A macroevolutionary pattern. A burst of genetic divergences from a lineage that gives rise to many species, each able to use a novel resource or to move into a new, or newly vacated, habitat.
A set of different niches that become be filled by a group of species.
[Gk. allos, different, + L. patria, native land] Speciation model. A physical barrier arises and separates populations or subpopulations of a species, ends gene flow, and so favors divergences that result in new species.
A major pattern of speciation. Directional changes in allele frequencies and morphology are confined within a single lineage, and in time a new type differs so much from the ancestral type that it is classified as a separate species.
biological species concept
Definition of a sexually reproducing species as one or more populations of individuals that interbreed under natural conditions, produce fertile offspring, and are reproductively isolated from other such populations.
[Gk. klados-, branch] All species that share a unique trait, being descended from an ancestral species in which the trait first evolved.
One speciation pattern. A lineage branches when one or more of its populations or subpopulations become reproductively isolated, and then genetic divergences result in new species.
Evolutionary tree diagram that depicts relative relatedness among groups. Each branch is monopyletic; it includes only an ancestral species in which a unique trait first evolved and all of its descendants.
A novel feature shared only by descendants of an ancestral species in which it originated.
A treelike diagram in which each branch point represents a divergence from a shared ancestor; each branch is a separate line of descent.
Irrevocable loss of a species.
Microevolutionary process; alleles enter and leave a population by immigration and emigration. Counters mutation, natural selection, and genetic drift, hence reproductive isolation.
An accumulation of differences in the gene pools of two or more populations or subpopulations of a species after gene flow stops entirely; mutation, natural selection, and genetic drift operate independently in each one.
[L. genus, race or origin] A grouping of species more closely related to one another in morphology, ecology, and history than to others at the same taxonomic level.
gradual model of speciation
Addresses the rate of speciation and cites fossil evidence that morphological changes accumulate slowly over great time spans.
One of ever more inclusive groupings of species; e.g., family, order, class, phylum, kingdom.
A chance modification in some body structure or function that gives a species the opportunity to exploit the environment more efficiently or in a novel way; e.g., modifications of the forelimbs of amniotes into diverse legs and wings during radiations into adaptive zones.
Large-scale patterns, rates of change, and trends among lineages.
Catastrophic event or phase in geologic time when families or other major groups are lost.
A set of species that share a derived trait, a novel feature that evolved in one species and is present only in its descendants; all of the evolutionary branchings from a single stem.
[L. nidas, nest] Sum total of all activities and relationships in which individuals of a species engage as they secure and use the resources required to survive and reproduce.
A speciation model. Populations in contact along a common border evolve into new species; hybrids that form in the contact zone are less fit than individuals on either side of it and thereby act as a reproductive isolating mechanism.
A case of somatic cells having three or more of each type of chromosome characteristic of the species.
punctuation model of speciation
Addresses the rate of speciation; cites fossil evidence that morphological changes required for reproductive isolation evolve in a relatively brief time span, within the tens to hundreds of thousands of years when two or more populations are diverging from each other.
reproductive isolating mechanisms
Any heritable feature of body form, function, or behavior that prevents interbreeding between two or more populations; sets the stage for genetic divergences.
One of the macroevolutionary processes; formation of daughter species from a population or subpopulation of a parent species; the routes vary in their details and duration.
[L. species, a kind] Of sexually reproducing species, one or more natural populations of individuals that successfully interbreed and are isolated reproductively from other such groups. By a cladistic definition, one or more natural populations of individuals with at least one unique trait derived a common ancestor that occurs in no other groups.
[Gk. sym, together, + patria, native land] A speciation model. Occurs inside the home range of a species in the absence of a physical barrier; e.g., by way of polyploidy in flowering plants.
A set of organisms of a given type.
Field of biology that identifies, names, and classifies species.
A classification system that groups all organisms into domains Bacteria, Archaea, and Eukarya.