Nonadaptive radiations are a subset ofevolutionary radiations (orspecies flocks) that are characterized by diversification that is not driven by resource partitioning.[1][2][3][4] The species that are a part of a nonadaptive radiation will tend to have very similar niches, and in many (though not all) cases will be morphologically similar.[4] Nonadaptive radiations are driven bynonecological speciation.[2][4] In many cases, this nonecological speciation isallopatric, and the organisms are dispersal-limited such that populations can be geographically isolated within a landscape with relatively similar ecological conditions.[4] For example,Albinaria land snails on islands in theMediterranean[1] andBatrachosepssalamanders fromCalifornia[2] each include relatively dispersal-limited, and closely related, ecologically similar species often have minimal range overlap, a pattern consistent with allopatric, nonecological speciation. In other cases, such as certaindamselflies[3] andcrickets fromHawaii,[5] there can be range overlap in closely related species, and it is likely thatsexual selection (andspecies recognition) plays a role in maintaining (and perhaps giving rise to) species boundaries.[4]
