Author: Courtney Lynn DavisPublisher:
ISBN:
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Languages : en
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Book Description
The effects of environmental change on individual species depend on interactions between climate, other co-occurring species, and the physical environment in which interactions occur. Despite this, commonly used methods for predicting species' responses to environmental change, such as bioclimatic envelope models, do not consider community dynamics or complex interactions between climate and the physical environment, making it difficult to predict how species distributions and community assemblages will be affected. The work presented in this dissertation uses novel or recently developed hierarchical modeling approaches to make inference about the dynamic processes structuring populations and communities, with a specific focus on understanding: 1) how species interact with one another across the landscape; 2) how species interact with their environment; and 3) how climate influences these interactions. In my first chapter, I analyzed camera trap data for 108,087 trap days across 12 countries spanning 5 continents to better understand how mammalian carnivore communities are structured globally. I used a two-species occupancy modeling approach to estimate local probabilities of co-occurrence among 768 species pairs from the order Carnivora and evaluate how shared ecological traits (e.g., activity pattern, diet, body size) correlate with probabilities of co-occurrence. I found that species pairs co-occurred more frequently than expected at random within individual study areas. Co-occurrence probabilities were greatest for species pairs that shared ecological traits including similar body size, temporal activity pattern, and diet. This indicates that shared habitat affinities are likely more important than niche separation in structuring carnivore communities. However, co-occurrence decreased as compared to other species pairs when the pair included a large-bodied carnivore. These results suggest that a combination of shared traits and top-down regulation by large carnivores shape local carnivore communities. This chapter represents the first global assessment of carnivore spatial co-occurrence patterns and provides a framework for other collaborative, global-scale studies on interactions among species. The novelty of my study comes in the ability to assess how these important communities are organized across the globe. Global monitoring efforts and analyses such as these are vital to understanding the underlying processes of community structure and assembly, as well as the conservation of wildlife populations at local, regional, and global scales. In my second chapter, I used data from a 6-year capture-mark-recapture study (2014 to 2019) of adult spotted salamanders (Ambystoma maculatum) in central Pennsylvania, USA, to estimate population connectivity among breeding wetlands. I quantified inter- and intra-annual site fidelity, breeding dispersal probabilities as a function of distance between wetlands, abundance, and annual survival using a multistate, hidden Markov estimator. I found that inter-annual site fidelity of males varied among wetlands and was positively associated with population density. Females exhibited higher inter-annual site fidelity and dispersed further than males between breeding seasons. Within breeding seasons, I found that up to 6% of males dispersed to a new wetland each day. These results indicate high population connectivity and suggest that long-term population persistence in this study system will depend on maintaining wetlands that vary in size, hydroperiod and spatial proximity. This chapter represents the first study to directly compare amphibian breeding dispersal probabilities and distances at multiple scales, and provides a robust framework for improving inference on the spatial and temporal patterns of amphibian movement. Lastly, in my third chapter, I used multi-species occupancy and structural equation modeling approaches to quantify the direct and indirect effects of extreme weather events on a coastal freshwater wetland system. I used data from an 8-year study (2009 to 2016) on St. Marks National Wildlife Refuge in Florida, USA, to quantify species-specific and community-level changes in amphibian and fish occupancy associated with extreme flooding events in 2012 and 2013. Specifically, I examined how physical changes to the landscape, including changes in salinity and increased wetland connectivity, may have contributed to or exacerbated the effects of these extreme weather events on the biota of isolated coastal wetlands. I was able to demonstrate that the indirect effects of flooding on amphibians, via changes in the composition of the fish community and salinity, were species-specific and driven, at least in part, by life history traits (e.g., breeding strategy). These extreme weather events led to an overall decline in local amphibian species richness observed from 2009 to 2016, suggesting that coastal wetland-breeding communities on St. Marks may not be resilient to the predicted changes in disturbance regimes as a result of climate change. In combination with long-term monitoring data, the integrated framework I developed in this chapter allows for more robust predictions regarding the ecosystem-level impacts of a changing climate. With recent efforts to coordinate, consolidate and integrate ecological data from various ecosystems across large temporal and spatial scales, there is a huge demand for efficient yet effective statistical tools. Each of the three chapters described above use a different hierarchical modeling approach to make inference about the processes structuring populations and communities, while accounting observational uncertainty. The work presented in this dissertation further develops the utility and accessibility of these methods, such that other ecologists can use these tools to better understand population- and community-level responses to variable environments and changing conditions.