Knowra Species problem Species problem The difficulty of defining species with one criterion that works for all organisms. Different species concepts classify organisms by reproduction, ancestry, ecology, or observable traits, and can disagree.
Biological species concept : A species concept that defines species as groups of actually or potentially interbreeding natural populations reproductively isolated from others. Its reproductive criterion fits many animals but fails for fossils, asexual organisms, and hybridizing populations.
Speciation : The evolutionary process by which populations become distinct species. It generates the divergence that species criteria attempt to detect.
Microbial taxonomy : The classification and naming of microorganisms using genetic, physiological, ecological, and other evidence. Most microbes reproduce asexually, so taxonomists cannot rely on interbreeding to delimit their species.
Biodiversity : The variety of life, including diversity within species, between species, and among ecosystems. Changing species boundaries changes estimates of how much biological diversity exists.
Phylogenetic species concept : A species concept that treats species as the smallest diagnosable, historically distinct lineage on a phylogenetic tree. Its lineage-based criterion can divide populations that other species concepts group together.
Reproductive isolation : The reduction or cessation of gene flow between populations through barriers to mating or reproduction. It supports biological species boundaries, though it is incomplete or irrelevant in many organisms.
Paleontology : The study of ancient life through fossils and other traces of past organisms. Fossil species must often be distinguished by morphology because reproductive behavior is unavailable.
Taxonomy : The science of naming, describing, and classifying organisms. Species concepts guide the decisions through which taxonomists organize life.
Morphological species concept : A species concept that distinguishes species by consistent differences in form and structure. Its observable criteria work with fossils but can miss cryptic species and vary within a species.
Gene flow : The transfer of genetic variants between populations through migration and reproduction. Ongoing exchange can blur boundaries even when populations differ in form or ecology.
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