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Introduced species, like the lady beetle Harmonia axyridis, have been linked to declines of native species through mechanisms including intraguild predation and competitive superiority. However, competitive differentials between species may be mitigated if subdominant species can utilize resources that dominant species cannot. Previous research has shown that some strains of the aphid Aphis craccivora are toxic to H. axyridis. My goal was to investigate use of this resource by both H. axyridis and other lady beetles, to determine whether these aphids might be an exploitable resource for subdominant lady beetle species. I first examined the behavioral responses of adult and larval H. axyridis to toxic strains of A. craccivora. I found that adults invested less time and laid fewer eggs with toxic than nontoxic aphids, and larvae consumed toxic aphids at a slower rate, often refusing them as a food source. I then tested whether six other lady beetle species could use the aphids, monitoring larval development in no-choice environments with different strains of A. craccivora. All species showed increased survival and development rates relative to H. axyridis on toxic aphid strains, suggesting these aphids may allow other coccinellid species to experience competitive release from the otherwise dominant H. axyridis.

Rodent commensal species produce great damage in agriculture and urban areas. As invasive species they can endanger local species and are carriers and vectors of several important zoonoses. Control methods rely mainly on the use of warfarins, which can be inadvertently be taken up by untargeted species. Warfarins have also lost their efficacy in rodents due to the development of genetic resistance. In addition, these methods are considered inhumane as they cause a slow and painful death due to haemorrhages. Olfaction is a main source for environmental risk assessment by rodents, and it can be used to modify their use of space. My aim in this thesis was to identify behavioural reactions of the house mouse (Mus musculus), using laboratory strains as models of wild animals, to ecologically meaningful chemical messages, including predator and plant chemical olfactory cues. My results showed that mice avoided complex ferret olfactory cues and ethanol which is a ubiquitous chemical related to fruit rotting and ripening. The feline protein Fel d 1, which belongs to the secretoglobin family and is a major cat allergen in humans, did not elicit significant avoidance or alter foraging behaviour in mice. However, Trimethylthiazoline purified from fox faeces, elicited clear avoidance behaviour and stress responses. I carried out a bibliographic review to evaluate and discuss rodent pest control methods from an ethical standpoint. This literature showed that many of the current methods of pest control are considered inhumane, and do not tally with current society concerns and welfare standards in other domains such as farms or laboratory animals. These results raise new research questions to identify ferret and plant chemical compounds that can induce rodent avoidance, and to carry out next stage of research with wild animals both under laboratory and field conditions.

O gerenciamento dos estoques pesqueiros, um dos instrumentos da biomanipulação, deve ter início com a classificação das espécies existentes e sua diversidade, a estrutura da rede alimentar e as relações reguladoras, como a relação predador-presa. O lago Paranoá (Brasília - DF) é um reservatório urbano que sofre pressões antrópicas devido a seus usos múltiplos. Após a construção enchimento, sucessivas introduções de espécies ictíicas exóticas causaram um desequilíbrio que, associado às pressões descritas acima, geraram uma aceleração no processo de eutrofização deste ambiente. Desta forma, os objetivos deste trabalho foram: avaliar os impactos ambientais da introdução das espécies predadoras sobre a cadeia trófica e a qualidade da água do reservatório; determinar a eficiência das diferentes espécies de predadores no controle das presas nas áreas marginais da represa, discutindo possíveis estratégias de manejo pesqueiro baseadas na estocagem de peixes predadores. Para tanto foram construídos 10 limnocurrais com lonas impermeáveis numa baía localizada no ETE-Norte (Estação de tratamento de esgotos - Norte). Em seu interior, após a retirada de todos os peixes, foram estocadas por um período de 28 dias, duas espécies de predadores (Cichla ocellaris e Pseudoplatytoma fasciatum) e uma comunidade simplificada de presas (Tilapia rendalli e Oreochromis niloticus), acima da capacidade do suporte do sistema, definida em 4 classes de tamanho. As biomassas de estocagem foram determinadas a partir da aplicação de retenona em uma área com dimensões conhecidas, e extrapoladas para as áreas dos limnocurrais. As variáveis físicas e químicos da água foram acompanhados semanalmente durante o experimento. Não houve diferenças significativas entre os tratamentos, em relação às variáveis limnológicas. Quanto ao controle das presas, o tucunaré mostrou-se um predador eficiente em relação às classes de tamanhos menores ) (2 - 6,9 cm e 7 - 12,9 cm), fato não observado para o tratamento com surubim. De acordo com os resultados obtidos, não foi comprovada a hipótese de cascata trófica devido à complexidade das interações entre os organismos em ambientes tropicais. / The managing of the fish stocks, one of the tools of the biomanipulation, must begin with the classification of the present species and their diversity, of the structure of the food web and of the regulation relations (as the relation predator-prey).The Paranoá Lake (Brasília, DF) is an urban reservoir that suffers human pressures as a result of its multiple uses. After its construction and filling, the successive introduction of many fish exotic species resulted in an unbalance that, associated with the pressures described above, generated an acceleration in the eutrophication process of the ambient. In this way, the objectives of this work were: evaluate the environmental impacts from the introduction of the species predators in food web and quality from the reservoir\'s water; decide the efficiency of the species of predators in the prey\'s control in the marginal areas from dam, discussing possible fishing strategies of management based in the Stocking of fish predators. Them, 10 limnocorrals were built with waterproof canvases in a bay located in ETE-NORTE (sewers handling Station - North). In its interior, after retreat of all fishes, by a period of 28 days, two species of predators were stocked (Cichla ocellaris and Pseudoplatystoma coruscans), and a community simplified of prey (Tilapia rendalli and Oreochromis niloticus), above from the capacity of the system, defined in 4 classes of size. The biomasses of stocking were determined from application of rotenona in an area with known dimensions, and overstepped for the areas of the limnocorrals. The physical-chemists parameters from the water were accompanied weekly during the experiment. It had no significant differences between the handlings, regarding the variables limnological. As regards the control of prey, C. ocellaris showed itself an efficient predator regarding the smallest classes of sizes (2 - 6,9 cm and 7 - 12,9 cm), fact do not observe for the handling with P. coruscans. Agreement with the results obtained, was not verified to hypothesis of trophic cascade due to the complexity of the interactions between the agencies in tropical environments.

Human activity modifies the behaviour of large vertebrates and their acquisition of key resources. Despite the predation risk and competition for similar food resources that humans impose, wildlife consumers must acquire key foods across the landscape. Predation risk can modify foraging behaviour, yet we know little about the potential consequences, especially on large spatial scales. Humans may also affect food availability for wildlife by competing for shared prey, which most current harvest prescriptions fail to recognize. Against this background of threats to consumer-resource interactions, my research employed new conceptual, analytical, and practical approaches to seek not only new generalizable insight but also applied solutions. Addressing these goals, I characterized foraging behaviour by grizzly bears (Ursus arctos horribilis) on a focal prey, Pacific salmon (Oncorhynchus spp.), at multiple spatial scales. I predicted how human activity – both as modifications to landscapes and as salmon harvest – might affect bear-salmon interactions. I co-conceived, designed, and carried out this work through a framework of community engagement, which I crafted in collaboration with Indigenous communities in coastal British Columbia (BC). The framework (Chapter 2) identifies how scientists and communities can engage throughout the research process to work towards shared priorities, despite potential challenges in differences of knowledge systems or capacities. Methodologically, I used ratios of stable carbon (δ13C) and nitrogen (δ15N) isotopes in bear hair to estimate relative contributions of salmon in the annual diet of bears and employed existing data on landscape modification and salmon fisheries (i.e., escapement and catch) to characterize human activity and to measure associated variation in salmon consumption by bears. My first empirical contribution (Chapter 3) characterized spatial patterns of annual salmon consumption by grizzly bears across BC. I found substantial differences in salmon consumption within and among grizzly and black (U. americanus) bears in a large coastal region and across BC. Visualizing variation in consumer-resource interactions could guide conservation and management efforts that seek to protect predator-prey associations and marine subsidies for terrestrial ecosystems. I also investigated potential drivers of salmon consumption by bears in interior and coastal watersheds that varied in disturbance (Chapter 4). I found that human footprint in riparian areas of salmon-bearing watersheds affected bear diets more than the amount of salmon biomass available, showing that human activity can disrupt an otherwise strong predator-prey association. My community-based research occurred at the scale of a single large watershed, where I demonstrated how the Wuikinuxv First Nation might design their salmon management prescriptions according to their cultural values (Chapter 5). Despite a reduced abundance of salmon in the area, I identified harvest options that would trade-off benefits to local people and bears equally. In general, my dissertation research contributes to our understanding of the role humans increasingly play in mediating consumer-resource interactions. I also highlight how scientific research can support the leadership that local management can provide in mitigating human impacts to sustain an iconic predator-prey interaction of ecological, economic, and cultural importance. / Graduate / 2020-04-23

A spatiotemporal system of partial differential equations is implemented for describing a marine predator-prey system of shark and prey fish. The model is developed to account for predator migration and for harvesting of both predator and prey animals. The Finite Difference Method is employed to develop a numerical model to describe the behavior of the system in space over time. The dynamics of the system for different initial conditions for predator and prey populations and harvesting rates of both predators and prey using the numerical scheme. The resulting dynamics of the system from adding a predator sanctuary (an area within which the predator cannot be harvested) are also examined. It is hoped that this paper will illustrate that model behaves as a predator-prey system is expected to behave under the tested conditions. / acase@tulane.edu

The extent to which predators regulate prey populations remains a subject of debate. Yet, when predator control is employed as a management strategy, it is often assumed that predators can and do regulate prey populations. From 2011 through 2015, I monitored the demography and space use of coyotes (Canis latrans) and cougars (Puma concolor) on Monroe Mountain in Fishlake National Forest, Utah as part of a larger collaboration investigating the impacts of coyote aerial control on mule deer (Odocoileus hemionus) neonate survival. My primary objective was to assess the impacts of anthropogenic regulation on the respective populations and identify any cascading effects relevant to mule deer management. To meet this objective, I established a monitoring program for both predators by deploying radio-telemetry collars (VHF and GPS) on each, documented predation events, established surveys for small mammals and lagomorphs to monitor primary prey populations during deer parturition (June – August), and collected data on the location and demographic composition of winter-removed coyotes. I analyzed these data primarily in a community-based, animal movement and resource selection framework permitting the integration of data from multiple sources. When evaluating coyote aerial removal as a management strategy, I identified a spatial dependency in the ability to match removals with indices of deer recruitment as Wildlife Services Operations personnel were primarily limited by terrain and tree cover. Thus, matching treatment with deer fawning was highly variable with only a small number of sites where removals were effective. In addition, I found that coyotes selected for sites with the highest densities of lagomorphs while avoiding areas with a high probability of encountering cougars. Coyotes did not select for mule deer fawning sites, although individual coyotes that occupied resource-poor home ranges were more likely to do so. Cougars strongly selected for mule deer high use areas throughout much of the year, only switching to elk (Cervus elaphus) during the cougar harvest season (i.e., winter). Data from cougar kill site investigations match the observed patterns in cougar space use. My results suggest that predator-prey processes are multi-dimensional and dynamic through time, which likely contribute to the lack of resolution regarding the efficacy of predator control and the regulatory potential of predators in general.

Driving into Yellowstone National Park for the first time is a moving experience. Gazing over the sweeping landscapes, seeing a geyser erupt 80 feet into the air, and having your first ‘wildlife encounter’, whether that be a 2 ton bull bison aggressively wallowing on his dirt mound, snorting and kicking up dust, or watching a pack of 6 wolves move through a valley off in the distance, pausing to howl in search of their companions. Yellowstone staff wishes to manage our park in a way that preserves these remarkable experiences. In order to effectively manage this dynamic ecosystem, it is critical to thoroughly understand how different animal and plant species interact with each other and their environment. Wolves were reintroduced to Yellowstone in 1995-1997 and park researchers and managers are still trying to understand how their presence impacts the ecosystem. In Yellowstone, wolves primarily prey on elk; however, predation on bison has started to increase in recent years. We still know little about how wolves hunt bison and what impacts wolves have had on how bison use their environment. The objective of this study was to better understand the behavioral and ecological interactions of wolves and bison, the most dangerous prey for wolves in North America. Since reintroduction, researchers have collected data on how wolves hunt both elk and bison. I used these data to understand 1) the conditions that allow wolves to capture their most dangerous prey, bison, 2) whether wolves have started preying on bison more often as the bison population increased, and 3) whether wolf reintroduction has limited bison use of Yellowstone’s most extreme high-elevation winter range. Finally, I collaborated with ecologists in Scandinavia to determine how wolf predation was affected by a competitor, the brown bear. My study adds to the current body of work addressing the effects of wolf reintroduction in Yellowstone. This research is unique because it focuses on wolf bison interactions, about which little is known in this system. This research also sheds light on the behavioral relationships at play in a special type of predator-prey interaction: predators that hunt dangerous prey

The loss of large apex predators, and their subsequent reintroduction, has been identified as a substantial driver on the structure and function of ecological communities through behavioral mediated trophic cascades (BMTCs). The reintroduction of wolves (Canis lupus) to Yellowstone National Park (YNP) has served as foundational case study of BMTCs. In our system, it has been suggested that wolves have established a ‘landscape of fear’ in which the primary prey, elk (Cervus elaphus), now avoid risky places, which ultimately led to the recovery of the vegetation community. Although this case is frequently cited as a well-understood example of a landscape of fear, researchers never quantified whether elk avoided risky places, a critical component of the BMTC hypothesis. Thus, I employed numerous quantitative approaches to evaluate the role of wolves and cougars on elk habitat selection in northern Yellowstone. The results from this work suggest that the daily activity schedule of wolves provide a temporally predictable period of risk that allows elk to use risky places during safe times. As such, diel predator activity flattened (i.e., made less risky) the landscape of fear for 16 hours per day, 7 days a week, which permitted elk to forage on deciduous woody plants despite the presence of wolves. Thus, suggests that any trophic cascade in northern Yellowstone is likely driven by the consumptive effects of wolves on elk. In addition, my results suggest that daily activity patterns are an important component of predation risk, and as such, provide a predictable avenue for elk to avoid predators despite residing in an environment spatially saturated with wolves and cougars. Thus, the ability of elk to avoid predators through fine-scale spatial decisions provides support for my findings that the current spatial distribution of prey is largely driven by the consumptive effects of predators on the prey population, rather than a landscape of fear. In combination, these results suggest that the landscape of fear, and more generally, fear effects, may be of less relevance to conservation and management than direct killing within free-living, large landscapes.

Benthic invertebrates play important roles as feeding resources for many organisms in different food webs. Shifts in predation of these organisms can generate cascading effects and potentially lead to the disappearance of one or more species from a site. Cascading effects can bring impacts to organisms who aren’t even directly involved, why studies in this field are important for understanding sudden changes in ecosystems. I examined the predation from fish and waterfowl on benthic invertebrates in the shallow and eutrophic Lake Tåkern in the plains of Östergötland County, southern Sweden. The study was experimental and used exclosures (three types, eight replicates) in the shape of 130-liter cages to examine the composition of invertebrates. It was conducted during early spring, a relatively unexamined period for this kind of study. I found no significant differences in the control treatment compared to any of the other treatments regarding biodiversity. The invertebrate fauna was dominated by a small number of species, with a relatively patchy spread throughout the sediment area. Furthermore, the results indicate that the fish hadn’t had the time to properly activate their predatory habits due to prolonged winter temperatures. The waterfowl were considered too absent during the test period to affect the invertebrate community. Future studies in this area are recommended to work with a greater sampling area, to reduce the influence of extreme values.