Relative Effects of Landscape Structure Variables, and Interactions with Life-History Traits, on the Abundance and Distribution of Wetland-Dependent Vertebrate Species

Wetland-dependent species are undergoing the largest wildlife population declines worldwide primarily due to habitat loss, but are a relatively understudied ecological group in landscape ecology. The overarching goal of my dissertation is to advance our understanding of the effects of landscape structure on wetland-dependent vertebrate populations and the life-history traits that determine these responses. In Chapter 2, I used meta-analysis to combine data on the relationship between species abundance and wetland habitat loss from empirical studies conducted worldwide to identify the traits that influence species response to habitat loss. I show that species with low reproductive rates are more sensitive to habitat loss at the population level, whereas species mobility has no apparent effect. In Chapter 3, I conducted extensive field surveys to determine the relative effects of landscape structure variables on the distribution of wetland birds and turtles. I show that birds are more strongly affected by habitat loss whereas turtles are more strongly affected by the surrounding landscape matrix, specifically forest cover. I also show that habitat fragmentation independent of habitat loss was not an important predictor for any species. In Chapter 4, I investigated whether a similar pattern is found in other studies and vertebrate taxa by building upon the meta-analysis in Chapter 2 and comparing wetland species responses to wetland loss and landscape matrix quality at the population level. I show that wetland loss is more important for mammals and birds whereas matrix quality, indexed as forest cover, is more important for amphibians. I also show that these results are not scale-dependent. The results of this thesis suggest that conservation priority should be placed on species with low reproductive rates and on actions that increase reproductive output rather than movement. My results also suggest that landscape-scale requirements vary among wetland-dependent taxa: mammals and birds are more limited by the amount of wetland habitat in a landscape, whereas amphibians and reptiles are more limited by the quality of the matrix surrounding wetlands, likely due to access to and/or availability of complementary habitats. Therefore, conservation policies that focus only on wetland protection will not conserve wetland biodiversity.