Species and Speciation Quiz

Study Notes

Species are groups of organisms with similar features that can interbreed and produce viable, fertile offspring.
Speciation is the process of species formation from an existing species.
Two main mechanisms of speciation are allopatric and sympatric.

Defines a species as a group that can interbreed under natural conditions and produce fertile offspring.
Assumes common characteristics, genetic compatibility/common ancestry and sexual reproduction.

Cannot be applied to exclusively asexual organisms (prokaryotes, amoeba, some protists, and some animals, plants, and fungi).
Difficult to assess interbreeding in isolated populations (e.g., can a deer in Portland interbreed with one in Westmoreland, or can a Great Dane interbreed with a Chihuahua?).
Some species look and behave differently but can interbreed and produce viable, fertile offspring (e.g., coyotes, wolves, and dogs).
Fossil organisms' interbreeding capabilities are difficult to determine, and gene comparison across fossil species is usually impossible.

Reproductive isolating mechanisms are barriers between species that prevent viable, fertile offspring.
Prezygotic mechanisms occur before fertilization. Examples include geographic isolation, temporal isolation, habitat isolation, and behavioral isolation.
Postzygotic mechanisms occur after fertilization. Examples include reduced hybrid viability, reduced hybrid fertility, and hybrid breakdown.

Geographic isolation: Populations are separated by geographical barriers (e.g., mountains, rivers, oceans).
Temporal isolation: Populations breed at different times of the day, seasons, or years (e.g., eastern and western spotted skunks).
Habitat isolation: Populations live in different habitats within the same geographic area but do not encounter each other (e.g., water-dwelling and terrestrial snakes).
Behavioral isolation: Populations have different courtship rituals that prevent mating (e.g., blue-footed boobies, Eastern and Western meadowlarks).

Reduced hybrid viability: Hybrid zygotes fail to develop or reach sexual maturity.
Reduced hybrid fertility: Hybrids are sterile (e.g., mules).
Hybrid breakdown: First-generation hybrids may be fertile, but later generations have reduced viability or fertility (e.g., some plant hybrids).

Speciation that occurs when populations are geographically separated.
Geographic separation prevents gene flow and leads to genetic divergence and reproductive isolation.