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Metapopulation dynamics in a natural microcosm.
Lehtinen, Richard*,1, 1 University of Michigan, Ann Arbor, MI
ABSTRACT- Progress in spatial ecology in general and metapopulation ecology in particular has been hindered by a lack of empirical tests of theory. This is primarily due to the logistical difficulties of conducting rigorous empirical work at large spatial scales. My research has addressed several predictions of metapopulation theory in a natural microcosm from the rainforests of eastern Madagascar. This system involves screw pines (Pandanus) and their obligate frog commensals, Mantidactylus bicalcaratus and M. punctatus. These frogs complete their entire life cycle in the water-filled leaf axils of Pandanus plants and, in this sense, Pandanus can been seen as relatively independent subpopulations in a larger metapopulation. Monitoring data from three years (2000-2002) in over 300 patches indicate relatively high and variable annual turnover rates (mean both species = 26%). However, dispersal patterns greatly influence these turnover rates and those patches that receive immigrants are less likely to turnover than those that did not receive immigrants (p = 0.04). This rescue effect is obvious for M. bicalcaratus but interpatch movements are much less common for M. punctatus. Differences in dispersal ability may permit the coexistence of these species in a shared patch network through the fugitive mechanism. In addition, the small spatial scale of this system has allowed an experimental approach. Experimental defaunation of patches resulted in an 80% recolonization rate for M. bicalcaratus and a 66% recolonization rate for M. punctatus over a 30 d period. The first patches to be recolonized after removing the resident frogs were those located close to source populations. Those patches not recolonized were the most spatially isolated. These results highlight the advantages of working in appropriate model systems that may serve as analogs of systems at larger spatial scales, where empirical work is more difficult.
KEY WORDS: metapopulations, rescue effect, frogs, Madagascar