Author: Corbin Cox KuntzePublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Habitat changes and prey depletion are among the most prominent drivers of near-global declines in predator populations. In particular, landscape homogenization - driven by climate change, anthropogenic land use, and management policies - can destabilize essential trophic interactions and represents a continuing threat to biodiversity and ecosystem function. Many predator and prey species occur, and likely evolved, in complex landscapes with heterogeneously distributed resources that shape many of their ecological interactions. A growing body of research has explored the role of spatial heterogeneity in predator-prey interactions, suggesting that heterogeneous landscapes containing prey refuges can decouple prey availability from abundance, with consequences when any one habitat type predominates. However, most of these studies are theoretical or lab-based, limited to controlled settings and by simplifying assumptions. Moreover, many studies of natural predator-prey systems are conducted at limited spatial scales, do not involve mobile predators, or fail to consider the role of alternative prey. As a result, our understanding of spatial heterogeneity - and the consequences of landscape simplification - remain limited by the available literature. This dissertation seeks to reduce key uncertainties and assess the emergent consequences of environmental change and landscape simplification on wildlife populations. Chapter 1 (Kuntze et al., 2024; Journal of Mammalogy) leveraged a 13-year monitoring dataset, stable isotope analysis, and high-resolution climate and habitat imagery to evaluate demographic responses of an isolated and endangered distinct population segment of fishers (Pekania pennanti) to rapid environmental change in the southern Sierra Nevada, California, USA. Fisher survival was sensitive to both biotic and abiotic factors, although the strength and direction of these effects were ultimately mediated by age and sex. These findings suggest that continued climate change will likely have consequences for Fishers through both incremental stressors and extreme weather events but increasing forest heterogeneity may help to buffer against the impacts of such change. Further, this study illustrates the importance of disentangling the effects of intrinsic and extrinsic factors on survival, especially among species with distinct sexual or ontogenetic differences.Chapter 2 (Kuntze et al., 2023; Ecological Applications) is the first of three that focuses on predator-prey dynamics between the spotted owl (Strix occidentalis) - an iconic old-forest species at the center of forest management planning in western North America - and one of its principal prey species, the dusky-footed woodrat (Neotoma fuscipes) - a younger forest species. This chapter explores the hypothesis that heterogeneous landscapes can create sources or spatial refuges for prey that ultimately benefit predator and prey populations when each are associated with different habitats. Here, we combined mark-recapture and survival monitoring of woodrats with direct observations of prey deliveries by spotted owls, and found that (1) woodrat abundance was higher within spotted owl home ranges defined by a heterogeneous mix of mature forest, young forest, and open areas, (2) woodrat mortality rates were low across all forest types (although all observed owl predation occurred within mature forests) and did not differ between heterogeneous and homogeneous owl home ranges, (3) owl consumption of woodrats increased linearly with woodrat abundance, and (4) consumption of alternative prey could not reconcile the deficit of reduced woodrat captures in homogeneous home ranges, as owls in heterogeneous landscapes delivered 30% more total prey biomass - equivalent to the energetic needs of producing one additional young. These findings represent some of the first empirical evidence from natural systems that promoting landscape heterogeneity can provide co-benefits to both predator and prey populations and constitute an effective strategy for conserving endangered predator populations. Chapter 3 (in review at Journal of Animal Ecology) contrasts foraging strategies within the context of a primary and secondary prey species to experimentally evaluate whether the magnitude of perceived risk, and in turn, the nature and strength of anti-predator investment, is governed by both predation intensity and the setting in which an encounter takes place. We studied the effects of spotted owls on two species experiencing asymmetrical predation pressures: dusky-footed woodrats (primary prey) and deer mice (Peromyscus spp., alternative prey). Woodrats exhibited behavioral responses to both background and acute risk at each stage of the foraging process, while deer mice only responded to acute risk. This suggests that prey may conform to or depart from the risk allocation hypothesis (i.e., that background risk modulates responses to immediate cues of predation risk) depending on relative predation risk from a shared predator. Furthermore, woodrats and deer mice employed time allocation and apprehension in different manners and under opposing circumstances, highlighting that primary and secondary prey can exhibit profound differences in both how risk is perceived, as well as how it is managed. Finally, Chapter 4 (prepared for Forest Ecology and Management) characterizes patterns in woodrat site occupancy at site-, patch-, and landscape-scales within landscapes where forest heterogeneity was created by even-aged timber management. Woodrats were more likely to occupy sites with greater canopy cover, understory cover, and hardwoods - particularly tanoak (Notholithocarpus densiflorus) - and smaller patches of young forest. Woodrats were also more likely to occur in mature forests in close proximity to younger forest, suggesting that high-quality habitat patches can produce dense populations that recruit into adjacent, lower-quality patches. These findings highlight the benefit of multiscale studies and provide insight into management activities that may benefit species conservation without compromising resilience in forest ecosystems. These latter three chapters collectively demonstrate that heterogeneity in vegetation types including high-density young forests increased the abundance and availability of early-successional woodrats that, in turn, provided energetic and potentially reproductive benefits to mature forest-associated spotted owls. Overall, this dissertation provides empirical support for theoretical studies on the role of heterogeneity (and the mechanisms conferring co-benefits), as well as contingencies mediating anti-predator behaviors, fit to the appropriate spatial scales.