Bio1151 Chapter 24 Lec 20

Speciation

An evolutionary process in which one species splits into two or more species.

Macroevolution

The broad pattern of evolution above the species level.

Species (Biological Species Concept)

A population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring but do not produce viable, fertile offspring with members of other such groups.

Hybrids

Offspring that result from the mating of individuals from two different species or from two true-breeding varieties of the same species.

Niches

The “role” a species plays in a complex ecosystem/habitat.

Adaptive Radiation

Periods of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill different ecological roles in their communities.

Reproductive Isolation

The existence of biological factors (barriers) that impede members of two species from producing viable, fertile offspring.

Types of Reproductive Barriers

1. Prezygotic

2. Postzygotic

Prezygotic Barriers

Reproductive barriers that impede mating between species or hinders fertilization if interspecific mating is attempted.

Five different types.

Types of Prezygotic Barriers

1. Habitat Isolation

2. Behavioral Isolation

3. Temporal Isolation

4. Mechanical Isolation

5. Gametic Isolation

Habitat Isolation

Two organisms that use different habitats (even in the same geographic area) are unlikely to encounter each other to even attempt mating.

Behavioral Isolation

Species use unique and elaborate courtship behaviors to attract mates.

Temporal Isolation

Two species that breed during different times of day, different seasons, or different years cannot mix gametes.

Mechanical Isolation

Closely related species may attempt to mate but fail because they are anatomically incompatible and transfer of sperm is not possible.

Gametic Isolation

The gametes of two species do not form a zygote because of incompatibilities preventing fertilization.

Postzygotic Barriers

Reproductive barriers that prevent hybrid zygotes produced by two different species from developing into viable, fertile adults.

Three different types.

Types of Postzygotic Barriers

1. Reduced Hybrid Viability

2. Reduced Hybrid Fertility

3. Hybrid Breakdown

Reduced Hybrid Viability

Genetic incompatibility between the two species may abort the development of the hybrid at some embryonic stage or produce frail offspring.

Reduced Hybrid Fertility

Even if the hybrid offspring are vigorous, the hybrids may be infertile, and the hybrid cannot back-breed with their parental species.

Hybrid Breakdown

First-generation hybrids are viable and fertile. When first-generation hybrids mate with either parent species or with each other, however, the next generation is feeble or sterile.

Types of Speciation

1. Allopatric Speciation

2. Sympatric Speciation

Allopatric Speciation

The formation of new species in populations that are geographically isolated from one another.

Sympatric Speciation

The formation of new species in populations that live in the same geographic area.

Punctuated Equilibrium

In the fossil record, long periods of apparent stasis, in which a species undergoes little or no morphological change, interrupted by relatively brief periods of sudden change.