Barrington, David S. .
Dispersal versus Migration of Spores among the Ferns.
A worldwide analysis of geographic distributions in the fern genus Polystichum yields two incongruent patterns: the general restriction of species to intracontinental centers rich in endemic species finds exception in a clear pattern of broad geographic source and low endemism for the species-rich Polystichum flora of Taiwan. The profile of the Taiwan Polystichum flora fits with traditional ideas arguing frequent long-distance dispersal and low endemism due to high dispersibility of fern spores. However, under this scenario there should be a general tendency to broad distribution and low endemism in Polystichum; instead we see frequent endemism to intracontinental centers of diversity. In contrast to the continental centers of endemism, Taiwan is strikingly young (4 myr) geologically though it has attained an elevation of 4000 m. As a result, throughout its brief history, Taiwan has presented newly opening habitats and high levels of ecological disturbance. Taiwan's rich species diversity argues for frequent successful migration, presumably related to the abundance of open habitats. In contrast, ecological niches in endemic centers may be largely occupied, making successful long-distance dispersal (i.e. migration) less likely. Reflecting on the pattern encountered in Taiwan polystichums evokes another set of broad distributions, the circumboreal. The striking absence of endemism among ferns in the North is correlated with extensive recent range expansion into terrain characterized by chaotic ecological disturbance. Conversely, the austral regions — rich in ancient terrains and characterized by climatic stability — are rich in endemic species, at least in Polystichum. Together, these observations support the contention that, just as in angiosperms, long-distance migration is limited by ecological exclusion as well as by propagule dispersibility.
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1 - University of Vermont, Plant Biology Department, Marsh Life Sciences Bldg, 109 Carrigan Drive, Burlington, Vermont, 05405-0086, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 28th, 2008
Time: 11:00 AM