Speciation by Splitting of Pre-existing Species
Definition
Speciation
Speciation is the evolutionary process through which one species splits into two or more distinct species.
- Speciation is a primary driver of biodiversity, increasing the variety of life.
- It requires reproductive isolation, which allows populations to evolve separately.
- Speciation is distinct from gradual changes within a single species.
- It specifically involves the formation of new species.
Mechanisms of Speciation: The Role of Reproductive Isolation
1. Geographical Isolation (Allopatric Speciation)
- Allopatric speciation occurs when populations are physically separated by barriers such as mountains, rivers, or oceans.
- These barriers prevent interbreeding, allowing populations to evolve independently.
Example: Lava Lizards of the Galápagos Islands
- Lava lizards on the Galápagos Islands are a classic example of allopatric speciation.
- A single species initially colonized the islands, but geographical isolation between the islands prevented interbreeding.
- Over time, genetic drift and natural selection caused the populations on each island to diverge, resulting in multiple unique species.
2. Behavioral or Temporal Isolation (Sympatric Speciation)
- In sympatric speciation, populations live in the same geographical area but become reproductively isolated due to:
- Behavioral Isolation: Differences in mating preferences or courtship behaviors.
In Lake Massoko, two populations of cichlid fish prefer different habitats (shallow vs. deep water), choosing mates based on specific traits.
- Temporal Isolation: Differences in breeding seasons or times.
Winter pine processionary moth populations in Portugal breed during different months, preventing interbreeding.
NoteSympatric speciation is less common than allopatric speciation but demonstrates how species can diverge without physical barriers.
The Process of Speciation: A Step-by-Step Breakdown
1. Separation of Populations:
- Populations become isolated, either:
- Geographically (e.g., rivers, mountains, or islands).
- Reproductively (e.g., differences in behavior or timing).
2. Independent Evolution
- Isolated populations experience different selection pressures, such as:
- Climate changes.
