Matching Items (3)
Filtering by

Clear all filters

149374-Thumbnail Image.png
Description

River and riparian areas are important foraging habitat for insectivorous bats. Numerous studies have shown that aquatic insects provide an important trophic resource to terrestrial consumers, including bats, and are key in regulating population size and species interactions in terrestrial food webs. Yet these studies have generally ignored how structural

River and riparian areas are important foraging habitat for insectivorous bats. Numerous studies have shown that aquatic insects provide an important trophic resource to terrestrial consumers, including bats, and are key in regulating population size and species interactions in terrestrial food webs. Yet these studies have generally ignored how structural characteristics of the riverine landscape influence trophic resource availability or how terrestrial consumers respond to ensuing spatial and temporal patterns of trophic resources. Moreover, few studies have examined linkages between a stream's hydrologic regime and the timing and magnitude of aquatic insect availability. The main objective of my dissertation is to understand the causes of bat distributions in space and time. Specifically, I examine how trophic resource availability, structural components of riverine landscapes (channel confinement and riparian vegetation structure), and hydrologic regimes (flow permanence and timing of floods) mediate spatial and temporal patterns in bat activity. First, I show that river channel confinement determines bat activity along a river's longitudinal axis (directly above the river), while trophic resources appear to have stronger effects across a river's lateral (with distance from the river) axis. Second, I show that flow intermittency affects bat foraging activity indirectly via its effects on trophic resource availability. Seasonal river drying appears to have complex effects on bat foraging activity, initially causing imperfect tracking by consumers of localized concentrations of resources but later resulting in disappearance of both insects and bats after complete river drying. Third, I show that resource tracking by bats varies among streams with contrasting patterns of trophic resource availability and this variation appears to be in response to differences in the timing of aquatic insect emergence, duration and magnitude of emergence, and adult body size of emergent aquatic insects. Finally, I show that aquatic insects directly influence bat activity along a desert stream and that riparian vegetation composition affects bat activity, but only indirectly, via effects on aquatic insect availability. Overall, my results show river channel confinement, riparian vegetation structure, flow permanence, and the timing of floods influence spatial and temporal patterns in bat distributions; but these effects are indirect by influencing the ability of bats to track trophic resources in space and time.

ContributorsHagen, Elizabeth M (Author) / Sabo, John L (Thesis advisor) / Fisher, Stuart G. (Committee member) / Grimm, Nancy (Committee member) / Schmeeckle, Mark W (Committee member) / Stromberg, Juliet C. (Committee member) / Arizona State University (Publisher)
Created2010
161831-Thumbnail Image.png
Description
Globally, rivers are being heavily dammed and over-utilized to the point where water shortages are starting to occur. This problem is magnified in arid and semi-arid regions where climate change, growing populations, intensive agriculture and urbanization have created tremendous pressures on existing river systems. Regulatory incentives have been enacted in

Globally, rivers are being heavily dammed and over-utilized to the point where water shortages are starting to occur. This problem is magnified in arid and semi-arid regions where climate change, growing populations, intensive agriculture and urbanization have created tremendous pressures on existing river systems. Regulatory incentives have been enacted in recent decades that have spurred river restoration programs in the United States. But what kind of governance does river restoration require that is different from allocative institutional set-ups? Are these recovery programs succeeding in restoring ecological health and resilience of the rivers? Do the programs contribute to social-ecological resilience of the river systems more broadly? This study aims to tackle these key questions for two Colorado River sub-basin recovery programs (one in the Upper Basin and one in the Lower Basin) through utilization of different frameworks and methodologies for each. Organizational resilience to institutional and biophysical disturbances varies, with the Upper Basin program being more resilient than the Lower Basin program. Ecological resilience as measured by beta diversity (for the Upper Basin) was a factor of the level of hydrological and technological interventions rather than an occurrence of the natural flow regime. This points to the fact that in a highly-dampened and managed system like the Colorado River, the dampened flow regime alone is not a significant factor in maintaining community diversity and ecological health. A broad-scale social-ecological analysis supports the finding that the natural feedback between social and ecological elements is broken and recovery efforts are more an attempt at resuscitating the river system to maintain a semblance of historic levels of fish populations and aquatic processes. Adaptive management pathways for the future need to address and build pathways to transformability into recovery planning to achieve resilience for the river system.
ContributorsSrinivasan, Jaishri (Author) / Schoon, Michael L (Thesis advisor) / Sabo, John L (Thesis advisor) / White, Dave D (Committee member) / Janssen, Marcus A (Committee member) / Arizona State University (Publisher)
Created2021
171751-Thumbnail Image.png
Description
Primary producers, from algae to trees, play a pivotal role in community structure and ecosystem function. Primary producers vary broadly in their functional traits (i.e., morphological, physiological, biochemical, and behavioral characteristics), which determine how they respond to stimuli and affect ecosystem properties. Functional traits provide a mechanistic link between

Primary producers, from algae to trees, play a pivotal role in community structure and ecosystem function. Primary producers vary broadly in their functional traits (i.e., morphological, physiological, biochemical, and behavioral characteristics), which determine how they respond to stimuli and affect ecosystem properties. Functional traits provide a mechanistic link between environmental conditions, community structure, and ecosystem function. With climate change altering environmental conditions, understanding this mechanistic link is essential for predicting future community structure and ecosystem function. Competitive interactions and trait values in primary producers are often context dependent, whereby changes in environmental conditions and resources alter relationships between species and ecosystem processes. Well-established paradigms concerning how species in a community respond to each other and to environmental conditions may need to be re-evaluated in light of these environmental changes, particularly in highly variable systems. In this dissertation, I examine the role of primary producer functional traits on community structure and ecosystem function. Specifically, I test a conceptual framework that incorporates response traits, effect traits, and their interaction, in affecting primary producer communities and ecosystem function across different aquatic systems. First, I identified species-specific responses to intensifying hydrologic stressors important in controlling wetland plant community composition over time in an aridland stream. Second, I found that effect traits of submerged and emergent vegetation explained differences in ecosystem metabolism and carbon dynamics among permafrost mire thaw ponds. Next, I examined response-effect trait interactions by comparing two dominant wetland plant species over a water-stress gradient, finding that responses to changes in hydrology (i.e., altered tissue chemistry) in turn affect ecosystem processes (i.e., subsurface CO2 concentration). Finally, I demonstrate how indirect effects of diatom functional traits on water chemistry and ecosystem metabolism help explain disconnects between resource availability and productivity in the Colorado River. By expanding my understanding of how metabolic processes and carbon cycling in aquatic ecosystems vary across gradients in hydrology, vegetation, and organic matter, I contributed to my understanding of how communities influence ecosystem processes. A response-effect trait approach to understanding communities and ecosystems undergoing change may aid in predicting and mitigating the repercussions of future climate change.
ContributorsLauck, Marina Diane (Author) / Grimm, Nancy B (Thesis advisor) / Appling, Alison P (Committee member) / Childers, Dan E (Committee member) / Sabo, John L (Committee member) / Arizona State University (Publisher)
Created2022