Chapter 24

• A species is an evolutionarily independent population or group of populations. Generally distinct from other species in appearance, behavior, habitat, ecology, genetic characteristics, and so on.
• A lineage is an evolutionary unit that includes an ancestral population and all of its descendants but no others. Also called a clade or lineage. Compare with paraphyletic group and polyphyletic group.
• Systematics is the subdiscipline of biology that characterizes and classifies the relationships among all organisms on Earth.
• Biogeography is the study of how species and populations are distributed geographically and through geologic time.
• Autopolyploid (adjective: autopolyploid) is 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. Compare with allopolyploidy
• The phylogenetic species concept is the definition of a species as the smallest monophyletic group in a phylogenetic tree. Compare with biological species concept and morphospecies concept.
• Sympatric speciation is 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
• Allopatry is the condition in which two or more populations live in different geographic areas. Compare with sympatry.
• Reinforcement, in evolutionary biology, is the natural selection for traits that prevent interbreeding between recently diverged species.
• Allopolyploid (adjective: allopolyploid) is the state of having more than two full sets of chromosomes (polyploidy) due to the hybridization between species. Compare with autopolyploidy.
• Vicariance is the physical splitting of a population into smaller, isolated populations by a geographic barrier
• Sympatry is the condition in which two or more populations live in the same geographic area, or close enough to permit interbreeding. Compare with allopatry.
• A niche is the range of resources that a species can use and the range of conditions that it can tolerate. More broadly, the role that a species plays in its ecosystem.
• A hybrid zone is a geographic area where interbreeding occurs between two species, sometimes producing fertile hybrid offspring.
• The biological species concept is 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. Compare with morphospecies concept and phylogenetic species concept.
• The morphospecies concept (“form-species”) is 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.
• Speciation is the evolution of two or more distinct species from a single ancestral species.
• Synapomorphy is 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.
• A polymorphic species is a species that has two or more distinct phenotypes in the same interbreeding population at the same time.
• Taxonomy is the branch of biology concerned with describing, naming, and classifying goups of organisms.
• A clade is an evolutionary unit that includes an ancestral population and all of its descendants but no others. Also called a clade or lineage. Compare with paraphyletic group and polyphyletic group.
• Prezygotic isolation is reproductive isolation resulting from any combination of several mechanisms that prevent individuals of two different species from mating.
• Dispersal is the movement of individuals from their place of origin to the location where they live and breed as adults.
• A monophyletic group is an evolutionary unit that includes an ancestral population and all of its descendants but no others. Also called a clade or lineage. Compare with paraphyletic group and polyphyletic group.
• Postzygotic isolation is 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.
• Allopatric speciation is speciation that occurs when populations of the same species become geographically isolated, often due to dispersal or vicariance. Compare with sympatric speciation.
• A cryptic species is a species that cannot be distinguished from similar species by easily identifiable morphological traits.