A population is said to be locally adapted if organisms in that population have differentially evolved as compared to other populations within their species in response to selective pressures imposed by some aspect of their local environment, be that aspect biotic or abiotic. Therefore, Local adaptation is simply when a population of organisms has evolved to be more well-suited to its environment than other members of the same species. Local adaptation is often determined via reciprocal transplant experiments, where organisms from one population are transplanted into another population, and vice versa, and their finesses measured. If the transplanted organisms have lower fitness in the novel environment, than the native population can be said to be locally adapted.
Populations located in different environments may be faced with different biotic and abiotic pressures, consequently natural selection may drive the evolution of these populations in different directions. This divergent natural selection can lead to differences in trait values among populations for those traits that are heritable and impact organism fitness. Local adaptation of a variety of traits has been demonstrated in numerous, phylogenetically disparate organisms.
Examples of local adaptation abound in the natural world. For instance, many plant populations exhibit local adaptation. This has been established by reciprocally transplanting plants from one population into another population, and vice versa. The transplanted plants often do worse in the novel environment, than their conspecifics that are locally adapted. Many examples of local adaptation exist in host-parasite systems as well. For instance, a host may be resistant to a locally-abundant pathogen or parasite, but conspecific hosts from elsewhere where that pathogen is not abundant may have no evolved no such adaptation. -