In the Willamette Valley, Oregon, the invasive American bullfrog and a variety of non-native sport fish are implicated in declines of native amphibians. Few long-term community studies of invasive-native interactions exist, and such studies are often complicated by confounding habitat modifications.
USGS and Oregon State University scientists assessed the influence of invasive species and habitat on the distributions of five native amphibian species using a multispecies dynamic occupancy model accounting for both false-negative and false-positive species detections. They found habitat characteristics, such as within-pond vegetation cover, surrounding forest, and drought severity, were important for local persistence of native species when bullfrogs co-occurred. Non-native fish and bullfrogs did not appear to be drivers of native amphibian declines, however, both invaders together had a cumulative negative effect on red-legged frog (Rana aurora) persistence. Invasive species management often focuses on population-level control of invaders, which can be costly and impractical. This research suggests habitat may play the strongest role in regulating native amphibian persistence in this system, allowing natives to coexist with invaders under favorable habitat conditions.
Rowe, J.C., Duarte, A., Pearl, C.A., McCreary, B., Galvan, S.K., Peterson, J.T., Adams, M.J., 2019, Disentangling effects of invasive species and habitat while accounting for observer error in a long-term amphibian study: Ecosphere, v. 10, no. 4, p. e02674, https://doi.org/10.1002/ecs2.2674