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- All Subjects: Ecology
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 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
Description
Phosphorus (P), an essential nutrient for growth of all organisms, is often in limited biological supply for herbivore consumers compared to other elements, such as carbon (C). Ecological stoichiometry studies have assessed responses of filter-feeding zooplankton from the genus Daphnia to single and multi-species food resources that are P-limited, finding decreased growth as a result to changes in metabolic processes and feeding behavior. Conversely, recent laboratory studies have shown that P-rich algal food resources also result in decreased growth rates for Daphnia, though the possible mechanisms behind this maladaptive response is understudied. Moreover, no published study tests the existence of the “stoichiometric knife edge” hypothesis for low C:P under field conditions. To address this lack of information, I measured growth rate as well as respiration and ingestion rates for D. magna, D. pulicaria, and D. pulex that were fed natural lake seston experimentally enriched with different levels of PO43-. I found heterogeneous effects of high dietary P across Daphnia species. Growth rate responses for D. magna were strong and indicated a negative effect of high-P, most likely as a result to decreased ingestion rates that were observed. The seston treatments did not elicit significant growth rate responses for D. pulex and D. pulicaria, but significant responses to respiration rates were observed for all species. Consumer body stoichiometry, differences in seston C:P for each experiment, or differential assimilation by producer types may be driving these results. My study suggests that the stoichiometric knife edge documented in laboratory studies under low C:P conditions may not operate to the same degree when natural seston is the food source; diet diversity may be driving complex nuances for consumer performance that were previously overlooked.
ContributorsCurrier, Courtney M (Author) / Currier, James (Thesis advisor) / Harrison, Jon (Committee member) / Neuer, Susanne (Committee member) / Arizona State University (Publisher)
Created2015
Description
Hydrological models in arid and semi-arid ecosystems can be subject to high uncertainties. Spatial variability in soil moisture and evapotranspiration, key components of the water cycle, can contribute to model uncertainty. In particular, an understudied source of spatial variation is the effect of plant-plant interactions on water fluxes. At patch scales (plant and associated soil), plant neighbors can either negatively or positively affect soil water availability via competition or hydraulic redistribution, respectively. The aboveground microclimate can also be altered via canopy shading effects by neighbors. Across longer timescales (years), plants may adjust their physiological (water-use) traits in response to the neighbor-altered microclimate, which subsequently affects transpiration rates. The influence of physiological adjustments and neighbor-altered microclimate on water fluxes was assessed around Larrea tridentata in the Sonoran Desert. Field measurements of Larrea’s stomatal behavior and vertical root distributions were used to examine the effects of neighbors on Larrea’s physiological controls on transpiration. A modeling based approach was implemented to explore the sensitivity of evapotranspiration and soil moisture to neighbor effects. Neighbors significantly altered both above- and belowground physiological controls on evapotranspiration. Compared to Larrea growing alone, neighbors increased Larrea’s annual transpiration by up to 75% and 30% at the patch and stand scales, respectively. Estimates of annual transpiration were highly sensitive to the presence/absence of competition for water, and on seasonal timescales, physiological adjustments significantly influenced transpiration estimates. Plant-plant interactions can be a significant source of spatial variation in ecohydrological models, and both physiological adjustments to neighbors and neighbor effects on microclimate affect small scale (patch to ecosystem) water fluxes.
ContributorsKropp, Heather (Author) / Ogle, Kiona (Thesis advisor) / Hultine, Kevin (Committee member) / Sala, Osvaldo (Committee member) / Vivoni, Enrique (Committee member) / Wojciechowski, Martin (Committee member) / Arizona State University (Publisher)
Created2015
Description
The family Cactaceae is extremely diverse and has a near global distribution yet very little has been described regarding the community of viruses that infect or are associated with cacti. This research characterizes the diversity of viruses associated with Cactaceae plants and their evolutionary aspects. Five viruses belonging to the economically relevant plant virus family Geminiviridae were identified, initially, two novel divergent geminiviruses named Opuntia virus 1 (OpV1) and Opuntia virus 2 (OpV2) and Opuntia becurtovirus, a new strain within the genus Becurtovirus. These three viruses were also found in co-infection. In addition, two known geminiviruses, the squash leaf curl virus (SLCV) and watermelon chlorotic stunt virus (WCSV) were identified infecting Cactaceae plants and other non-cactus plants in the USA and Mexico. Both SLCV and WCSV are known to cause severe disease in cultivated Cucurbitaceae plants in the USA and Middle East, respectively. This study shows that WCSV was introduced in the America two times, and it is the first identification of this virus in the USA, demonstrating is likely more widespread in North America. These findings along with the Opuntia becurtovirus are probable events of spill-over in agro-ecological interfaces. A novel circular DNA possibly bipartite plant-infecting virus that encodes protein similar to those of geminiviruses was also identified in an Opuntia discolor plant in Brazil, named utkilio virus, but it is evolutionary distinct likely belonging to a new taxon. Viruses belonging to the ssDNA viral family Genomoviridae are also described and those thus far been associated with fungi hosts, so it is likely the ones identified in plants are associated with their phytobiome. Overall, the results of this project provide a molecular and biological characterization of novel geminiviruses and genomoviruses associated with cacti as well as demonstrate the impact of agro-ecological interfaces in the spread of viruses from or to native plants. It also highlights the importance of viral metagenomics studies in exploring virus diversity and evolution given then amount of virus diversity identified. This is important for conservation and management of cacti in a global scale, including the relevance of controlled movement of plants within countries.
ContributorsSalgado Fontenele, Rafaela (Author) / Varsani, Arvind (Thesis advisor) / Wilson, Melissa (Committee member) / Majure, Lucas (Committee member) / Van Doorslaer, Koenraad (Committee member) / Wojciechowski, Martin (Committee member) / Arizona State University (Publisher)
Created2021