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Effects of urbanization on arthropod diversity, community structure and trophic dynamics

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Urban ecosystems cover less than 3% of the Earth's land surface, yet more than half of the human population lives in urban areas. The process of urbanization stresses biodiversity and other ecosystem functions within and far beyond the city. To understand the mechanisms underlying observed changes in biodiversity patterns, several…

Urban ecosystems cover less than 3% of the Earth's land surface, yet more than half of the human population lives in urban areas. The process of urbanization stresses biodiversity and other ecosystem functions within and far beyond the city. To understand the mechanisms underlying observed changes in biodiversity patterns, several observational and experimental studies were performed in the metropolitan area of Phoenix, Arizona, and the surrounding Sonoran Desert. The first study was comprised of seven years of arthropod monitoring using pitfall traps in common urban land-use types. This study revealed differences in community structure, diversity and abundance over time and between urban and wildland habitats. Urban habitats with high productivity had higher abundances of arthropods, but lower diversity compared to wildland habitats. Arthropod abundance in less-productive urban habitats was positively correlated with precipitation, but abundance in high-productivity urban habitats was completely decoupled from annual fluctuations in precipitation. This study showed the buffering capacity and the habitat heterogeneity of urban areas. To test the mechanisms controlling community diversity and structure in urban areas, a major field experiment was initiated. Productivity of the native shrub Encelia farinosa and bird predation of associated arthropods were manipulated to test whether bottom-up or top-down forces were more important in urban habitats compared to wildland habitats. Abundance, richness and similarity were monitored, revealing clear differences between urban and wildland habitats. An unusually cold and dry first season had a negative effect on plant growth and arthropod abundance. Plants in urban habitats were relatively unaffected by the low temperature. An increase in arthropod abundance with water availability indicated bottom-up forces in wildland habitats, whereas results from bird exclusions suggested that bird predation may not be as prominent in cities as previously thought. In contrast to the pitfall study, arthropod abundance was lower in urban habitats. A second field experiment testing the sheltering effect of urban structures demonstrated that reduced wind speed is an important factor facilitating plant growth in urban areas. A mathematical model incorporating wind, water and temperature demonstrated that urban habitats may be more robust than wildland habitats, supporting the empirical results.
ContributorsBang, Christofer (Author) / Faeth, Stanley H. (Thesis advisor) / Sabo, John L. (Thesis advisor) / Grimm, Nancy (Committee member) / Anderies, J. Marty (Committee member) / Warren, Paige S. (Committee member) / Arizona State University (Publisher)
Created2010
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Diet Selection by Bobcats (Lynx rufus) and Coyotes (Canis latrans) Relative to Prey Availability and Urbanization in Space and Time

Description
Understanding the drivers of diet selection by carnivores is key for wildlife conservation and management, particularly in the Anthropocene. Yet, most assessments of predation do not consider how spatio-temporal prey availability or nutrition influence carnivore diet selection. Using a novel data integration approach for camera trap and scat data, I…

Understanding the drivers of diet selection by carnivores is key for wildlife conservation and management, particularly in the Anthropocene. Yet, most assessments of predation do not consider how spatio-temporal prey availability or nutrition influence carnivore diet selection. Using a novel data integration approach for camera trap and scat data, I assessed how spatial and temporal components of prey availability influenced diet selection by bobcats (Lynx rufus) in Colorado, USA (Chapter 1) and coyotes (Canis latrans) in Arizona, USA (Chapter 2) in areas of low and moderate levels of urbanization. I also assessed coyote diets using the nutritional geometric framework to determine coyote macronutrient consumption seasonally and relative to urbanization (Chapter 3). My results suggest that cottontail rabbit availability largely drove bobcat predation, and that bobcats consumed prey relative to its availability overall and in wildland areas, but that this relationship weakened in anthropogenic regions. I also found that, overall, models of prey availability that incorporated the temporal overlap between predator and prey taxa predicted bobcat diet selection better than models assessing the spatial availability of prey. Similarly, I found coyotes consumed prey relative to its availability overall and in sites with lower levels of human influence across seasons, but not in moderately urbanized sites. I also found that models of prey availability that incorporated time better predicted coyote diets compared to models assessing the spatial availability of prey. Finally, I observed that the macronutrient composition of coyote diets was similar between moderately and less urbanized sites, particularly in the spring-summer season. However, coyote macronutrient consumption differed seasonally, with coyotes eating more non-protein energy relative to protein energy when carbohydrate-rich mesquite (Prosopis spp.) was more available in the fall-winter. In addition, the consistently high consumption of lipid-rich domestic cats in moderately urbanized sites further supports the hypothesis that coyotes increased their consumption of non-protein energy when available and when assuming protein needs were already met. This dissertation provides new insights into how urbanized landscapes impact carnivore ecology. Since diet selection drives many human-carnivore conflicts, this research can also be used to help inform wildlife management and decision-making in anthropogenic areas.
ContributorsWeiss, Katherine (Author) / Sterner, Beckett (Thesis advisor) / Schipper, Jan (Thesis advisor) / Deviche, Pierre (Committee member) / Lewis, Jesse S (Committee member) / Strauss, Eric G (Committee member) / Arizona State University (Publisher)
Created2024
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Personality in the City: Relationship Between Animal Behavioral Traits And Urbanization in a Fragile, Human-impacted Desert Ecosystem

Description
Human-inhabited or -disturbed areas pose many unique challenges for wildlife, including increased human exposure, novel challenges, such as finding food or nesting sites in novel structures, anthropogenic noises, and novel predators. Animals inhabiting these environments must adapt to such changes by learning to exploit new resources and avoid danger. To…

Human-inhabited or -disturbed areas pose many unique challenges for wildlife, including increased human exposure, novel challenges, such as finding food or nesting sites in novel structures, anthropogenic noises, and novel predators. Animals inhabiting these environments must adapt to such changes by learning to exploit new resources and avoid danger. To my knowledge no study has comprehensively assessed behavioral reactions of urban and rural populations to numerous novel environmental stimuli. I tested behavioral responses of urban, suburban, and rural house finches (Haemorhous mexicanus) to novel stimuli (e.g. objects, noises, food), to presentation of a native predator model (Accipiter striatus) and a human, and to two problem-solving challenges (escaping confinement and food-finding). Although I found few population-level differences in behavioral responses to novel objects, environment, and food, I found compelling differences in how finches from different sites responded to novel noise. When played a novel sound (whale call or ship horn), urban and suburban house finches approached their food source more quickly and spent more time on it than rural birds, and urban and suburban birds were more active during the whale-noise presentation. In addition, while there were no differences in response to the native predator, rural birds showed higher levels of stress behaviors when presented with a human. When I replicated this study in juveniles, I found that exposure to humans during development more accurately predicted behavioral differences than capture site. Finally, I found that urban birds were better at solving an escape problem, whereas rural birds were better at solving a food-finding challenge. These results indicate that not all anthropogenic changes affect animal populations equally and that determining the aversive natural-history conditions and challenges of taxa may help urban ecologists better understand the direction and degree to which animals respond to human-induced rapid environmental alterations.
ContributorsWeaver, Melinda (Author) / McGraw, Kevin J. (Thesis advisor) / Rutowski, Ronald (Committee member) / Pratt, Stephen (Committee member) / Bateman, Heather (Committee member) / Deviche, Pierre (Committee member) / Arizona State University (Publisher)
Created2018
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Investigating the influence of food on reproductive physiology and gonad growth: urbanization as a natural experiment

Description
For animals that experience annual cycles of gonad development, the seasonal timing (phenology) of gonad growth is a major adaptation to local environmental conditions. To optimally time seasonal gonad growth, animals use environmental cues that forecast future conditions. The availability of food is one such environmental cue. Although the importance…

For animals that experience annual cycles of gonad development, the seasonal timing (phenology) of gonad growth is a major adaptation to local environmental conditions. To optimally time seasonal gonad growth, animals use environmental cues that forecast future conditions. The availability of food is one such environmental cue. Although the importance of food availability has been appreciated for decades, the physiological mechanisms underlying the modulation of seasonal gonad growth by this environmental factor remain poorly understood.

Urbanization is characterized by profound environmental changes, and urban animals must adjust to an environment vastly different from that of their non-urban conspecifics. Evidence suggests that birds adjust to urban areas by advancing the timing of seasonal breeding and gonad development, compared to their non-urban conspecifics. A leading hypothesis to account for this phenomenon is that food availability is elevated in urban areas, which improves the energetic status of urban birds and enables them to initiate gonad development earlier than their non-urban conspecifics. However, this hypothesis remains largely untested.

My dissertation dovetailed comparative studies and experimental approaches conducted in field and captive settings to examine the physiological mechanisms by which food availability modulates gonad growth and to investigate whether elevated food availability in urban areas advances the phenology of gonad growth in urban birds. My captive study demonstrated that energetic status modulates reproductive hormone secretion, but not gonad growth. By contrast, free-ranging urban and non-urban birds did not differ in energetic status or plasma levels of reproductive hormones either in years in which urban birds had advanced phenology of gonad growth or in a year that had no habitat-related disparity in seasonal gonad growth. Therefore, my dissertation provides no support for the hypothesis that urban birds begin seasonal gonad growth because they are in better energetic status and increase the secretion of reproductive hormones earlier than non-urban birds. My studies do suggest, however, that the phenology of key food items and the endocrine responsiveness of the reproductive system may contribute to habitat-related disparities in the phenology of gonad growth.
ContributorsDavies, Scott (Author) / Deviche, Pierre (Thesis advisor) / Sweazea, Karen (Committee member) / McGraw, Kevin (Committee member) / Orchinik, Miles (Committee member) / Warren, Paige (Committee member) / Arizona State University (Publisher)
Created2014