Graduate Thesis Or Dissertation
 

Habitat structure and occupancy patterns of the montane frog, Rana cascadae, in the Cascade Range, Oregon, at multiple scales : implications for population dynamics in patchy landscapes

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3484zn022

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  • Associations between occupancy patterns of a montane anuran species, Rana cascadae, and habitat structure at multiple scales were examined to investigate how population structure may influence persistence in spatially and temporally heterogeneous environments. Predictions were based on population dynamics suggested by source-sink and metapopulation models. Potential sites in three basins in the central Cascade Range, Oregon, were identified from aerial photos, fieldverified, and surveyed for eggs, tadpoles, and adults. Habitat quality at each site (i.e. vegetation, shoreline topography, area, water retention) and connectivity among sites (i.e. distance, gradient, connecting creeks) were measured to investigate factors that may be associated with distribution patterns at local and regional scales. Habitat structure at the site scale explained many of R. cascadae occupancy patterns. Breeding sites generally were small vegetated ponds with gradual shoreline topography, or flooded meadows. Adults, juveniles, and metamorphs were found in a wider variety of sites including small vegetated ponds, larger deeper lakes, meadows, and creeks. A strong association was found between occupancy and water retention. A large proportion of sites that retained water through the summer were occupied by at least one life history stage. Connectivity metrics were not associated with the distribution of breeding sites; breeding sites generally were dispersed when measured by all metrics. However, the occupancy patterns of adults suggested that frogs moved among sites. In McKenzie Pass, the high density of sites may provide stepping stones, whereas in Three Creeks and Todd Lake, the flowing creeks may provide corridors. Rana cascadae appears to be well adapted to living in a spatially and temporally heterogeneous environment. Breeding was associated with habitat characteristics that may favor rapid development. Habitat and adult occupancy associations suggested that the frog's home range may be larger than a single site. Given the unpredictable environment, use of other habitats such as creeks and large lakes may enable frogs to survive stressful periods. The apparent high mobility may facilitate access to potentially critical alternate habitat, immigration that may "rescue" extant populations, and recolonization of sites where populations have gone extinct. Conservation plans should protect the range of habitats required at multiple spatial scales.
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