Speciation and Macroevolution

Biological Species Concept

Defines a species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring.

Viable

Refers to offspring that can live to adulthood.

Fertile

Refers to offspring that are capable of producing their own offspring.

Reproductive Isolation

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

Prezygotic Barriers

Barriers that block fertilization from occurring.

Postzygotic Barriers

Barriers that prevent the hybrid fertilized egg from developing into a viable, fertile adult.

Allopatric Speciation

Speciation that occurs when gene flow is interrupted due to geographical isolation of populations.

Sympatric Speciation

Speciation that occurs in populations that live in the same geographic area and are not physically separated.

Polyploidy

The presence of extra sets of chromosomes due to accidents during cell division.

Cladogram

A branching tree diagram that represents evolutionary relationships among organisms.

Phylogenetic Tree

A branching diagram that shows evolutionary relationships and the time scale of changes.

Homology

A phenotypic or genetic similarity between species due to shared ancestry.

Maximum Parsimony

The principle that the most likely phylogenetic tree is the one that requires the fewest evolutionary events.

Common Ancestor

A species of organism from which one or more new species evolve.

Habitat Isolation

A prezygotic barrier where two species encounter each other rarely because they occupy different habitats.

Temporal Isolation

A prezygotic barrier where species breed at different times, preventing gametes from mixing.

Behavioral Isolation

A prezygotic barrier where courtship rituals unique to a species prevent mating.

Gametic Isolation

A prezygotic barrier where sperm of one species cannot fertilize eggs of another species.

Reduced Hybrid Viability

A postzygotic barrier where hybrid offspring fail to develop or survive.

Reduced Hybrid Fertility

A postzygotic barrier where hybrids are sterile and cannot produce offspring.

Hybrid Breakdown

A postzygotic barrier where first-generation hybrids are fertile, but their subsequent offspring are weak or sterile.

Morphological Species Concept

Defines a species based on its structural features.

Ecological Species Concept

Views a species in terms of its ecological niche.

Phylogenetic Species Concept

Defines a species as the smallest group of individuals that share a common ancestor.