Species, populations and strains

A species can encompass many biological populations. A biological population specifies a set of organisms in a place and time; a biological strain identifies a maintained variant or lineage, often in a laboratory. A species name, a local census and a biological strain designation therefore describe different things. Multiple independently maintained cultures can also share the same biological strain designation.

For example, a culture identified as Escherichia coli K-12 MG1655 specifies more than the species alone. Two flasks inoculated from that culture are separate experimental biological populations; the separate containers do not establish two species or two different biological strains. This is an original experimental bookkeeping example, not a claim that every biological strain name encodes a complete genotype.