| The distribution of freshwater is a key determinant of terrestrial life on earth. While physiological ecologists and plant biologists have long recognized the fundamental role of water in influencing the biology of organisms, populations, and communities, animal community ecologists have largely ignored the direct importance of this resource, focusing more on energy or nutrients, like nitrogen. A key challenge facing ecologists is to predict the impacts of environmental change on populations, communities and ecosystems, a challenge which has become more pressing in light of recent climate change and growth in the human modification and use of freshwater resources In this dissertation, I examine how terrestrial animal communities are influenced by changes in water resources, using a water web approach, where water is considered the currency connecting terrestrial organisms First, I develop a new method of using stable water isotopes of O and H to trace sources of water used by terrestrial animals. Second, I show that in dry environments, water controls rates of resource consumption at two trophic levels, with effects on interaction strength between predators and prey. Third, I show that river drying events along the San Pedro River in southeastern AZ correspond with decreased taxonomic diversity and altered community composition of ground-dwelling riparian arthropods, contrary to common assumptions that desert riparian species are adapted to river drying events. I also find that changes in the riparian arthropod community along this drying river seem most associated with changes in water availability measures. Finally, I show that changes in terrestrial riparian arthropods observed with river drying can be partially decreased by the addition of artificial pools along a drying river, displaying a causal relationship between previously observed patterns. Overall, my results show the strong influence of variation in water availability on terrestrial animal communities, highlighting the importance of considering this resource in studies of ecological response to global change. |
