Matching Items (21)
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- All Subjects: Ecology
- Creators: Wu, Jianguo
Description
The relationship between biodiversity and ecosystem functioning (BEF) is a central issue in ecology, and a number of recent field experimental studies have greatly improved our understanding of this relationship. Spatial heterogeneity is a ubiquitous characterization of ecosystem processes, and has played a significant role in shaping BEF relationships. The first step towards understanding the effects of spatial heterogeneity on the BEF relationships is to quantify spatial heterogeneity characteristics of key variables of biodiversity and ecosystem functioning, and identify the spatial relationships among these variables. The goal of our research was to address the following research questions based on data collected in 2005 (corresponding to the year when the initial site background information was conducted) and in 2008 (corresponding to the year when removal treatments were conducted) from the Inner Mongolia Grassland Removal Experiment (IMGRE) located in northern China: 1) What are the spatial patterns of soil nutrients, plant biodiversity, and aboveground biomass in a natural grassland community of Inner Mongolia, China? How are they related spatially? and 2) How do removal treatments affect the spatial patterns of soil nutrients, plant biodiversity, and aboveground biomass? Is there any change for their spatial correlations after removal treatments? Our results showed that variables of biodiversity and ecosystem functioning in the natural grassland community would present different spatial patterns, and they would be spatially correlated to each other closely. Removal treatments had a significant effect on spatial structures and spatial correlations of variables, compared to those prior to the removal treatments. The differences in spatial pattern of plant and soil variables and their correlations before and after the biodiversity manipulation may not imply that the results from BEF experiments like IMGRE are invalid. However, they do suggest that the possible effects of spatial heterogeneity on the BEF relationships should be critically evaluated in future studies.
ContributorsYuan, Fei (Author) / Wu, Jianguo (Thesis advisor) / Smith, Andrew T. (Committee member) / Rowe, Helen I (Committee member) / Arizona State University (Publisher)
Created2011
Description
Over the past century in the southwestern United States human actions have altered hydrological processes that shape riparian ecosystems. One change, release of treated wastewater into waterways, has created perennial base flows and increased nutrient availability in ephemeral or intermittent channels. While there are benefits to utilizing treated wastewater for environmental flows, there are numerous unresolved ecohydrological issues regarding the efficacy of effluent to sustain groundwater-dependent riparian ecosystems. This research examined how nutrient-rich effluent, released into waterways with varying depths to groundwater, influences riparian plant community development. Statewide analysis of spatial and temporal patterns of effluent generation and release revealed that hydrogeomorphic setting significantly influences downstream riparian response. Approximately 70% of effluent released is into deep groundwater systems, which produced the lowest riparian development. A greenhouse study assessed how varying concentrations of nitrogen and phosphorus, emulating levels in effluent, influenced plant community response. With increasing nitrogen concentrations, vegetation emerging from riparian seed banks had greater biomass, reduced species richness, and greater abundance of nitrophilic species. The effluent-dominated Santa Cruz River in southern Arizona, with a shallow groundwater upper reach and deep groundwater lower reach, served as a study river while the San Pedro River provided a control. Analysis revealed that woody species richness and composition were similar between the two systems. Hydric pioneers (Populus fremontii, Salix gooddingii) were dominant at perennial sites on both rivers. Nitrophilic species (Conium maculatum, Polygonum lapathifolium) dominated herbaceous plant communities and plant heights were greatest in effluent-dominated reaches. Riparian vegetation declined with increasing downstream distance in the upper Santa Cruz, while patterns in the lower Santa Cruz were confounded by additional downstream agricultural input and a channelized floodplain. There were distinct longitudinal and lateral shifts toward more xeric species with increasing downstream distance and increasing lateral distance from the low-flow channel. Patterns in the upper and lower Santa Cruz reaches indicate that water availability drives riparian vegetation outcomes below treatment facilities. Ultimately, this research informs decision processes and increases adaptive capacity for water resources policy and management through the integration of ecological data in decision frameworks regarding the release of effluent for environmental flows.
ContributorsWhite, Margaret Susan (Author) / Stromberg, Juliet C. (Thesis advisor) / Fisher, Stuart G. (Committee member) / White, Dave (Committee member) / Holway, James (Committee member) / Wu, Jianguo (Committee member) / Arizona State University (Publisher)
Created2011
Description
In 2010, a monthly sampling regimen was established to examine ecological differences in Saguaro Lake and Lake Pleasant, two Central Arizona reservoirs. Lake Pleasant is relatively deep and clear, while Saguaro Lake is relatively shallow and turbid. Preliminary results indicated that phytoplankton biomass was greater by an order of magnitude in Saguaro Lake, and that community structure differed. The purpose of this investigation was to determine why the reservoirs are different, and focused on physical characteristics of the water column, nutrient concentration, community structure of phytoplankton and zooplankton, and trophic cascades induced by fish populations. I formulated the following hypotheses: 1) Top-down control varies between the two reservoirs. The presence of piscivore fish in Lake Pleasant results in high grazer and low primary producer biomass through trophic cascades. Conversely, Saguaro Lake is controlled from the bottom-up. This hypothesis was tested through monthly analysis of zooplankton and phytoplankton communities in each reservoir. Analyses of the nutritional value of phytoplankton and DNA based molecular prey preference of zooplankton provided insight on trophic interactions between phytoplankton and zooplankton. Data from the Arizona Game and Fish Department (AZGFD) provided information on the fish communities of the two reservoirs. 2) Nutrient loads differ for each reservoir. Greater nutrient concentrations yield greater primary producer biomass; I hypothesize that Saguaro Lake is more eutrophic, while Lake Pleasant is more oligotrophic. Lake Pleasant had a larger zooplankton abundance and biomass, a larger piscivore fish community, and smaller phytoplankton abundance compared to Saguaro Lake. Thus, I conclude that Lake Pleasant was controlled top-down by the large piscivore fish population and Saguaro Lake was controlled from the bottom-up by the nutrient load in the reservoir. Hypothesis 2 stated that Saguaro Lake contains more nutrients than Lake Pleasant. However, Lake Pleasant had higher concentrations of dissolved nitrogen and phosphorus than Saguaro Lake. Additionally, an extended period of low dissolved N:P ratios in Saguaro Lake indicated N limitation, favoring dominance of N-fixing filamentous cyanobacteria in the phytoplankton community in that reservoir.
ContributorsSawyer, Tyler R (Author) / Neuer, Susanne (Thesis advisor) / Childers, Daniel L. (Committee member) / Sommerfeld, Milton (Committee member) / Arizona State University (Publisher)
Created2011
Description
The Northern Gulf of California is characterized by an extreme tidal range and temperature fluctuations between seasons, as well as a large variation in microhabitats along its shoreline. As a result, the intertidal regions exhibit a diverse and distinct collection of species that have adapted to these environmental conditions, with roughly 4.6 percent being endemic. Minimal knowledge of these ecosystems existed until the 1940’s, when the renowned author John Steinbeck accompanied marine biologist Edward Ricketts on an expedition with the purpose of documenting the biodiversity of the Sea of Cortez. Today, the majority of research in the Northern Gulf of California is directed by CEDO, the Intercultural Center for the Study of Deserts and Oceans. The purpose of this project is to compile a literature review of research on the intertidal areas of the Northern Gulf and produce an illustrated brochure that educates beach visitors on local biodiversity as a collaboration with CEDO and the Clean Beaches Committee of Puerto Peñasco. This brochure aims to increase respect and appreciation for these species, as increased tourism over the past few decades has led to detrimental effects on the ecosystem. Additionally, it serves to promote the success of the Blue Flag certification of El Mirador beach in front of Manny’s Beach Club.
ContributorsPotter, Jessica Noel (Co-author) / Potter, Jessica (Co-author) / Neuer, Susanne (Thesis director) / Mangin, Katrina (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
It is well known that deficiencies in key chemical elements (such as phosphorus, P) can reduce animal growth; however, recent empirical data have shown that high levels of dietary nutrients can also reduce animal growth. In ecological stoichiometry, this phenomenon is known as the "stoichiometric knife edge," but its underlying mechanisms are not well-known. Previous work has suggested that the crustacean zooplankter Daphnia reduces its feeding rates on phosphorus-rich food, causing low growth due to insufficient C (energy) intake. To test for this mechanism, feeding rates of Daphnia magna on algae (Scenedesmus acutus) differing in C:P ratio (P content) were determined. Overall, there was a significant difference among all treatments for feeding rate (p < 0.05) with generally higher feeding rates on P-rich algae. These data indicate that both high and low food C:P ratio do affect Daphnia feeding rate but are in contradiction with previous work that showed that P-rich food led to strong reductions in feeding rate. Additional experiments are needed to gain further insights.
ContributorsSchimpp, Sarah Ann (Author) / Elser, James (Thesis director) / Neuer, Susanne (Committee member) / Peace, Angela (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor) / School of Sustainability (Contributor)
Created2014-05
Description
The highly-social plateau pika (Lagomorpha: Ochotona curzoniae) excavates vast burrow complexes in alpine meadows on the Tibetan Plateau. Colonies of over 300 individuals/ha have been reported. As an ecosystem engineer, their burrowing may positively impact ecosystem health by increasing plant species diversity, enhancing soil mixing, and boosting water infiltration. However, pikas are commonly regarded as pests, and are heavily poisoned throughout their range. The underlying assumption of eradication programs is that eliminating pikas will improve rangeland quality and decrease soil erosion. This dissertation explores the link between plateau pikas and the alpine meadow ecosystem in Qinghai Province, PRC. This research uses both comparative field studies and theoretical modeling to clarify the role of pika disturbance. Specifically, these studies quantify the impact of pikas on nutrient cycling (via nutrient concentrations of vegetation and soil), hydrology (via water infiltration), local landscape properties (via spatial pattern description), and vascular plant communities (via species richness and composition). The competitive relationship between livestock and pikas is examined with a mathematical model. Results of this research indicate that pika colonies have both local and community level effects on water infiltration and plant species richness. A major contribution of pika disturbance is increased spatial heterogeneity, which likely underlies differences in the plant community. These findings suggest that the positive impact of plateau pikas on rangeland resources has been undervalued. In concurrence with other studies, this work concludes that plateau pikas provide valuable ecosystem services on the Tibetan Plateau.
ContributorsHogan, Brigitte Wieshofer (Author) / Smith, Andrew T. (Thesis advisor) / Anderies, J. Marty (Committee member) / Briggs, John M. (Committee member) / Stromberg, Juliet C. (Committee member) / Wu, Jianguo (Committee member) / Arizona State University (Publisher)
Created2010
Description
With a growing majority of humans living within cities and towns, urbanization is one of the most persistent drivers of change in global land use and challenges to sustainability and biodiversity conservation. The development of cities and towns can substantially shape local and regional environments in which wildlife communities persist. Although urbanization can negatively affect wildlife communities – through processes such as habitat fragmentation and non-native species introduction – cities can also provide resources to wildlife, such as through food, water, and space, creating potential opportunities for conservation. However, managing wildlife communities persisting in urbanizing landscapes requires better understanding of how urbanized landscapes influence the ability of wildlife to coexist with one another and with people at local and regional scales. In this dissertation, I addressed these research needs by evaluating the environmental and human factors driving dynamic wildlife community distributions and people’s attitudes towards wildlife. In my first two chapters,I used wildlife camera data collected from across the Phoenix Metropolitan Area, AZ to examine seasonal patterns of wildlife space use, species richness, and interspecific interactions across levels of urbanization with varying landscape characteristics, including plant productivity and spatial land use heterogeneity. Here I found that urbanization was a primary driver of wildlife community characteristics within the region, but that seasonal resource availability and landscape heterogeneity could have mediating influences that require further exploration. In my third chapter, I partnered
with wildlife researchers across North America to examine how relationships between urbanization and community composition vary among cities with distinct social-ecological characteristics, finding that effects of local urbanization were more negative in warmer, less vegetated, and more urbanized cities. In my fourth and final chapter, I explored the potential for human-wildlife coexistence by examining how various ideological, environmental, and sociodemographic factors influenced Phoenix area residents’ level of comfort living near different wildlife groups. Although I found that residents’ attitudes were primarily shaped by their relatively static wildlife values, comfort living near wildlife also depended on the characteristics of the neighboring environment, of the residents, and of the wildlife involved, indicating the potential for facilitating conditions for human-wildlife coexistence. Altogether, the findings of this dissertation suggest that the management of wildlife and their interactions with people within cities would benefit from more proactive and holistic consideration of the interacting environmental, wildlife, and human characteristics that influence the persistence of biodiversity within an increasingly urbanized world.
ContributorsHaight, Jeffrey Douglas (Author) / Hall, Sharon J (Thesis advisor) / Lewis, Jesse S (Thesis advisor) / Larson, Kelli L (Committee member) / Wu, Jianguo (Committee member) / Arizona State University (Publisher)
Created2023
Description
The efficiency of the ocean’s biological carbon pump is mediated by fast-sinking particles that quickly settle out of the euphotic zone. These particles are conventionally associated with micro- (> 20 µm) sized diatoms and coccolithophorids, thought to efficiently transport carbon to depth owing to their dense mineral structures, while pico- (< 2 µm) and nanophytoplankton (2-20 µm) are considered to contribute negligibly due to their small size and low sinking speed. Despite burgeoning evidence of their export, the mechanisms behind it remain poorly understood. The objective of this dissertation is to acquire a mechanistic understanding of the contribution of pico- and nanophytoplankton to particle fluxes. I tested the hypotheses that pico- and nanophytoplankton may be exported via the following pathways: 1) physical aggregation due to the production of sticky Transparent Exopolymeric Particles (TEP), mediated by interactions with heterotrophic bacteria, 2) attachment to lithogenic minerals, and 3) repackaging by zooplankton. I found that despite the traditional view of being too small to sink, pico- and nanophytoplankton form aggregates rich in TEP, allowing cells to scavenge lithogenic minerals and thus increase their effective size and density. I discovered that interactions with heterotrophic bacteria were significant in mediating the process of aggregation by influencing the production and/or the composition of the phytoplankton-derived TEP. Bacteria differentially influenced aggregation and TEP production; some species enhanced aggregation without affecting TEP production, and vice-versa. Finally, by determining the microbial composition of sinking particles in an open-ocean site, I found pico- and nanophytoplankton significantly associated with particles sourced from crustaceous zooplankton, suggesting that their export is largely mediated by mesozooplankton.
Overall, I show that the hypothesized mechanisms of pico- and nanophytoplankton export are not mutually exclusive, but instead occur subsequently. Given the right conditions for their aggregation in the natural environment, such as interactions with aggregation-enhancing heterotrophic bacteria and/or the presence of lithogenic minerals, their cells and aggregates can escape remineralization within the euphotic zone, and thus be susceptible to grazing by mesozooplankton export within fecal pellets. The results of this dissertation provide a mechanistic framework for the contribution of pico- and nanophytoplankton to ocean particle fluxes.
ContributorsCruz, Bianca Nahir (Author) / Neuer, Susanne (Thesis advisor) / Lomas, Michael W (Committee member) / Passow, Uta (Committee member) / Cadillo-Quiroz, Hinsby (Committee member) / Arizona State University (Publisher)
Created2021
Description
Heavy metals and persistent organic pollutants contribute to human health risks worldwide. Among the most common routes of exposure to pollutants for humans are through the consumption of contaminated water and food, with fish being among the greatest vectors for ingestion of heavy metals in humans, particularly mercury.This dissertation consists of three chapters with a central theme of investigating heavy metal and persistent organic pollutant concentrations in fish and corned beef, which are two commonly consumed food items in American Samoa. A literature review illustrated that historically the primary pollutants of concern in fish muscle tissue from American Samoa have been mercury, arsenic, and polycyclic aromatic hydrocarbon mixtures. To better understand the changes in heavy metals and persistent organic pollutants in fish, this study reports an updated data set, comparing concentrations in pollutants as they have changed over time. To further investigate pollutants in fish tissue, 77 locally caught and commonly consumed fish were analyzed for heavy metals and persistent organic pollutants, and baseline human health risk assessments were calculated for contaminants that had available oral reference doses. While in American Samoa collecting fish for contaminant analyses, it was realized that canned corned beef appeared to be more commonly consumed than fresh fish. An IRB approved consumption survey revealed that 89% of American Samoan adults regularly consume fish, which is the same percentage of people that reported eating canned corned beef, indicating a dramatic increase in this food item to their diet since its introduction in the 20th century.
Results of this study indicate that fish muscle tissue generally has higher heavy metal concentrations than canned corned beef, and that mercury continues to be a main contaminant of concern when consuming fresh and canned fish in American Samoa. While none of the heavy metal concentrations in corned beef exceeded calculated action levels, these foods might contribute to negative health outcomes in other ways. One of the main findings of this study is that either the presence or the ability to detect persistent organic pollutant concentrations are increasing in fish tissue and should be periodically monitored to adequately reflect current conditions.
ContributorsLewis, Tiffany Beth (Author) / Polidoro, Beth (Thesis advisor) / Neuer, Susanne (Thesis advisor) / Halden, Rolf (Committee member) / Schoon, Michael (Committee member) / Arizona State University (Publisher)
Created2023
Description
The genus Buellia remains one of the largest, poorly resolved genera of crustose lichens world-wide. A global revision is challenging because of its enormous diversity .As a step towards a more comprehensive revision, three easily separated groups were examined. Buellia sulphurica is easily recognized by its vivid yellow color, caused by rhizocarpic acid, a secondary metabolite rarely reported from the genus. The species has been considered endemic to the Galapagos, but it is morphologically and anatomically almost identical to B. xanthinula, a taxon previously described from Brazil. Moreover, both have rhizocarpic acid. Additionally, a specimen from Georgia with a similar morphology and anatomy with identical secondary chemistry has been examined here. Based on this research, it is discussed whether all three taxa represent a single species. Another aspect of the research presented here focused on species of Buellia that parasitize other lichens. It is generally assumed that they are strongly host-specific. Parasitic specimens of Buellia recently collected in the Great Basin are morphologically similar to taxa previously reported from Northern Europe, South America, and North America. Preliminary studies, comparing the material with specimens of B. uberior, B. miriquidica, B. malmei and B. imshaugii, suggest that the Great Basin material is best recognized as representatives of distinct, currently undescribed species. Finally, as part of this thesis a group of specimens from the Galapagos containing xanthones has been examined. This heterogeneous group represents an assemblage of taxa that are not necessarily closely related, but easily recognized by their bright yellow to orange UV-fluorescence and orange spot test reaction with sodium hypochlorite. For this group, morphological and anatomical characters were documented, and their secondary chemistry analyzed with thin-layer chromatography. For all three groups, i.e., the Buellia xanthinula-group, the parasitic species, and the ones with xanthones, detailed descriptions are provided.
ContributorsParrinello, Christian (Author) / Bungartz, Frank (Thesis advisor) / Wojciechowski, Martin (Committee member) / Pigg, Kathleen (Committee member) / Arizona State University (Publisher)
Created2024