SHORT-TERM EVOLUTION OF REDUCED DISPERSAL IN ISLAND PLANT POPULATIONS

1 Dramatic reductions in dispersal potential are characteristic of many diverse taxa, both plants and animals, on oceanic islands. This paper documents the same trend of reduced dispersal ability over the course of just a few generations in some weedy, short-lived and wind-dispersed plants of inshore islands in British Columbia, Canada. 2 We measured dispersal-related morphological characteristics of diaspores from island populations of known ages, and from mainland populations. In two of three species with sufficiently large sample sizes, older island populations show increasingly reduced dispersal potential relative to mainland populations or to young island populations. 3 These and other morphological differences are consistent with results expected from strong selection for reduced dispersal potential, and may be striking examples of short-term evolution in small and isolated natural populations.

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