Temporal Variability of Abundance and the Distribution of Species

Abstract

The geographic range size of congeneric species of rodents and noctuid moths is positively correlated with the amplitude of fluctuation of their local populations. This result is explained by two complementary hypotheses. First, selective species extinction may preferentially weed out small-ranging species with large population fluctuations because they should be shorter-lived than comparably restricted species with stable population levels. Second, compared with allied species occupying small areas, widespread species may be selected at the individual level to have relatively opportunistic life histories enabling them to exploit relatively unstable resources and habitats. This two-part interpretation makes two testable predictions which are confirmed by numerous cited literature reports: (1) wide-ranging species should more often be found in disturbed, ephemeral, or strongly seasonal habitats than their narrowly distributed relatives, and (2) widespread species should have higher reproductive potentials than their restricted congenerics. Several ecological and evolutionary implications of these findings are discussed, including their possible bearing on the controversial problem of evolutionary stasis.