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Seascape ecology provides a useful framework from which to understand the processes governing spatial variability in ecological patterns. Seascape context, or the composition and pattern of habitat surrounding a focal patch, has the potential to impact resource availability, predator-prey interactions, and connectivity with other habitats. For my dissertation research, I combined a variety of approaches to examine how habitat quality for fishes is influenced by a diverse range of seascape factors in sub-tropical, back-reef ecosystems. In the first part of my dissertation, I examined how seascape context can affect reef fish communities on an experimental array of artificial reefs created in various seascape contexts in Abaco, Bahamas. I found that the amount of seagrass at large spatial scales was an important predictor of community assembly on these reefs. Additionally, seascape context had differing effects on various aspects of habitat quality for the most common reef species, White grunt Haemulon plumierii. The amount of seagrass at large spatial scales had positive effects on fish abundance and secondary production, but not on metrics of condition and growth. The second part of my dissertation focused on how foraging conditions for fish varied across a linear seascape gradient in the Loxahatchee River estuary in Florida, USA. Gray snapper, Lutjanus griseus, traded food quality for quantity along this estuarine gradient, maintaining similar growth rates and condition among sites. Additional work focused on identifying major energy flow pathways to two consumers in oyster-reef food webs in the Loxahatchee. Algal and microphytobenthos resource pools supported most of the production to these consumers, and body size for one of the consumers mediated food web linkages with surrounding mangrove habitats. All of these studies examined a different facet of the importance of seascape context in governing ecological processes occurring in focal habitats and underscore the role of connectivity among habitats in back-reef systems. The results suggest that management approaches consider the surrounding seascape when prioritizing areas for conservation or attempting to understand the impacts of seascape change on focal habitat patches. For this reason, spatially-based management approaches are recommended to most effectively manage back-reef systems.

Large carnivores play many vital biological, economic, and conservation roles, however, their biological traits (low population densities, cryptic behavior) make them difficult to monitor. Pumas have been particularly difficult to study because the lack of distinctive markings on their coats prevents individual identification, precluding mark-recapture and other similar analyses. Further, compared to temperate areas, research on the interspecific interactions of Central American felids is particularly lacking. I used single- and multi-season, single-species occupancy models and two-species co-occurrence models to analyze camera trapping and habitat data collected at eight study sites across Belize. Puma occupancy was positively influenced by jaguar trap success, understory density, canopy cover, and human trap success, and negatively influenced by stream density. Jaguar trap success was the best predictor of where pumas occurred, while prey species were not found to influence puma occupancy. Mean occupancy was 0.740 (0.013) and ranged from 0.587 (0.042) to 0.924 (0.030). Over time, puma occupancy rates were generally high (> 0.90) and stable. Puma occupancy was higher in logged areas, suggesting that current levels of natural resource extraction at those sites were not detrimental to the species. Co-occurrence modeling showed little evidence for interactions between the carnivores, suggesting that jaguars may be acting as an umbrella species and that conservation efforts directed at jaguars are likely to benefit the other carnivores, including pumas. Overall, these findings are positive for puma conservation, but human-induced land use change is expanding and further monitoring will give us insight into how pumas respond to human encroachment. / Master of Science

Bacteria are ubiquitous in all ecosystems and are often challenged by multiple stresses such as extreme temperatures, high salt concentrations, nutrient limitation, pH variations, radiation, predation and the presence of antibiotics/toxins. The most challenging among them is predation pressure which is one of the major causes of their mortality in different niches. Bacteria have evolved different adaptive measures to counter predation. Some of them include change in shape, size, motility, and unpalatable aggregate formation. Aromatic β-glucosides such as salicin, produced by plants as secondary metabolites, play a significant role in protecting them from herbivores. Members of the family Enterobaceriaceae primarily present in soil, e.g. Erwinia chrysanthemi (a phytopathogen) and Klebsiella aerogenes, can utilize the aromatic β-glucosides salicin and arbutin (likely to be present in soil derived from decomposing plant materials) as a carbon source unlike their fellow members such as Escherichia coli, Shigella sonnei, and Salmonella present in the gut environment. Bacteria can obtain energy by metabolizing β-glucosides in the form of glucose. Whether they can also use these molecules as defense tools in a manner similar to plants is an intriguing possibility. In such an event, Bgl+ bacteria could derive a dual advantage in terms of energy generation and protection from predation. The current study was initiated to investigate a possible link between β-glucoside metabolism and self-defense in Enterobacteriaceae. Different members of Enterobacteriaceae comprising of both laboratory strains and natural isolates were considered as prey. Predators included were laboratory strains and soil isolates of bacteriovorous nematodes of the Rhabditidae family, the amoeba Dictyostelium discoidium and a bacteriovorous Streptomyces sp. The predator-prey interaction was analyzed by performing viability and behavioral assays in the context of β-glucoside metabolism Results presented in Chapter 2 show that active catabolism of aromatic β¬glucosides like salicin, arbutin and esculin by Bgl+ bacteria decreases the viability of their predators. The aglycone products released during β-glucosides metabolism, e.g. saligenin in the case of salicin, are the causative agents of the mortality of the predators. The lethality is reversible up to a specific threshold of exposure. Saligenin acts as a chemo-attractant that lures and kills Caenorhabditis elegans N2. In the case of nematodes that succumb, bacteria can derive nutrition from the dead predators indicating a conversion of prey to predator. Experiments with mutant strains of Caenorhabditis elegans suggest that the dopaminergic receptor dop-1 is involved in mediating saligenin toxicity. Studies mentioned in Chapter 3 revolve around the relevance of the predator-prey interaction discussed in Chapter 2 in the natural environment. Members of Enterobacteriaceae and their predator amoebae (cellular slime molds) and nematodes were isolated from soil. They show coexistence in most of the soil samples analyzed. All the predators isolated from soil and other natural isolates of Caenorhabditis succumb to saligenin as their laboratory counterparts with higher sensitivity in some of the strains. Soil nematodes belonging to genera Oscheius and Mesorhabditis avoid saligenin unlike the members of Caenorhabditis genus which are attracted towards saligenin. This indicates that the soil nematodes are often exposed to saligenin or saligenin-like compounds, resulting in the evolution of a genetic machinery to avoid these toxic compounds. Studies with quasi-natural environments like soil and fruit indicate that β-glucoside metabolism have similar effects on predator prey interaction in these environments, reinforcing the relevance of these observations to the natural ecology of the organisms. The studies reported in Chapter 2 and 3 shed light on a novel defense strategy of otherwise non-pathogenic members of Enterobacteriaceae which comes with a dual advantage. These results have also brought into focus issues such as the benefit derived by bacterial populations that are genetically heterogeneous, consisting of both Bgl+ and Bgl-strains. The broad implications and future directions of the work are discussed in Chapter 4. Work presented in Appendix deals with the investigation of the pattern of cellobiose utilization in Shigella sonnei. As mentioned in Chapter 1, it is known that members of Enterobacteriaceae exhibit diversity in their pattern of β-glucoside utilization. Wild type strains of both E. coli and Shigella sonnei are unable to utilize Arbutin, Salicin and Cellobiose. While E. coli can acquire cellobiose utilizing ability directly from the wild type state (Arb-Sal-Cel-), Shigella sonnei strains, though closely related to E. coli, have to undergo a series of mutations in a specific sequence to become capable of utilizing these sugars. Characterization of a few Shigella sonnei Cel+ mutants showed a different mode of activation of the chb operon (known to be involved in cellobiose utilization in E. coli). Considering the ecological significance of the ability to hydrolyze aromatic β-glucosides, a detailed understanding of the metabolic capability of different strains and the molecular mechanism involved becomes significant.

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