Nonadaptive radiations are a subset of
evolutionary radiations (or
species 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 by
nonecological speciation.[2][4] In many cases, this nonecological speciation is
allopatric, 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 the
Mediterranean[1] and Batrachosepssalamanders from
California[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 certain
damselflies[3] and
crickets from
Hawaii,[5] there can be range overlap in closely related species, and it is likely that
sexual selection (and
species recognition) plays a role in maintaining (and perhaps giving rise to) species boundaries.[4]