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adaptive radiation
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.
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adaptive zones
A set of different niches that become be filled by a group of species.
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allopatric speciation
[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.
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anagenesis
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.
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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.
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clade
[Gk. klados-, branch] All species that share a unique trait, being descended from an ancestral species in which the trait first evolved.
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cladogenesis
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.
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cladograms
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.
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derived trait
A novel feature shared only by descendants of an ancestral species in which it originated.
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evolutionary trees
A treelike diagram in which each branch point represents a divergence from a shared ancestor; each branch is a separate line of descent.
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extinction
Irrevocable loss of a species.
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gene flow
Microevolutionary process; alleles enter and leave a population by immigration and emigration. Counters mutation, natural selection, and genetic drift, hence reproductive isolation.
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genetic divergence
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.
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genus, genera
[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.
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gradual model of speciation
Addresses the rate of speciation and cites fossil evidence that morphological changes accumulate slowly over great time spans.
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higher taxa
One of ever more inclusive groupings of species; e.g., family, order, class, phylum, kingdom.
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key innovation
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.
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macroevolution
Large-scale patterns, rates of change, and trends among lineages.
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mass extinctions
Catastrophic event or phase in geologic time when families or other major groups are lost.
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monophyletic group
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.
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niche
[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.
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parapatric speciation
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.
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polyploidy
A case of somatic cells having three or more of each type of chromosome characteristic of the species.
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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.
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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.
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speciation
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.
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species
[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.
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sympatric speciation
[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.
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taxon
A set of organisms of a given type.
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taxonomy
Field of biology that identifies, names, and classifies species.
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three-domain system
A classification system that groups all organisms into domains Bacteria, Archaea, and Eukarya.
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