Species and Speciation

Species (biological species concept)

a group of populations that can interbreed in nature and produce fertile offspring.

Speciation

formation of a new species from an ancestral population.

Allopatric speciation

new species form when populations are geographically isolated.

Sympatric speciation

new species form in the same area due to ecological, behavioral, or genetic differences.

Reproductive isolation

barriers that prevent different populations from producing fertile offspring.

Prezygotic isolation (before fertilization)

prevents mating or fertilization.

Habitat isolation

live/breed in different environments.

Temporal isolation

reproduce at different times (day, season, year).

Behavioral isolation

different mating rituals or behaviors.

Mechanical isolation

incompatible reproductive anatomy.

Gametic isolation

sperm and egg cannot fuse.

Postzygotic isolation (after fertilization)

fertilization occurs, but offspring are not viable/fertile.

Hybrid inviability

zygote/embryo does not develop properly.

Hybrid infertility (sterility)

offspring are sterile (e.g., mule).

Hybrid breakdown

offspring are fertile, but later generations become weak or sterile.