Graduate Thesis Or Dissertation
 

Patterns in responses of an amphibian assemblage to wetland restoration

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/4j03d3192

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  • Wetland restoration success in attaining wildlife conservation goals can be confounded by the presence of multiple biological invaders. Wetland management activities typically target invasive plants, but bottom-up responses of higher trophic levels in novel communities are difficult to predict. We surveyed plant and amphibian assemblages at 26 sites enrolled in the Wetlands Reserve Program (WRP) in the Willamette Valley, Oregon to determine the relative importance of plant management, non-native species presence, and surrounding landscape for amphibians across multiple life history stages. Explanatory variables negatively associated with native anuran counts included percent invasive plant cover, invasive bullfrog counts, non-native fish presence, and area of urban land cover. In addition, native anurans were positively associated with WRP site age, suggesting that the benefits of restored wetlands may increase over time. Although invasive plant management provided indirect benefits to native amphibians, the most effective way to enhance native amphibian populations may be through eliminating the strong top-down forces exerted by non-native vertebrates. We also explored the impact of restoration activities on predator/prey dynamics by analyzing bullfrog diet contents. We sampled vegetation and analyzed bullfrog diet contents from 10 WRP wetlands categorized by management intensity and hydrology to determine whether prey consumption patterns (abundance, richness, and % large prey), diet breadth, and dietary community (based on taxonomic and prey size composition) differed among wetlands categorized by management regime and hydroperiod. We found disparities in the diet breadth with respect to wetland categories, with bullfrogs consuming a disproportionate abundance of few prey orders at actively managed sites. Diet breadth could have been influenced by frequent applications of restoration treatments, as invertebrate species richness and abundance is often negatively linked to habitat disturbance. Dietary taxonomic composition also differed between wetland groups, but prey size composition did not. Instead, prey size was strongly influenced by site-level vegetation covariates; large-bodied prey consumption was positively associated with plant species richness. However, diet dry mass was highest in wetlands with high invasive plant cover, suggesting that other factors, such as foraging activity rates, should be considered to fully understand how bullfrogs meet energy demands in managed wetlands. Variation in native and invasive amphibian responses to wetland restoration efforts may provide important information on how habitat structure and composition influence trophic dynamics. Given that the outcomes of plant control on wildlife may not follow planned trajectories in invasive-dominated systems, this research addresses the need for a community approach to assessments of restoration success.
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