Multiscale Habitat Relationships of Stream Amphibians in the Klamath-Siskiyou Region of California and Oregon

Abstract

Regional amphibian distribution patterns can vary greatly depending on species and the spatial scale of inquiry (e.g., landscape to microenvironment). These differences appear to be related both to habitat selection among species as well as availability of suitable habitats across scales. We sampled amphibians in 39 second- and third-order streams in the conifer-hardwood forests of northwestern California and southwestern Oregon, USA (the Klamath-Siskiyou Region) during 1984 and 1985. We concurrently measured spatial, structural, compositional, and climatic attributes of the forest and stream environment-attributes representing landscape, macroenvironment, and microenvironment scales-to determine key habitat relationships. We captured 7 species, 97% of which were larval and paedomorphic Pacific giant salamanders (Dicamptodon tenebrosus) and larval and adult tailed frogs (Ascaphus truei). Streams in late seral forests supported both the highest diversity of amphibians and the highest densities of A. truei. Overall, A. truei distribution was patchy in occurrence, while D. tenebrosus distribution was widespread throughout the region at all scales. The incidence of A. truei was assessable at the landscape, macroenvironment, and microenvironment scales; however, variation in density was most predictable at the microenvironment scale. Changes in density of D. tenebrosus were detected only at the microenvironment scale. Tree size class and plant species composition variables distinguishing younger from older, more structurally complex forests, and forest microclimates and in-stream attributes best determined the presence and density for both life stages of A. truei. However, only in-stream conditions were good predictors of D. tenebrosus density. A. truei occupied a narrower range of habitat conditions than D. tenebrosus, exhibiting an ecological dependence on lotic and riparian environments found more reliably in late serai forests.