∞ generated and posted on 2016.08.21 ∞
Collection of organisms all of which belong to the same species.
Members of the same species tend to be highly similar genetically, share genes much more readily among themselves than they do with other populations, and tend to compete directly for a shared set of resources.
Generally when you hear term population you should be thinking, "One species", whereas when more than one species is present within an environment then the group collectively consists of multiple populations (see, then, instead community).
Typically the individual organisms making up a population are considered to be interbreeding, though this criterion can be problematic when defining clonal populations. Note that one may also refer to the clonally related cells making up a multicellular organism as a population of cells and, in viewing multicellular organisms as on an evolutionary continuum with microorganisms, this perspective is both reasonable and consistent with its use referring to populations of free-living cells.
On the other hand, each concept of population as a group of similar and/or clonally related cells is arguably somewhat different from the idea of a population of multicellular organisms since, if nothing else, the two meanings of population refer to different levels of selection.