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METAPOPULATION PROCESSES OF INFINITE DISPERSAL?: HABITAT PATCH OCCUPANCY BY TOADS (BUFO PUNCTATUS) IN A NATURALLY FRAGMENTED DESERT
Citation:
Bradford, D F., A C. Neale, M S. Nash, D. W. Sada, AND J R. Jaeger. METAPOPULATION PROCESSES OF INFINITE DISPERSAL?: HABITAT PATCH OCCUPANCY BY TOADS (BUFO PUNCTATUS) IN A NATURALLY FRAGMENTED DESERT. Presented at Annual Meeting of Desert Fishes Council, Death Valley National Park, NV, November 22-23, 2003.
Description:
Amphibians are often thought to have a metapopulation structure, which may render them vulnerable to habitat fragmentation. The red-spotted toad (Bufo punctatus) in the southwestern USA and Mexico commonly inhabits wetlands that have become much smaller and fewer since the late Pleistocene. This study tests two predictions based on metapopulation theory '--- the incidence of habitat patch occupancy is directly related to patch size and inversely related to patch isolation ---and a third, potentially competing hypothesis that patch occupancy is influenced by local environmental conditions. In a 20,000 km2 area of the eastern Mojave
Desert, 128 potential habitat patches (primarily springs) were identified and surveyed for local environmental characteristics and presence/absence of B. punctatus. Patch isolation metrics were based on nearest-neighbor distances, calculated both as Euclidian distance and distance via connecting drainage channels. B. punctatus was found at 73% of the sites, including all of the 15 historic (pre-1970) sites. Based on stepwise multiple logistic regression, the incidence of patch occupancy increased significantly with patch size, and was also significantly related to elevation, latitude, and four metrics that were associated with rocky terrain, periodic scouring water flows, and ephemeral water. In contrast, incidence of patch occupancy was not significantly related to patch isolation. These findings are consistent with a "patchy population" model, rather than the classical equilibrium metapopulation model, implying frequent dispersal among patches and virtually no local extinctions. Implicated dispersal distances of many kilometers are large for an amphibian.