allopatric speciation

Speciation that occurs when populations of the same species become
geographically isolated, often due to dispersal or vicariance.

allopatry

Condition in which two or more populations live in different
geographic areas.

allopolyploidy

(adjective: allopolyploid) The state of having more than two full
sets of chromosomes (polyploidy) due to hybridization between
different species

autopolyploidy

(adjective: autopolyploid) The state of having more than two full
sets of chromosomes (polyploidy) due to a mutation that doubled the
chromosome number. All the chromosomes come from the same species.

biological species concept

The definition of a species as a population or group of populations
that are reproductively isolated from other groups. Members of a
species have the potential to interbreed in nature to produce viable,
fertile offspring but cannot interbreed successfully with members of
other species.

cryptic species

A species that cannot be distinguished from similar species by easily
identifiable morphological traits.

hybrid zone

A geographic area where interbreeding occurs between two species,
sometimes producing fertile hybrid offspring.

morphospecies concept

The definition of a species as a population or group of populations
that have measurably different anatomical features from other groups.
Also called morphological species concept. Compare with biological
species concept and phylogenetic species concept.

niche

The range of resources that a species can use and the range of
conditions that it can tolerate. More broadly, the role that species
plays in its ecosystem.

phylogenetic species concept

The definition of a species as the smallest monophyletic group in a
phylogenetic tree.

polymorphic species

A species that has two or more distinct phenotypes in the same
interbreeding population at the same time.

polyploidy

(adjective: polyploid) The state of having more than two full sets of
chromosomes, either from the same species (autopolyploidy) or from
different species (allopolyploidy).

postzygotic isolation

Reproductive isolation resulting from mechanisms that operate after
mating of individuals of two different species occurs. The most common
mechanisms are the death of hybrid embryos or reduced fitness of hybrids.

prezygotic isolation

Reproductive isolation resulting from any one of several mechanisms
that prevent individuals of two different species from mating.

reinforcement

In evolutionary biology, the natural selection for traits that
prevent interbreeding between recently diverged species.

sister species

Closely related species that occupy adjacent branches in a
phylogenetic tree.

species

An evolutionarily independent population or group of populations.
Generally distinct from other species in appearance, behavior,
habitat, ecology, genetic characteristics, and so on.

subspecies

A population that has distinctive traits and some genetic differences
relative to other populations of the same species but that is not
distinct enough to be classified as a separate species.

sympatric speciation

The divergence of populations living within the same geographic area
into different species as the result of their genetic (not physical)
isolation. Compare with allopatric speciation.

sympatry

Condition in which two or more populations live in the same
geographic area, or close enough to permit interbreeding.

synapomorphy

A shared, derived trait found in two or more taxa that is present in
their most recent common ancestor but is missing in more distant
ancestors. Useful for inferring evolutionary relationships.

vicariance

The physical splitting of a population into smaller, isolated
populations by a geographic barrier.