatic species like fish.

Habitat Islands

• Definition: Areas of hospitable habitat separated by inhospitable regions where species cannot easily disperse:

  • Examples of geographical isolation include:

    • Woodlots or forest fragments amid cropland.

    • Ponds or lakes surrounded by land.

    • Mountain tops isolated by lowlands.

    • Vegetated parks interspersed within urban settings.

• Only species unable to easily traverse between islands may be significantly affected by these geographical partitions.