Species

Definition

The fundamental taxonomic rank and basic unit of biodiversity, conventionally defined as a population or group of populations whose members can interbreed to produce fertile offspring under natural conditions. In practice, species boundaries are assessed through multiple criteria—morphology, genetics, ecology, and behavior—especially for arthropods where cryptic speciation (genetically distinct but morphologically similar lineages) is common. Species names follow binomial nomenclature: a genus name plus a specific epithet (e.g., *Apis mellifera*).

Etymology

From Latin "species" meaning appearance, kind, or sort; used in biological classification since Linnaeus (1753).

Example

The two European honey bee species *Apis mellifera* and *Apis cerana* remain distinct because hybrids are sterile or inviable, whereas populations of *A. mellifera* across its native range constitute one species despite considerable geographic variation.

Synonyms

• specific taxon
• biological species

Related Terms

• Genus
• Subspecies
• Conspecific
• cryptic speciation
• Type specimen
• Binomial nomenclature
• biological species concept
• morphospecies

Usage Notes

The plural "species" is identical to the singular. The biological species concept (interbreeding criterion) is difficult to apply to asexual organisms, fossils, or geographically isolated populations; alternative concepts (phylogenetic, ecological, morphological) are often used in practice. Arachnologists and entomologists frequently encounter species complexes where multiple cryptic species hide under one morphological name, requiring molecular data to resolve.