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- All Subjects: Conservation Biology
- 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
As much as 40% of the world's human population relies on rivers which originate on the Qinghai-Tibetan Plateau (QTP) (Xu et al. 2009, Immerzeel et al. 2010). However, the high alpine grasslands where these rivers emanate are at a crossroads. Fed by seasonal monsoon rains and glacial runoff, these rivers' frequent flooding contributes to massive losses of life and property downstream (Varis et al. 2012). Additionally, upstream grasslands, which regulate the flow of these rivers, are considered to be deteriorating (Harris 2010). This thesis examines the regional vulnerability of these rivers and highlights the impacts of several policy responses, finding that both climate change and grassland degradation pose significant challenges to Asia's water security. Additionally, I suggest that many of the responses elicited by policy makers to meet these challenges have failed. One of these policies has been the poisoning of a small, endemic, burrowing mammal and keystone species, the plateau pika (Ochotona curzoniae) (Smith and Foggin 1999). Contrary to their putative classification as a pest (Fan et al. 1999), I show that the plateau pika is instead an ecosystem engineer that actively increases the infiltration rate of water on the QTP with concomitant benefits to both local ecosystems and downstream hydrological processes.
ContributorsWilson, Maxwell (Author) / Smith, Andrew T. (Thesis advisor) / Wu, Jiangou (Committee member) / Hall, Sharon J. (Committee member) / Arizona State University (Publisher)
Created2012
Description
The Great Bustard (Otis tarda) is an iconic species of the temperate grasslands of Europe and Asia, a habitat that is among the least protected ecosystems in the world. A distinct subspecies, the Asian Great Bustard (O. t. dybowskii), is poorly understood due to its wary nature and remote range in Siberia, Mongolia, and northern China. This subspecies is now endangered by rapid development.
Using satellite telemetry and remote sensing, I investigated three aspects of the Asian Great Bustard’s ecology critical to its conservation: migratory routes, migratory cues, and habitat use patterns. I found that Asian Great Bustards spent one-third of the year on a 2000 km migratory pathway, a distance twice as far as has previously been recorded for the species. Tracked individuals moved nomadically over large winter territories and did not repeat migratory stopovers, complicating conservation planning. Migratory timing was variable and migratory movements were significantly correlated with weather cues. Specifically, bustards migrated on days when wind support was favorable and temperature presaged warmer temperatures on the breeding grounds (spring) or advancing winter weather (fall). On the breeding grounds, Asian Great Bustards used both steppe and wheat agriculture habitat. All recorded reproductive attempts failed, regardless of habitat in which the nest was placed. Agricultural practices are likely to intensify in the coming decade, which would present further challenges to reproduction. The distinct migratory behavior and habitat use patterns of the Asian Great Bustard are likely adaptations to the climate and ecology of Inner Asia and underscore the importance of conserving these unique populations.
My research indicates that conservation of the Asian Great Bustard will require a landscape-level approach. This approach should incorporate measures at the breeding grounds to raise reproductive success, alongside actions on the migratory pathway to ensure appropriate habitat and reduce adult mortality. To secure international cooperation, I proposed that an increased level of protection should be directed toward the Great Bustard under the Convention on Migratory Species (CMS). That proposal, accepted by the Eleventh Conference of Parties to CMS, provides recommendations for conservation action and illustrates the transdisciplinary approach I have taken in this research.
Using satellite telemetry and remote sensing, I investigated three aspects of the Asian Great Bustard’s ecology critical to its conservation: migratory routes, migratory cues, and habitat use patterns. I found that Asian Great Bustards spent one-third of the year on a 2000 km migratory pathway, a distance twice as far as has previously been recorded for the species. Tracked individuals moved nomadically over large winter territories and did not repeat migratory stopovers, complicating conservation planning. Migratory timing was variable and migratory movements were significantly correlated with weather cues. Specifically, bustards migrated on days when wind support was favorable and temperature presaged warmer temperatures on the breeding grounds (spring) or advancing winter weather (fall). On the breeding grounds, Asian Great Bustards used both steppe and wheat agriculture habitat. All recorded reproductive attempts failed, regardless of habitat in which the nest was placed. Agricultural practices are likely to intensify in the coming decade, which would present further challenges to reproduction. The distinct migratory behavior and habitat use patterns of the Asian Great Bustard are likely adaptations to the climate and ecology of Inner Asia and underscore the importance of conserving these unique populations.
My research indicates that conservation of the Asian Great Bustard will require a landscape-level approach. This approach should incorporate measures at the breeding grounds to raise reproductive success, alongside actions on the migratory pathway to ensure appropriate habitat and reduce adult mortality. To secure international cooperation, I proposed that an increased level of protection should be directed toward the Great Bustard under the Convention on Migratory Species (CMS). That proposal, accepted by the Eleventh Conference of Parties to CMS, provides recommendations for conservation action and illustrates the transdisciplinary approach I have taken in this research.
ContributorsKessler, Aimee (Author) / Smith, Andrew T. (Thesis advisor) / Brown, David (Committee member) / Franklin, Janet (Committee member) / McGraw, Kevin (Committee member) / Wu, Jianguo (Committee member) / Arizona State University (Publisher)
Created2015
Description
Context – Urbanization can have negative effects on bat habitat use through the loss and isolation of habitat even for volant bats. Yet, how bats respond to the changing landscape composition and configuration of urban environments remains poorly understood.
Objective – This study examines the relationship between bat habitat use and landscape pattern across multiple scales in the Phoenix metropolitan region. My research explores how landscape composition and configuration affects bat activity, foraging activity, and species richness (response variables), and the distinct habitats that they use.
Methods – I used a multi-scale landscape approach and acoustic monitoring data to create predictive models that identified the key predictor variables across multiple scales within the study area. I selected three scales with the intent of capturing the landscape, home range, and site scales, which may all be relevant for understanding bat habitat use.
Results – Overall, class-level metrics and configuration metrics best explained bat habitat use for bat species associated with this urban setting. The extent and extensiveness of water (corresponding to small water bodies and watercourses) were the most important predictor variables across all response variables. Bat activity was predicted to be high in native vegetation remnants, and low in native vegetation at the city periphery. Foraging activity was predicted to be high in fine-scale land cover heterogeneity. Species richness was predicted to be high in golf courses, and low in commercial areas. Bat habitat use was affected by urban landscape pattern mainly at the landscape and site scale.
Conclusions – My results suggested in hot arid urban landscapes water is a limiting factor for bats, even in urban landscapes where the availability of water may be greater than in outlying native desert habitat. Golf courses had the highest species richness, and included the detection of the uncommon pocketed free-tailed bat (Nyctinomops femorosaccus). Water cover types had the second highest species richness. Golf courses may serve as important stop-overs or refuges for rare or elusive bats. Urban waterways and golf courses are novel urban cover types that can serve as compliments to urban preserves, and other green spaces for bat conservation.
Objective – This study examines the relationship between bat habitat use and landscape pattern across multiple scales in the Phoenix metropolitan region. My research explores how landscape composition and configuration affects bat activity, foraging activity, and species richness (response variables), and the distinct habitats that they use.
Methods – I used a multi-scale landscape approach and acoustic monitoring data to create predictive models that identified the key predictor variables across multiple scales within the study area. I selected three scales with the intent of capturing the landscape, home range, and site scales, which may all be relevant for understanding bat habitat use.
Results – Overall, class-level metrics and configuration metrics best explained bat habitat use for bat species associated with this urban setting. The extent and extensiveness of water (corresponding to small water bodies and watercourses) were the most important predictor variables across all response variables. Bat activity was predicted to be high in native vegetation remnants, and low in native vegetation at the city periphery. Foraging activity was predicted to be high in fine-scale land cover heterogeneity. Species richness was predicted to be high in golf courses, and low in commercial areas. Bat habitat use was affected by urban landscape pattern mainly at the landscape and site scale.
Conclusions – My results suggested in hot arid urban landscapes water is a limiting factor for bats, even in urban landscapes where the availability of water may be greater than in outlying native desert habitat. Golf courses had the highest species richness, and included the detection of the uncommon pocketed free-tailed bat (Nyctinomops femorosaccus). Water cover types had the second highest species richness. Golf courses may serve as important stop-overs or refuges for rare or elusive bats. Urban waterways and golf courses are novel urban cover types that can serve as compliments to urban preserves, and other green spaces for bat conservation.
ContributorsBazelman, Tracy C (Author) / Wu, Jianguo (Thesis advisor) / Chambers, Carol L. (Thesis advisor) / Smith, Andrew T. (Committee member) / Arizona State University (Publisher)
Created2016