Variations in the trophic ecology and densities of Ascaphus truei in two streams with different timber management histories

I examined the feeding ecology of tailed frogs (Ascaphus truer) and identified ways in whichthe populations and food resources of this riparian and old-growth associate varied between twostreams with different timber management histories. Data were collected during July and August1998 from two third order streams in the Willamette National Forest in western Oregon. MackCreek drains a pristine watershed in the H.J. Andrews Experimental Forest; Pasture Creek is west ofthe Sisters Wilderness Area, and the sampled reach is 3 km downstream from several small clear-cuts. Both sites historically supported Ascaphus truei. Feeding ecology was investigated by gutflushing and examining the gut contents of 45 frogs from Mack Creek. Population and range datafor individual tailed frogs were derived from mark-recapture studies on Mack and Pasture creeks.Tailed frog populations were larger in Mack Creek than in Pasture Creek with 39 ± 2 and 13 ± 1individuals respectively within comparable 50 m stream reaches. Individuals ranged over very shortreaches and exhibited high site fidelity in both streams. Average ranges were 4.0 ± 0.9 m of streamin Mack Creek and 2.5 ± 1.5 m in Pasture Creek. In-stream food sources accounted for 37% of themass of gut contents, whereas spiders and terrestrial insects accounted for 20% and 34%respectively. Dependence on the stream for food and apparent philopatry suggest that Ascaphus isvulnerable to natural and anthropogenic disturbances. Moreover, the lower epilithic biomass, algalbiomass, and aquatic invertebrate biomass in Pasture Creek suggests effects on Ascaphus foodresources resulting from the clear-cut. The higher water temperature and increased sedimentation inPasture Creek may also have affected the tailed frog population. Differences in water chemistrybetween watersheds was probably not a cause of the observed disparity in tailed frog populationsbetween Mack and Pasture creeks, but differences in temperature, sedimentation, and aquatic foodresources could be responsible.