Matching Items (6)

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Soil moisture availability and energetic controls on belowground network complexity and function in arid ecosystems

Description

The explicit role of soil organisms in shaping soil health, rates of pedogenesis, and resistance to erosion has only just recently begun to be explored in the last century. However,

The explicit role of soil organisms in shaping soil health, rates of pedogenesis, and resistance to erosion has only just recently begun to be explored in the last century. However, much of the research regarding soil biota and soil processes is centered on maintaining soil fertility (e.g., plant nutrient availability) and soil structure in mesic- and agro- ecosystems. Despite the empirical and theoretical strides made in soil ecology over the last few decades, questions regarding ecosystem function and soil processes remain, especially for arid areas. Arid areas have unique ecosystem biogeochemistry, decomposition processes, and soil microbial responses to moisture inputs that deviate from predictions derived using data generated in more mesic systems. For example, current paradigm predicts that soil microbes will respond positively to increasing moisture inputs in a water-limited environment, yet data collected in arid regions are not congruent with this hypothesis. The influence of abiotic factors on litter decomposition rates (e.g., photodegradation), litter quality and availability, soil moisture pulse size, and resulting feedbacks on detrital food web structure must be explicitly considered for advancing our understanding of arid land ecology. However, empirical data coupling arid belowground food webs and ecosystem processes are lacking. My dissertation explores the resource controls (soil organic matter and soil moisture) on food web network structure, size, and presence/absence of expected belowground trophic groups across a variety of sites in Arizona.

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Agent

Created

Date Created
  • 2014

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Indirect Effects of Omnivorous Crayfish on Semiarid Stream Macroinvertebrate Communities Mediated by Novel Riparian Vegetation

Description

Novel resource inputs represent an increasingly common phenomenon in ecological systems as global change alters environmental factors and species distributions. In semiarid riparian areas, hydric pioneer tree species are being

Novel resource inputs represent an increasingly common phenomenon in ecological systems as global change alters environmental factors and species distributions. In semiarid riparian areas, hydric pioneer tree species are being replaced by drought-tolerant species as water availability decreases. Additionally, introduced omnivorous crayfish, which feed upon primary producers, allochthonous detritus, and benthic invertebrates, can impact communities at multiple levels through both direct and indirect effects. In arid and semiarid systems of the American Southwest, crayfish may be especially important as detrital processors due to the lack of specialized detritivores. I tested the impact of virile crayfish (Orconectes virilis) on benthic invertebrates and detrital resources across a gradient of riparian vegetation drought-tolerance using field cages with leaf litter bags in the San Pedro River in Southeastern Arizona. Virile crayfish increased breakdown rate of drought-tolerant saltcedar (Tamarix ramosissima), but did not impact breakdown of Fremont cottonwood (Populus fremontii), Gooding's willow (Salix goodingii), or seepwillow (Baccharis salicifolia). The density and composition of the invertebrate community colonizing leaf litter bags were both heavily influenced by litter species but not directly by crayfish presence. As drought-tolerant species become more abundant in riparian zones, their litter will become a larger component of the organic matter budget of desert streams. By increasing breakdown rates of saltcedar, crayfish shift the composition of leaf litter in streams, which in turn may affect the composition and biomass of colonizing invertebrate communities. More research is needed to determine the full extent to which these alterations change community composition over time.

Contributors

Agent

Created

Date Created
  • 2012

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The effects of non-native and native anuran tadpoles on aquatic ecosystem processes

Description

Non-native consumers can significantly alter processes at the population, community, and ecosystem level, and they are a major concern in many aquatic systems. Although the community-level effects of non-native anuran

Non-native consumers can significantly alter processes at the population, community, and ecosystem level, and they are a major concern in many aquatic systems. Although the community-level effects of non-native anuran tadpoles are well understood, their ecosystem-level effects have been less studied. Here, I tested the hypothesis that natural densities of non-native bullfrog tadpoles (Lithobates catesbeianus) and native Woodhouse's toad tadpoles (Anaxyrus woodhousii) have dissimilar effects on aquatic ecosystem processes because of differences in grazing and nutrient recycling (excretion and egestion). I measured bullfrog and Woodhouse's carbon, nitrogen, and phosphorus nutrient recycling rates. Then, I determined the impact of tadpole grazing on periphyton biomass (chlorophyll a) during a 39-day mesocosm experiment. Using the same experiment, I also quantified the effect of tadpole grazing and nutrient excretion on periphyton net primary production (NPP). Lastly I measured how dissolved and particulate nutrient concentrations and respiration rates changed in the presence of the two tadpole species. Per unit biomass, I found that bullfrog and Woodhouse's tadpoles excreted nitrogen and phosphorus at similar rates, though Woodhouse's tadpoles egested more carbon, nitrogen, and phosphorus. However, bullfrogs recycled nutrients at higher N:C and N:P ratios. Tadpole excretion did not cause a detectable change in dissolved nutrient concentrations. However, the percent phosphorus in mesocosm detritus was significantly higher in both tadpole treatments, compared to a tadpole-free control. Neither tadpole species decreased periphyton biomass through grazing, although bullfrog nutrient excretion increased areal NPP. This result was due to higher biomass, not higher biomass-specific productivity. Woodhouse's tadpoles significantly decreased respiration in the mesocosm detritus, while bullfrog tadpoles had no effect. This research highlights functional differences between species by showing non-native bullfrog tadpoles and native Woodhouse's tadpoles may have different effects on arid, aquatic ecosystems. Specifically, it indicates bullfrog introductions may alter primary productivity and particulate nutrient dynamics.

Contributors

Agent

Created

Date Created
  • 2015

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Spatial and temporal patterns in insectivorous bat activity in river-riparian landscapes

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

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.

Contributors

Agent

Created

Date Created
  • 2010

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Ecosystem Impacts of Consumer Evolution: Intraspecific Variation in the Elemental Phenotype of Aquatic Consumers

Description

Primary production in aquatic ecosystems is often limited by the availability of nitrogen (N) and/or phosphorus (P). Animals can substantially alter the relative availability of these nutrients by storing and

Primary production in aquatic ecosystems is often limited by the availability of nitrogen (N) and/or phosphorus (P). Animals can substantially alter the relative availability of these nutrients by storing and recycling them in differential ratios. Variation in these stoichiometric traits, i.e., the elemental phenotype, within a species can link organismal evolution to ecosystem function. I examined the drivers of intraspecific variation in the elemental phenotype of aquatic consumers to test for the generality of these effects. Over a thermal gradient in Panamá, I found that average specific growth grate and body P content of the mayfly Thraulodes increased with environmental temperature, but that these patterns were due to site-specific differences rather than the direct effects of warmer temperature. In a meta-analysis of published studies, I found that in fishes intraspecific variation in dietary N:P ratio had a significant effect on excretion N:P ratio, but only when accounting for consumption. I tested for the effects of variation in consumption on excretion N:P ratio among populations of the fish Gambusia marshi in the Cuatro Ciénegas basin in Coahuila, Mexico. G. marshi inhabits warm groundwater-fed springs where it often co-occurs with predatory fishes and cool runoff-dominated wetlands which lack predators. Using stoichiometric models, I generated predictions for how variation in environmental temperature and predation pressure would affect the N:P ratio recycled by fishes. Adult female G. marshi excretion N:P ratio was higher in runoff-dominated sites, which was consistent with predators driving increased consumption rates by G. marshi. This result was supported by a diet ration manipulation experiment in which G. marshi raised on an ad libitum diet excreted N:P at a lower ratio than fish raised on a restricted diet ration. To further support the impacts of predation on phenotypic diversification in G. marshi, I examined how body morphology varied among habitats and among closely related species. Both among and within species, predation had stronger effects on morphology than the physical environment. Overall, these results suggest that predation, not temperature, has strong effects on these phenotypic traits of aquatic consumers which can alter their role in ecosystem nutrient cycling through variation in consumption rates.

Contributors

Agent

Created

Date Created
  • 2017

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The costs and consequences of iridescent coloration in Anna's hummingbirds (Calypte anna)

Description

Colorful ornaments in animals often serve as sexually selected signals of quality. While pigment-based colors are well-studied in these regards, structural colors that result from the interaction of light with

Colorful ornaments in animals often serve as sexually selected signals of quality. While pigment-based colors are well-studied in these regards, structural colors that result from the interaction of light with photonic nanostructures are comparatively understudied in terms of their consequences in social contexts, their costs of production, and even the best way to measure them. Iridescent colors are some of the most brilliant and conspicuous colors in nature, and I studied the measurement, condition-dependence, and signaling role of iridescence in Anna's hummingbirds (Calypte anna). While most animal colors are easily quantified using well-established spectrophotometric techniques, the unique characteristics of iridescent colors present challenges to measurement and opportunities to quantify novel color metrics. I designed and tested an apparatus for careful control and measurement of viewing geometry and highly repeatable measurements. These measurements could be used to accurately characterize individual variation in iridescent Anna's hummingbirds to examine their condition-dependence and signaling role. Next, I examined the literature published to date for evidence of condition-dependence of structural colors in birds. Using meta-analyses, I found that structural colors of all three types - white, ultra-violet/blue, and iridescence - are significantly condition-dependent, meaning that they can convey information about quality to conspecifics. I then investigated whether iridescent colors were condition-dependent in Anna's hummingbirds both in a field correlational study and in an experimental study. Throughout the year, I found that iridescent feathers in both male and female Anna's hummingbirds become less brilliant as they age. Color was not correlated with body condition in any age/sex group. However, iridescent coloration in male Anna's hummingbirds was significantly affected by experimental protein in the diet during feather growth, indicating that iridescent color may signal diet quality. Finally, I examined how iridescent colors were used to mediate social competitions in male and female Anna's hummingbirds. Surprisingly, males that were less colorful won significantly more contests than more colorful males, and colorful males received more aggression. Less colorful males may be attempting to drive away colorful neighbors that may be preferred mates. Female iridescent ornament size and color was highly variable, but did not influence contest outcomes or aggression.

Contributors

Agent

Created

Date Created
  • 2012