Browsing by Subject "predation"
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Item Arthropod Predation in Brassica Agroecosystems: Effects of Latitude, Community Composition, and Diet Breadth(2020-04) Gray, HannahArthropod predators provide crucial pest management services by consuming herbivore prey in agroecosystems. Yet, variation in arthropod predation strength among cropping systems and regions can prevent farmers from taking advantage of this alternative pest management strategy. This research examines underexplored potential causes of variation in arthropod predation in agroecosystems. Arthropod predation increases at lower latitudes. However, it is unknown whether this gradient extends to agroecosystems. Diet breadth of an arthropod predator can influence whether a predator can adequately control resident herbivore populations and can impact predation in a community context by determining whether predatory taxa will compete over shared prey, attack each other as intraguild prey, or partition herbivore taxa into distinct prey niches. To assess the effect of latitude, I first compared predation rates on live and artificial sentinel prey in Brassica agroecosystems between the tropical Federal District, Brazil and temperate Minnesota, United States. Contrary to expectations, I found that predation rates on all bait types were similar between the two localities and that reduced predation rates in the Federal District may be related to higher prey densities. Next, to further explore latitudinal effects, I assessed predation rates in Brassica agroecosystems across 15 degrees of latitude in the United States and 21 degrees of latitude in Brazil. Surprisingly, my results revealed a reverse predation gradient whereby arthropod predation increased with latitude in both countries. To examine the role of diet breadth, I first tested methods to improve molecular gut content analysis of arthropod predators by verifying broad metabarcoding results with species-specific melting curve analysis. This study documented common false positive and false negative taxonomic results and suggested that a species-specific verification step is necessary to ensure accurate depictions of arthropod trophic interactions. Lastly, I use the results of the gut content analysis to characterize the diet breadth of three coccinellid predator species (Coleomegilla maculata, Hippodamia convergens, and Harmonia axyridis) collected from a Brassica agroecosystem in Minnesota. I found that both herbivore and intraguild prey consumption were common among coccinellid species, but that C. maculata was least likely to engage in intraguild predation of fellow coccinellids.Item Behavioral ecology of parasitoid diet breadth and insect defenses(2017-07) Stenoien, CarlOne of the primary challenges animals face is consuming enough nutrients of sufficient quality that they might realize their reproductive potential. Many strategies have evolved, but robust explanations for the causes and consequences of variation in diet breadth remain elusive. I’ve used field and comparative lab studies of a specialist parasitoid wasp (Pteromalus cassotis) with a closely-related generalist (Pteromalus puparum) across several potential butterfly host species to better understand how physiological and behavioral trade-offs might limit parasitoids' host ranges. When paired with eleven host species, both parasitoids preferred those hosts on which they performed best, but I found little support for the idea that physiological trade-offs drive the evolution of specialized foraging strategies. Intriguingly, the generalist was more likely than the specialist to accept unsuitable hosts, while the specialist was more likely than the generalist to reject suitable hosts. I also reared monarch butterflies (Danaus plexippus) to be more or less chemically defended and found that host toxicity influenced the behavior and performance of the specialist. The generalist often killed monarch hosts, but was incapable of developing in them. Finally, I investigated the role of behavior in avoiding natural enemy-induced mortality of insect pupae, which are relatively immobile and are often presumed to be vulnerable to natural enemies. I review many examples to show that pupae likely benefit from a variety of behaviors performed before pupation (by the larva or pre-pupa), behaviors of the pupa itself, and behaviors of conspecific and heterospecific individuals. Taken together, my dissertation provides the first details on the natural history and chemical ecology of interactions between P. cassotis and the monarch butterfly. My findings suggest that, in some cases, behavioral decisions may be more important than physiological trade-offs in shaping animal diet breadth. These findings have implications for organisms in rapidly changing environments and biological control efforts because they demonstrate that specialist foragers may retain the evolutionary potential for host switches, and generalists can cause difficult-to-measure non-target mortality.Item Data, R Code, and Output Supporting "An Historical Overview and Update of Wolf-Moose Interactions in Northeastern Minnesota"(2017-10-06) Fieberg, John R; Mech, L. David; Barber-Meyer, Shannon; jfieberg@umn.edu; Fieberg, John RThese files contain data and R code (along with associated output from running the code) supporting all results reported in, "Mech, L. D., J. Fieberg, and S. Barber-Meyer. In press. An historical overview and update of wolf-moose interactions in Northeastern Minnesota. Wildlife Society Bulletin." In this paper, we explored relationships between wolf numbers, monitored in part of the Minnesota moose range, and moose calf:population and estimated log annual growth rates of moose in Northeast Minnesota.Item Wolf-Beaver Dynamics in a Southern Boreal Ecosystem(2021-04) Gable, ThomasPredator-prey relationships can have wide-ranging ecological and landscape-level effects. Knowledge of these relationships is therefore crucial for understanding how changes in predator-prey communities affect ecosystems. Throughout much of the circumpolar boreal ecosystem, wolves are significant predators of beavers and beavers important prey for wolves, yet wolf-beaver dynamics remain poorly understood. My objective was to shed light on this predator-prey dynamic by studying wolf-beaver interactions in the Greater Voyageurs Ecosystem (GVE), a southern boreal ecosystem in Northern Minnesota. Specifically, I wanted to understand where and how wolves hunt beavers, what impact wolf predation has on beaver populations, and how wolf predation on beavers might impact ecosystem function. By searching 11,817 GPS-clusters from 24 GPS-collared wolves during 2015-2019, I documented 748 instances where wolves attempted to ambush beavers and 214 instances where wolves killed beavers. Through this, I determined wolves are able to ambush beavers by anticipating the movements and behavior of beavers due to a fundamental understanding of beavers’ sensory abilities. Further, wolves can strategically select ambushing locations by simultaneously accounting for abiotic and biotic factors, ultimately allowing wolves to counter beaver’s defenses and exploit this unique prey. The extent to which wolves influence beaver population change has been debated for decades despite a complete lack of quantitative data on the subject. I estimated, by determining kill and predation rates, that wolf packs can remove 38-42% of the beaver population in their territory in a year. Yet, in high-density beaver populations such as the GVE, predation pressure appears to have little influence on beaver population dynamics because beaver populations can quickly compensate for predation. Though wolves may not alter beaver population size, I demonstrate how wolves alter wetland creation and recolonization by killing dispersing beavers. By studying beaver pond creation and recolonization patterns, I determined that 84% of newly created and recolonized beaver ponds in the GVE remained occupied until the fall, whereas 0% remained active after a wolf killed the dispersing beaver that colonized that pond. By affecting where and when beavers engineer ecosystems, wolves alter all of the ecological processes that occur due to beaver-created impoundments.