Nesting success is an important vital rate affecting the reproductive fitness of birds, and predation typically is the single most important factor affecting nesting success. Presumably, birds should nest in locations that maximize nest survival. If specific nest characteristics increase the probability that a nest will hatch, natural (phenotypic) selection could favour use of sites with these features, producing nonrandom patterns of nest site use. Alternatively, birds that are highly selective in nest site choices might be at a disadvantage if predators learn to forage preferentially in these locations and improve their efficiency in depredating nests; in this case, random nesting patterns could be favoured. Finally, it has been hypothesized that predation pressure can influence nest site selection patterns of entire bird communities. If predators develop a search image to hunt for bird nests, then nests that are most similar to each other, irrespective of species, should sustain higher mortality. To evaluate these hypotheses, I quantified nest site selection patterns of multiple species of ground-nesting dabbling ducks in areas where predation pressure was normally high, and compared these patterns to those on areas where predation was relaxed. Predation pressure was experimentally reduced by removing common predators of duck nests and females (mainly red foxes, coyotes, skunks and raccoons) on some study areas and not on others (controls). Predator removal and natural causes produced a 10-fold difference in duck nesting across study sites, allowing for investigation of effects of predation pressure on nest site selection of ducks. Coarse scale habitat selection patterns were similar to results reported in previous studies; blue-winged teal and northern shoveler were found more often in native grassland than in other habitat types, while gadwall and mallard nests occurred more frequently in shrub patches when compared with other habitat patches. A difference in nest site characteristics was observed between hatched and depredated nests for gadwall and northern shoveler but not for blue-winged teal and mallard. However, in all species, the nest site selection patterns were non-random. Thus, the process of nest predation did not shape patterns of nest site choice. Contrary to predictions, inter-specific overlap in nest site features was not related to predation pressure: nests that overlapped most with features of other species did not suffer higher predation, nor did inter-specific overlap in nest characteristics decrease during the nesting season. These findings were inconsistent with the hypothesis that community-level patterns of nest site use are differentiated as a result of predation pressure. Long-term work on nest site use by individually marked females of numerous ground-nesting bird species would be informative, as would experimental studies of other hypotheses about factors affecting nest site choices in birds.

Determining the relative roles of top-down vs. bottom-up forces in controlling the structure of ecological communities is of primary importance because anthropogenic nutrient loading, overharvesting of consumers, and potential interactions of these forces are pervasively changing ecosystems throughout the world. Here I use both field experimentation and meta-analyses to investigate the role of predators in controlling community composition, the relative roles of herbivores vs. nutrient enrichment in controlling the abundance of benthic primary producers, and the influence of herbivore diversity on the community structure of coral reefs. On a coral reef in the Florida Keys, I showed that release from predation by large fishes and invertebrates via exclusion cages allowed population increases in the gorgonian-eating gastropod Cyphoma gibbosum which increased predation rates on gorgonian corals. To directly address the relative roles of top-down and bottom-up forces in controlling primary producers in benthic marine habitats, I used factorial meta-analysis of 54 field experiments that orthogonally manipulated herbivore pressure and nutrient loading to quantify the effects of consumers and nutrient enrichment on community structure. The relative effects of herbivores vs. nutrient enrichment were context dependant, varying with latitude, the type of primary producer, and the nutrient status of the system. To address the influence of herbivore diversity on the community structure of Caribbean coral reefs, I used manipulative field experiments over two years to show that a Caribbean reef changes dramatically as a function of herbivorous fish diversity. The effects of herbivore diversity on community structure were strong in both years of the experiment due to different diet preferences among herbivores. Higher herbivore diversity suppressed macroalgal abundance, increased abundance of crustose coralline algae, reduced coral mortality, and increased coral growth when compared to treatments with lower herbivore diversity. Complementary feeding by different fishes drove these patterns because macroalgae were unable to effectively deter feeding by fishes with different attack strategies. Thus, herbivore diversity appears to play an important role in the healthy function of coral reef ecosystems via complementary feeding of different herbivore species.

I developed a spatially explicit individual-based model (IBM) to capture the dynamic behavioral interaction between a fierce predator (killer whale, Orcinus orca) and a clever prey (dusky dolphin, Lagenorhynchus obscurus), and to answer the ultimate question of costs vs. benefits for dusky dolphins when making anti-predator decisions. Specifically, I was interested in calculating time/distance budgets for dusky dolphins in the presence/absence of killer whales and the presence/absence of movement and behavioral rules, which presumably evolved in response to spatial and temporal variations in predation risk. Results reveal that dusky dolphins rest less, travel more and have reduced foraging time when killer whales are present. These effects are more pronounced with increased presence of killer whales. The model suggests that a strong reason favoring the adoption of short and long-term anti-predator mechanisms is increased survival resulting from decreased encounters with killer whales. Further, a mother with calf rests less and travels more when killer whales are present relative to a dolphin without calf. However, a mother with calf on average, flee shorter distances and have fewer encounters with killer whales than a dolphin without calf. Thus, despite ecological costs, it makes evolutionary sense for dusky dolphins to adopt anti-predator rules. Bioenergetic consequences for dusky dolphins with and without calf were estimated as total energetic costs and foraging calories lost due to low/high presence of killer whales. I calculated total energy costs as: Foraging costs (FC) Locomotor costs (LC) (Travel) or LC (Travel) LC (Flee) based on the absence, as well as low/high presence of killer whales. Foraging costs contributed significantly to total energetic costs estimated. Travel costs are minimal owing to proximity to deep waters. The total energy costs were not significantly higher from low or high presence of killer whales for mother with calf, but increases by about 90 kcal/day for a dusky without calf. However, I estimate foraging calories lost due to increased killer whale presence is almost 5 times more for mother with calf. Therefore, it might be important to consider indirect predation risk effects by social type in future studies on animal bioenergetics.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2000. / Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 110-119). Also available on the World Wide Web.

Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 16, 2010). Includes bibliographical references. Also issued in print.

Thesis (Ph.D)--Biology, Georgia Institute of Technology, 2009. / Committee Chair: McCarty, Nael A.; Committee Co-Chair: Kubanek, Julia; Committee Member: Derby, Charles; Committee Member: Goodisman, Michael; Committee Member: Pardue, Machelle; Committee Member: Weissburg, Marc. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M.S.)--University of North Carolina at Wilmington, 2003. / Vita. Includes bibliographical references (leaves : [48]-52).

The presence of agrochemical residues in both urban and agricultural water bodies has become ubiquitous, often producing deleterious effects in the impacted watershed including reductions in biodiversity, alterations in species interactions, and toxicity to non-target organisms. While these effects have been studied on metazoan consumers, the consequences of agrochemical contamination on microorganisms, such as bacteria, protozoa, and viruses, are poorly understood. Agrochemicals could act directly on microorganisms, including pathogens, by either facilitating their survival or decreasing their abundance. Further, a multitude of indirect effects of agrochemicals on microorganisms are possible, whereby agrochemicals alter predation, competition, or parasitism on or available nutrient to microbes. The primary method by which agrochemicals enter water bodies is through stormwater and agricultural runoff, which can also introduce agriculturally-associated zoonotic pathogens. Presently, regulatory standards utilize fecal indicator bacteria (FIB) to predict the presence of pathogens in contaminated watersheds. However, if agrochemicals have different effects on FIB and bacterial pathogens, then these regulatory standards might be confounded by the presence of pesticide residues in impacted water bodies. Additionally, if agrochemicals promote the survival of zoonotic pathogens, then the presence of pesticide residues could potentially increase risks to human health. The studies in this dissertation investigated both the direct and indirect effects of agrochemicals on the growth and survival of FIBs ( Escherichia coli and Enterococcus faecalis), zoonotic bacterial pathogens (E. coli O157:H7, and Salmonella enterica), and two virus groups (human polyomaviruses and adenoviruses). The agrochemicals utilized in these experiments are among the most prominently used in their respective pesticide classes and included the herbicide atrazine, the insecticide malathion, the fungicide chlorothalonil and inorganic fertilizer containing phosphate and fixed nitrogen. Initially, complex mesocosms containing zooplankton, phytoplankton, leaf litter, and vertebrate and invertebrate species were used to examine net (direct and indirect) effects of agrochemicals on FIB in sediments. Subsequent studies utilized experiments in simplified microcosms to detect direct or indirect effects (i.e., predation, competition or effects on nutrient resources) on FIBs and pathogens. In complex mesocosms, atrazine and fertilizer significantly increased FIB densities in the sediment; however, because of the complexity of the mesocosms, it was not possible to determine whether these results were the product of direct or indirect agrochemical effects. Simplified microcosms, limited to predominantly direct effects, as well as in vitro growth curves, revealed no direct effects of any agrochemical treatment on either growth or survival of FIB or bacterial pathogens. When algal communities were allowed to establish, however, atrazine significantly reduced both phytoplankton and E. coli densities in the water column, but increased E. coli densities within the sediments. These effects on E. coli were indirect because they required the presence of algal species. To investigate indirect effects of predation on FIBs and E. coli O157:H7, we manipulated the presence and absence of an obligate heterotroph, Tetrahymena pyriformis, a facultative heterotroph, Ochromonas danica, and natural protozoan populations. In both laboratory and greenhouse microcosm experiments, the fungicide chlorothalonil significantly reduced all protozoan populations, which resulted in increased densities of FIBs and E. coli O157:H7 because of reduced predation. Atrazine was not found to have any significant direct effect on the densities of T. pyriformis or natural protozoans; however, atrazine did significantly reduce O. danica densities in greenhouse experiments. In laboratory experiments with O. danica, atrazine treatments resulted in decreased densities of E. coli O157:H7. Presumably, atrazine prevented or reduced photosynthesis forcing O. danica to increase its predation on E. coli thus shifting its trophic level. These studies reveal that agrochemicals can have a significant effect on microbial communities, but that these effects are often indirect and mediated through alterations of nutrient resources and predation. Atrazine application reduced FIB and pathogen densities in the water column via reduction of phytoplankton and increased predation by O. danica. These data suggest that the net effects of atrazine is deleterious to FIB survival in the water column and that application of this herbicide could result in an ecosystem service, reducing the abundance of zoonotic pathogens and lessening the risk to human health. However, elevation of FIB densities was observed in the sediments when atrazine was applied. The potential resuspension of increased sediment bacteria may negate or out-weigh the deleterious effects of atrazine on bacteria in the water column. Chlorothalonil application decreased protozoan densities, lessening the stress of predation on the bacterial targets and increasing FIB and E. coli O157:H7 densities. The use of chlorothalonil may therefore have negative implications for human health risks, as the reduction in predation seems to facilitate the survival of zoonotic waterborne pathogens. Understanding the net effects of agrochemicals is important for public health, as pesticide applications can act to either maintain or diminish potential bacterial and protozoan pathogens of humans. These studies show that indirect effects of agrochemicals on non-target microbes tend to be more prominent than direct effects and can significantly impact the fate of bacterial pathogens in aquatic environments.

I studied the insect seed predator community on mesquite plants (Prosopis spp.) to investigate patterns of community composition in space and time, attempting to better understand the factors that led to the coexistence of many seed predator species on a single plant. This dissertation begins by testing the controversial species limits of Prosopis section Algarobía because hosts may act as environmental filters to insect seed predators. I found evidence for at least eight North American Prosopis species (section Algarobía). Second, I describe and add to the known natural history of 113 arthropod species among 315,174 individuals I collected from seedpod samples across the United States and Mexico. These samples included 187 trees from eight North American Prosopis species from section Algarobía and three from section Strombocarpa. Third, I examined reproductive timing in Prosopis and show that neighboring trees of the same species reproduce synchronously, whereas closely related species stagger reproduction. I found that photoperiod is the main cue that initiates flowering, but that multiple cues are involved. Thus, synchronous reproduction may act as an equalizing process that facilitates coexistence of seed predators in this system. Fourth, I tested for evidence of spatial and temporal niche partitioning among Prosopis seed predators. I found that the rank abundance of seed predators varies little over space and time, suggesting that this community exists in a homogeneous competitive environment. I also found that although a few species restrict the use of seeds to particular host plants or developmental stages of the pods, there is little evidence of niche partitioning. Finally, I looked for evidence of competition between seed predators and examined a number of factors that may allow for coexistence of these species. I found no evidence of interspecific competition or facilitation, suggesting that species somehow either avoid competition or that present patterns are the product of past competitive interactions. Natural enemies occur too sporadically to allow for apparent competition and I found no relationship between their occurrence or abundance and those of the seed predator species I studied. I found a positive correlation between rank abundance ability and fecundity, inconsistent with expectations of life-history or competitive-colonization trade-offs. Therefore, the only stabilizing process consistent with patterns found in this system is the niche regeneration hypothesis. I found that one seed predator species lays eggs most often away from both interspecific and intraspecific competitors, a pattern consistent with active avoidance as a second equalizing process within this system.