Matching Items (3)
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- All Subjects: biodiversity
- Creators: Smith, Andrew T.
Description
Epidemiological theory normally does not predict host extinction from infectious disease because of a host density threshold below which pathogens cannot persist. However, host extinction can occur when a biotic or abiotic pathogen reservoir allows for density-independent transmission. Amphibians are facing global population decline and extinction from the emerging infectious disease chytridiomycosis, caused by the fungus Batrachochytrium dentrobatidis (Bd). I use the model species Eleutherodactylus coqui to assess the impact of Bd on terrestrial direct-developing frog species, a common life history in the tropics. I tested the importance of two key factors that might influence this impact and then used laboratory experiments and published field data to model population-level impacts of Bd on E. coqui. First, I assessed the ontogenetic susceptibility of E. coqui by exposing juvenile and adult frogs to the same pathogen strain and dose. Juveniles exposed to Bd had significantly lower survival rates compared with control juveniles, while adult frogs often cleared infection. Second, I conducted experiments to determine whether E. coqui can become infected with Bd indirectly from contact with zoospores shed onto vegetation by an infected frog and from direct exposure to an infected frog. Both types of transmission were observed, making this the first demonstration that amphibians can become infected indirectly in non-aquatic habitats. Third, I tested the hypothesis that artificially-maintained cultures of Bd attenuate in pathogenicity, an effect known for other fungal pathogens. Comparing two cultures of the same Bd strain with different passage histories revealed reduced zoospore production and disease-induced mortality rates for a susceptible frog species (Atelopus zeteki) but not for the less-susceptible E. coqui. Finally, I used a mathematical model to project the population-level impacts of chytridiomycosis on E. coqui. Model analysis showed that indirect transmission, combined with either a high rate of zoospore production or low rate of zoospore mortality, is required for Bd to drive E. coqui populations below an extinction threshold. High rates of transmission plus frequent re-infection could lead to poor recruitment of infected juveniles and population decline. My research adds further insight into how emerging infectious disease is contributing to the loss of amphibian biodiversity.
ContributorsLanghammer, Penny F. (Author) / Collins, James P. (Thesis advisor) / Brooks, Thomas M (Committee member) / Burrowes, Patricia A. (Committee member) / Anderies, John M (Committee member) / Escalante, Ananias A (Committee member) / Smith, Andrew T. (Committee member) / Arizona State University (Publisher)
Created2013
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
Balancing conservation goals and needs of local residents is always challenging. While some believe protected areas are a safe paradise for wildlife, others suggest that it is shortsighted to ignore the social and economic challenges faced by people who live adjacent to protected areas when addressing conservation objectives. This dissertation explores the link between biodiversity conservation and environmental education programs (EEPs) administered to residents of buffer zones adjacent to three protected areas in the Terai Arc Landscape, Nepal. Using surveys and interviews, this study examined 1) the influence of EEPs on attitudes of local people toward biodiversity conservation; 2) the influence of EEPs on conservation behavior; 3) the responses toward biodiversity conservation of local people residing in buffer zones who have received different levels of EEPs; and 4) the effect of EEPs on wildlife populations within adjacent protected areas. Local people who had participated in EEPs and attended school were more likely to express a positive attitude toward conservation goals than participants who had not participated in EEPs or had the opportunity to attend school. Participation in EEPs and level of education favored expressed behavior toward conservation goals, such as making contributions for conservation or supporting anti-poaching patrols. However, EEP participants and non-participants were equally likely to engage in activities that were at odds with positive conservation behavior, such as collecting fuel wood or killing wildlife to protect their farm or feed their families. A direct comparison of EEPs given by schools versus non-government organizations showed that EEPs were largely ineffective in promoting positive conservation attitudes and behaviors. Despite heavy poaching of charismatic species such as the greater one-horned rhinoceros or tiger over past decades, Nepal recently celebrated ‘zero poaching years’ in 2011 and 2013, largely due to increased anti-poaching enforcement. The relationship between EEPs and the decline in poaching is unclear, although local officials all claimed that EEPs played an important role. These results indicate that current administration of EEPs in Terai buffer zone communities is inadequate, while also providing evidence that properly administrated EEPs may become a valuable investment for these protected areas to achieve long-term success.
ContributorsShrestha, Samridhi (Author) / Smith, Andrew T. (Thesis advisor) / Minteer, Ben (Committee member) / Pearson, David (Committee member) / Nyaupane, Gyan (Committee member) / Budruk, Megha (Committee member) / Arizona State University (Publisher)
Created2015