Matching Items (227)
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There is a growing consensus that photodegradation accelerates litter decomposition in drylands, but the mechanisms are not well understood. In a previous field study examining how exposure to solar radiation affects decomposition of 12 leaf litter types over 34 months in the Sonoran Desert, litter exposed to UV/blue wavebands of

There is a growing consensus that photodegradation accelerates litter decomposition in drylands, but the mechanisms are not well understood. In a previous field study examining how exposure to solar radiation affects decomposition of 12 leaf litter types over 34 months in the Sonoran Desert, litter exposed to UV/blue wavebands of solar radiation decayed faster. The concentration of water-soluble compounds was higher in decayed litter than in new (recently senesced) litter, and higher in decayed litter exposed to solar radiation than other decayed litter. Microbial respiration of litter incubated in high relative humidity for 1 day was greater in decayed litter than new litter and greatest in decayed litter exposed to solar radiation. Respiration rates were strongly correlated with decay rates and water-soluble concentrations of litter. The objective of the current study was to determine why respiration rates were higher in decayed litter and why this effect was magnified in litter exposed to solar radiation. First, I evaluated whether photodegradation enhanced the quantity of dissolved organic carbon (DOC) in litter by comparing DOC concentrations of photodegraded litter to new litter. Second, I evaluated whether photodegradation increased the quality of DOC for microbial utilization by measuring respiration of leachates with equal DOC concentrations after applying them to a soil inoculum. I hypothesized that water vapor sorption may explain differences in respiration among litter age or sunlight exposure treatments. Therefore, I assessed water vapor sorption of litter over an 8-day incubation in high relative humidity. Water vapor sorption rates over 1 and 8 days were slower in decayed than new litter and not faster in photodegraded than other decayed litter. However, I found that 49-78% of the variation in respiration could be explained by the relative amount of water litter absorbed over 1 day compared to 8 days, a measure referred to as relative water content. Decayed and photodegraded litter had higher relative water content after 1 day because it had a lower water-holding capacity. Higher respiration rates of decayed and photodegraded litter were attributed to faster microbial activation due to greater relative water content of that litter.
ContributorsBliss, Michael Scott (Author) / Day, Thomas A. (Thesis advisor) / Garcia-Pichel, Ferran (Committee member) / Throop, Heather L. (Committee member) / Arizona State University (Publisher)
Created2019
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Although many studies have identified environmental factors as primary drivers of bird richness and abundance, there is still uncertainty about the extent to which climate, topography and vegetation influence richness and abundance patterns seen in local extents of the northern Sonoran Desert. I investigated how bird richness and abundance differed

Although many studies have identified environmental factors as primary drivers of bird richness and abundance, there is still uncertainty about the extent to which climate, topography and vegetation influence richness and abundance patterns seen in local extents of the northern Sonoran Desert. I investigated how bird richness and abundance differed between years and seasons and which environmental variables most influenced the patterns of richness and abundance in the Greater Phoenix Metropolitan Area.

I compiled a geodatabase of climate, bioclimatic (interactions between precipitation and temperature), vegetation, soil, and topographical variables that are known to influence both richness and abundance and used 15 years of bird point count survey data from urban and non-urban sites established by Central Arizona–Phoenix Long-Term Ecological Research project to test that relationship. I built generalized linear models (GLM) to elucidate the influence of each environmental variable on richness and abundance values taken from 47 sites. I used principal component analysis (PCA) to reduce 43 environmental variables to 9 synthetic factors influenced by measures of vegetation, climate, topography, and energy. I also used the PCA to identify uncorrelated raw variables and modeled bird richness and abundance with these uncorrelated environmental variables (EV) with GLM.

I found that bird richness and abundance were significantly different between seasons, but that richness and winter abundance were not significantly different across years. Bird richness was most influenced by soil characteristics and vegetation while abundance was most influenced by vegetation and climate. Models using EV as independent variables consistently outperformed those models using synthetically produced components from PCA. The results suggest that richness and abundance are both driven by climate and aspects of vegetation that may also be influenced by climate such as total annual precipitation and average temperature of the warmest quarter. Annual oscillations of bird richness and abundance throughout the urban Phoenix area seem to be strongly associated with climate and vegetation.
ContributorsBoehme, Cameron (Author) / Albuquerque, Fabio Suzart (Thesis advisor) / Bateman, Heather L (Committee member) / Saul, Steven E (Committee member) / Arizona State University (Publisher)
Created2019
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Soil organic carbon (SOC) is a critical component of the global carbon (C) cycle, accounting for more C than the biotic and atmospheric pools combined. Microbes play an important role in soil C cycling, with abiotic conditions such as soil moisture and temperature governing microbial activity and subsequent soil C

Soil organic carbon (SOC) is a critical component of the global carbon (C) cycle, accounting for more C than the biotic and atmospheric pools combined. Microbes play an important role in soil C cycling, with abiotic conditions such as soil moisture and temperature governing microbial activity and subsequent soil C processes. Predictions for future climate include warmer temperatures and altered precipitation regimes, suggesting impacts on future soil C cycling. However, it is uncertain how soil microbial communities and subsequent soil organic carbon pools will respond to these changes, particularly in dryland ecosystems. A knowledge gap exists in soil microbial community responses to short- versus long-term precipitation alteration in dryland systems. Assessing soil C cycle processes and microbial community responses under current and altered precipitation patterns will aid in understanding how C pools and cycling might be altered by climate change. This study investigates how soil microbial communities are influenced by established climate regimes and extreme changes in short-term precipitation patterns across a 1000 m elevation gradient in northern Arizona, where precipitation increases with elevation. Precipitation was manipulated (50% addition and 50% exclusion of ambient rainfall) for two summer rainy seasons at five sites across the elevation gradient. In situ and ex situ soil CO2 flux, microbial biomass C, extracellular enzyme activity, and SOC were measured in precipitation treatments in all sites. Soil CO2 flux, microbial biomass C, extracellular enzyme activity, and SOC were highest at the three highest elevation sites compared to the two lowest elevation sites. Within sites, precipitation treatments did not change microbial biomass C, extracellular enzyme activity, and SOC. Soil CO2 flux was greater under precipitation addition treatments than exclusion treatments at both the highest elevation site and second lowest elevation site. Ex situ respiration differed among the precipitation treatments only at the lowest elevation site, where respiration was enhanced in the precipitation addition plots. These results suggest soil C cycling will respond to long-term changes in precipitation, but pools and fluxes of carbon will likely show site-specific sensitivities to short-term precipitation patterns that are also expected with climate change.
ContributorsMonus, Brittney (Author) / Throop, Heather L (Thesis advisor) / Ball, Becky A (Committee member) / Hultine, Kevin R (Committee member) / Munson, Seth M (Committee member) / Arizona State University (Publisher)
Created2019
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Emerging infectious diseases (EIDs) in vulnerable populations are a proposed cause of reduced global biodiversity due to local and regional extinctions. Chytridiomycosis, a fungal disease caused by Batrachochytrium dendrobatidis (Bd), is affecting amphibian populations worldwide.

Chapter 1 of this thesis reports using lab-raised larval tiger salamanders (Ambystoma tigrinum nebulosum), collected

Emerging infectious diseases (EIDs) in vulnerable populations are a proposed cause of reduced global biodiversity due to local and regional extinctions. Chytridiomycosis, a fungal disease caused by Batrachochytrium dendrobatidis (Bd), is affecting amphibian populations worldwide.

Chapter 1 of this thesis reports using lab-raised larval tiger salamanders (Ambystoma tigrinum nebulosum), collected as eggs, to test if Bd infects them. Bd infects metamorphosed tiger salamanders; however, it is currently unknown if larvae can be infected by Bd. Adult frogs tend to host Bd on ventral surfaces and hind legs while tadpoles host Bd in keratinized mouthparts. No research has considered differences in infection between life stages of salamanders. It was hypothesized that Bd can colonize larvae in the same manner as metamorphosed animals. Larval salamanders were inoculated to test if Bd concentrations differ among body regions in larvae compared to metamorphosed salamanders. Larvae can carry Bd with the concentration of Bd varying between body region.

Chapter 2 report using native tiger salamanders (Ambystoma tigrinum nebulosum), from northern Arizona and Bd as a study system to test if Bd is native or introduced to Arizona. It was hypothesized that Bd is not endemic to Arizona, but is introduced. There are multiple hypotheses regarding potential routes Bd may have traveled through Arizona and into Mexico. These hypotheses were tested using the Kaibab Plateau in Coconino County, Arizona, as a study site. The plateau is isolated from surrounding areas by the Grand Canyon to the south and the Vermillion Cliffs to the north serving as major biogeographical barriers. It is hypothesized that tiger salamanders are not dispersing into or out of the Kaibab Plateau due to geological restrictions. Bd, therefore, should not be present on salamanders on the Kaibab Plateau due to geological restriction. Tiger salamanders in stock tanks located on the Kaibab as well as preserved museum specimens housed in the Arizona State University Natural History Collection were sampled. The results indicate that Bd occurs at low levels on Kaibab Plateau tiger salamanders.
ContributorsOtsuru, Shinji Author (Author) / Collins, James P. (Thesis advisor) / Davidson, Elizabeth (Committee member) / Pratt, Stephen (Committee member) / Arizona State University (Publisher)
Created2019
Description
There is an ongoing debate around the extent that anthropogenic processes influence both plant species distribution dynamics and plant biodiversity patterns. Past human food use may leave a strong legacy on not only the extent that food plants are dispersed and fill their potential geographic ranges, but also on food

There is an ongoing debate around the extent that anthropogenic processes influence both plant species distribution dynamics and plant biodiversity patterns. Past human food use may leave a strong legacy on not only the extent that food plants are dispersed and fill their potential geographic ranges, but also on food plant species richness in areas that have been densely populated by humans through time. The persistent legacy of plant domestication on contemporary species composition has been suggested to be significant in some regions. However, little is known about the effects that past human food use has had on the biogeography of the Sonoran Desert despite its rich cultural diversity and species richness. I used a combination of ecoinformatics, ethnobotanical, and archaeological data sources to quantitatively assess the impacts of pre-Columbian, and in some cases, more recent, human-mediated dispersal of food plants on the Sonoran Desert landscape. I found that (i) food plants do fill more of their potential geographic ranges than their un-used congeners, and that polyploidy, growth form, and life form are correlated with range filling and past food usage. I also found that (ii) both pre-Columbian and contemporary human population presence are correlated with relative food plant species richness. Thus, both past human food use and contemporary human activities may have influenced the geographic distribution of food plants at regional scales as well as species richness patterns. My research emphasizes that there is an interplay between ecological and anthropogenic processes, and that, therefore, humans must be considered as part of the landscape and included in ecological models.
ContributorsFlower, Carolyn (Author) / Blonder, Benjamin (Thesis advisor) / Hodgson, Wendy (Committee member) / Peeples, Matthew (Committee member) / Salywon, Andrew (Committee member) / Arizona State University (Publisher)
Created2019
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Nitrogen is an essential, often limiting, element for biological growth that can act as a pollutant if present in excess. Nitrogen is primarily transported by water from uplands to streams and eventually to recipient lakes, estuaries, and wetlands, but can be modulated by biological uptake and transformation along these flowpaths.

Nitrogen is an essential, often limiting, element for biological growth that can act as a pollutant if present in excess. Nitrogen is primarily transported by water from uplands to streams and eventually to recipient lakes, estuaries, and wetlands, but can be modulated by biological uptake and transformation along these flowpaths. As a result, nitrogen can accumulate in aquatic ecosystems if supply is high or if biological retention is low. Dryland and urban ecosystems offer interesting contrasts in water supply, which limits transport and biological activity in drylands, and nitrogen supply that increases with human activity. In my dissertation, I ask: What is the relative balance among nitrogen retention, removal, and transport processes in dryland watersheds, and what is the fate of exported nitrogen? My dissertation research demonstrates that water is a major control on where and when nitrogen is retained and removed versus exported to downstream ecosystems. I used a mass-balance model based on synoptic surveys to study seasonal and spatial patterns in nitrate loading to a dryland stream network. I found that irrigation diversions transport nitrate from agricultural areas to the stream network year-round, even during dry seasons, and are an important driver of nitrate loading. I further explored how seasonal precipitation influences flood nutrient export in an intermittent desert stream by coupling long-term data of flood-water chemistry with stream discharge and precipitation data. I found that higher precipitation prior to a flood fills water storage sites in the catchment, leading to larger floods. In addition, higher antecedent precipitation stimulates biological nitrogen retention in the uplands, leading to lower nitrogen concentration in floods. Finally, I evaluated the consequences of nitrogen export from watersheds on how urban wetlands attenuate nitrate through denitrification that permanently removes nitrogen, and dissimilatory nitrate reduction to ammonium (DNRA) that retains nitrogen in another biologically reactive form. I found that DNRA becomes proportionally more important with low nitrate concentration, thereby retaining nitrogen as ammonium. Collectively, my dissertation research addresses how dryland and urban ecosystems can be integrated into models of watershed nitrogen cycling.

ContributorsHandler, Amalia Marie Baiyor (Author) / Grimm, Nancy (Thesis advisor) / Helton, Ashley M (Committee member) / Hartnett, Hilairy E (Committee member) / Ruddell, Benjamin L (Committee member) / Arizona State University (Publisher)
Created2019
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Climate change is increasing global surface temperatures, intensifying droughts and increasing rainfall variation, particularly in drylands. Understanding how dryland plant communities respond to climate change-induced rainfall changes is crucial for implementing effective conservation strategies. Concurrent with climate change impacts on drylands is woody encroachment: an increase in abundance of woody

Climate change is increasing global surface temperatures, intensifying droughts and increasing rainfall variation, particularly in drylands. Understanding how dryland plant communities respond to climate change-induced rainfall changes is crucial for implementing effective conservation strategies. Concurrent with climate change impacts on drylands is woody encroachment: an increase in abundance of woody plant species in areas formerly dominated by grasslands or savannahs. For example, the woody plant, Prosopis velutina (velvet mesquite), has encroached into grasslands regionally over the past century. From an agricultural perspective, P. velutina is an invasive weed that hinders cattle forage. Understanding how P. velutina will respond to climate change-induced rainfall changes can be useful for management and conservation efforts. Prosopis velutina was used to answer the following question: Is there a significant interactive effect of mean soil water moisture content and pulse frequency on woody seedling survival and growth in dryland ecosystems? There were 256 P. velutina seedlings sourced from the Santa Rita Experimental Range in southern Arizona grown under four watering treatments where mean and pulse frequency were manipulated over two months. Data were collected on mortality, stem height, number of leaves, instantaneous gas exchange, chlorophyll fluorescence, biomass, and the leaf carbon to nitrogen (C:N) ratio. Mortality was low across treatments. Pulse frequency had less impact across response variables than the mean amount of water received. This may indicate that P. velutina seedlings are relatively insensitive to rainfall timing and are more responsive to rainfall amount. Prosopis velutina in the low mean soil moisture treatments lost a majority of their leaves and had greater biomass allocation to roots. Prosopis velutina’s ability to survive in low soil moisture conditions and invest in root biomass can allow it to persist as drylands are further affected by climate change. Prosopis velutina could benefit ecosystems where native plants are at risk due to rainfall variation if P. velutina occupies a similar niche space. Due to conflicting viewpoints of P. velutina as an invasive species, it’s important to examine P. velutina from both agricultural and conservation perspectives. Further analysis on the benefits to P. velutina in these ecosystems is recommended.
ContributorsDavis, Ashley R. (Author) / Throop, Heather (Thesis advisor) / Hultine, Kevin (Committee member) / Sala, Osvaldo (Committee member) / Arizona State University (Publisher)
Created2020
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ABSTRACT

Human and wildlife behavior, governance, and economics are often cited obstacles to wildlife conservation. Accordingly, conservation research has historically been conducted in the exterior terrains of behavior and systems, which can be empirically observed or known through systemic analysis and applied through institutional or technical fixes. However, conservation interventions are

ABSTRACT

Human and wildlife behavior, governance, and economics are often cited obstacles to wildlife conservation. Accordingly, conservation research has historically been conducted in the exterior terrains of behavior and systems, which can be empirically observed or known through systemic analysis and applied through institutional or technical fixes. However, conservation interventions are failing because they do not adequately address the influence of individual and collective interior phenomena including psychological states, worldviews, values, and identities of stakeholders, which can bear decisively on conservation outcomes.

This critical analysis of wildlife conservation science and the social and political histories of Southwestern landscapes illustrates the mechanism of social, cultural, and media narrative linking four irreducible perspectives of the natural world: the I, WE, IT and ITS, or the psychological, cultural, behavioral and structural/systemic terrains, which ground contemporary conservation. Through the conceptual [Re]animation of conservation, this research justifies a more-than-human approach to wildlife conservation that resists the ontological privilege of the human and contemplates human and non-human animals as vitally linked in their mutually relational, perceptual and material environments. The approach extends the human to the natural environment and also accounts for the individual and social needs and perspectives of wild animals, which shape their adaptation to changing environments and conservation interventions.

A qualitative analysis of emotion, metaphor, and narrative utilizing an Integral Ecology framework explores how psychological and cultural terrains link to, and influence, the behavioral and systemic terrains of Mexican gray wolf (Canis lupus baileyi) conservation in the U.S. Southwest. This research disentangles and comprehensively maps influential elements in the four terrains; enhancing relational knowledge on human-predator coexistence and conservation governance in the Southwest.
ContributorsHagy Ferguson, Anita Dawn (Author) / Bolin, Bob (Thesis advisor) / BurnSilver, Shauna (Committee member) / Eder, James (Committee member) / Chhetri, Netra (Committee member) / Arizona State University (Publisher)
Created2019
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Global biodiversity is threatened by anthropogenic impacts, as the global population becomes increasingly urbanized. Conservation researchers and practitioners increasingly recognize the potential of cities to support biodiversity and foster human-nature interactions. However, further understanding of social and ecological mechanisms driving change in urban biodiversity over time is needed. In this

Global biodiversity is threatened by anthropogenic impacts, as the global population becomes increasingly urbanized. Conservation researchers and practitioners increasingly recognize the potential of cities to support biodiversity and foster human-nature interactions. However, further understanding of social and ecological mechanisms driving change in urban biodiversity over time is needed. In this dissertation, I first synthesized evidence for the urban homogenization hypothesis, which proposes that cities are more similar across space and time than are the natural communities they replace. I found that approaches to testing urban homogenization varied widely, but there is evidence for convergence at regional spatial scales and for some taxa. This work revealed a lack of long-term urban studies, as well as support for social and ecological mechanisms driving homogenization.

Building from this systematic literature review, I tested the effects of a long-term nutrient enrichment experiment in urban and near-urban desert preserves to evaluate indirect urban impacts on natural plant communities over time. Urban preserves and nitrogen-fertilized plots supported fewer annual wildflower species, limiting their effectiveness for biodiversity conservation and nature provisioning for urban residents.

Finally, I conducted research on residential yards in Phoenix, Arizona, to explore the effects of individual management behavior on urban plant community dynamics. Using a front yard vegetation survey repeated at three time points and a paired social survey, I asked, to what extent are yard plant communities dynamic over time, and how do attitudes and parcel characteristics affect native plant landscaping? Front yard woody plant communities experienced high turnover on a decadal scale, indicating that these managed communities are dynamic and capable of change for conservation benefit. Residents held positive attitudes toward native plants, but cultivated few in their yards. Priorities such as desired functional traits, attitudes toward native plants, and household income predicted native plant abundance, while knowledge of native plants did not.

This body of work contributes to the growing understanding of how urban ecosystems change over time in response to local- and city-scale impacts, demonstrating opportunities to engage urban residents and land managers in local conservation action to improve the value of cities for people and biodiversity.

ContributorsWheeler, Megan Michele (Author) / Hall, Sharon J (Thesis advisor) / Larson, Kelli L (Committee member) / Grimm, Nancy (Committee member) / Cavender-Bares, Jeannine (Committee member) / Arizona State University (Publisher)
Created2020
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Description
Land use change driven by human population expansion continues to influence

the integrity and configuration of riparian corridors worldwide. Wildlife viability in semi-arid regions depend heavily on the connectivity of riparian corridors, since water is the primary limiting resource. The Madrean Archipelago in northern Mexico and southwestern United States (US) is

Land use change driven by human population expansion continues to influence

the integrity and configuration of riparian corridors worldwide. Wildlife viability in semi-arid regions depend heavily on the connectivity of riparian corridors, since water is the primary limiting resource. The Madrean Archipelago in northern Mexico and southwestern United States (US) is a biodiversity hotspot that supports imperiled wildlife like jaguar (Panthera onca) and ocelot (Leopardus pardalis). Recent and ongoing infrastructure developments in the historically understudied US-México borderlands region, such as the border wall and expansion of Federal Highway 2, are altering wildlife movement and disconnecting essential habitat.

I used wildlife cameras to assess species occupancy, abundance, and related habitat variables affecting the use of washes as corridors for mammals in semi-arid Los Ojos (LO), a private ranch within a 530 km2 priority conservation area in Sonora, México located south of the border and Federal Highway 2. From October 2018 to April 2019, I deployed 21 wildlife cameras in five different riparian corridors within LO. I used single- season occupancy models and Royal Nichols abundance models to explore the relationship between habitat variables and use of riparian corridors by mammal communities of conservation concern within this region.

Twenty-one mammal species were recorded in the study area, including American black bear (Ursus americanus), white-tailed deer (Odocoileus virginianus) and the first sighting of jaguar (Panthera onca) in this region in 25 years. For the 11 medium- and large-bodied mammals recorded, habitat variables related to perennial river characteristics (distance to river, weekly water, and site width) and remoteness (distance from highway, elevation, and NDVI) were important for occupancy, but the direction of the relationship varied by species. For commonly observed species such as mountain lion (Puma concolor) and white-nosed coati (Nasua narica), topographic variety was highly informative for species abundance. These results highlight the importance of habitat diversity when identifying corridors for future protection to conserve wildlife communities in semi-arid regions. Additionally, this study provides robust evidence in support of mitigation measures (e.g. funnel fencing, over- or under- passes) along Federal Highway 2, and other barriers such as the border wall, to facilitate wildlife connectivity.
ContributorsRagan, Kinley (Author) / Hall, Sharon J (Thesis advisor) / Schipper, Jan (Thesis advisor) / Bateman, Heather L (Committee member) / Arizona State University (Publisher)
Created2020