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allopatric speciation

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

allopolyploid

A fertile individual that has more than two chromosome sets as a result of two different species interbreeding and combining their chromosomes.

autopolyploid

An individual that has more than two chromosome sets that are all derived from a single species.

biological species concept

Definition of a species as 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.

ecological species concept

A definition of species in terms of ecological niche, the sum of how members of the species interact with the nonliving and living parts of their environment.

hybrid

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

hybrid zone

A geographic region in which members of different species meet and mate, producing at least some offspring of mixed ancestry.

macroevolution

Evolutionary change above the species level, including the origin of a new group of organisms or a shift in the broad pattern of evolutionary change over a long period of time. Examples of macroevolutionary change include the appearance of major new features of organisms and the impact of mass extinctions on the diversity of life and its subsequent recovery.

morphological species concept

A definition of species in terms of measurable anatomical criteria.

phylogenetic species concept

A definition of species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life.

postzygotic barrier

A reproductive barrier that prevent hybrid zygotes produced by two different species from developing into viable, fertile adults.

prezygotic barrier

A reproductive barrier that impedes mating between species or hinders fertilization if interspecific mating is attempted.

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.

reinforcement

A process in which natural selection strengthens prezygotic barriers to reproduction, thus reducing the chances of hybrid formation. Such a process is likely to occur only if hybrid offspring are less fit than members of the parent species.

reproductive isolation

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

speciation

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

species

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.

sympatric speciation

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

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