Browsing by Subject "Predator-prey"

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    Spatial and temporal variability in zooplankton-fish interactions in freshwater communities.
    (2011-06) Holbrook, Beth Victoria
    Abiotic and biotic factors interact at multiple scales to create heterogeneity in the distribution of zooplankton and zooplanktivorous fish in the pelagic area of freshwater lakes. In this dissertation, I explored the predator-prey relationship between these trophic levels in four studies conducted at a variety of spatial and temporal scales. The objective was to identify the processes that may structure spatial heterogeneity in these populations. At the smallest scales in the laboratory, I simulated light and temperature conditions similar to those found in an oligotrophic lake and observed interactions between age-0 lake trout (Salvelinus namaycush) and mysids (Mysis diluviana), and determined that the intake rate of age-0 lake trout (mg min-1) could be modeled as a function of mysid biomass (mg m-2). I then applied this model to field data collected at intermediate scales at a spawning shoal in Lake Superior and determined that age-0 lake trout distributed in a spatially predictable pattern based on maximizing their growth rate potential. I also explored the more general relationship between pelagic zooplankton biomass and fish density at intermediate spatial scales in three north temperate lakes. In all six depth strata that I analyzed, there was consistent and significant autocorrelation in the distribution of zooplankton biomass, but spatial structure in the distribution of fish density was weaker and more variable. I also detected a significant bottom-up influence of zooplankton biomass on the spatial structure of fish density in three of the six depth strata that I analyzed, but I did not detect any top-down influences of fish density on the spatial structure of zooplankton biomass. Finally, I explored the influence of surface temperature and mesoscale eddies on the distribution of epilimnetic zooplankton biomass and fish density at large scales in Lake Superior. Circulation patterns associated with prevailing wind conditions could explain some of the spatial patterns in zooplankton biomass, but epilimnetic fish distributions showed no pattern during both years of the study.
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    Survival In A Landscape Of Fear: Prey Behavioral Responses To Predation Risk That Varies In Time And Space
    (2018-03) Palmer, Meredith
    The fear of predation is a driving force shaping prey behavior and ecology. The “landscape of fear” hypothesis posits that prey perceive their environment in terms of peaks and valleys of predation risk; the behavioral decisions prey make as they navigate this “landscape” reflect a fitness tradeoff between minimizing risk and obtaining sufficient resources. While landscapes of fear have been well-examined in small-scale experimental systems, logistical challenges have greatly prohibited their study in communities of large vertebrates which inhabit vast spatial expanses. In a novel investigation of an unparalleled long-term camera trap dataset, I examined the behavioral tactics used by guilds of mammalian herbivores to navigate a risk-resource tradeoff in a natural savanna ecosystem. By studying the choice and scale of anti-predator behaviors elicited in response to multidimensional predation risk from an apex predator, the African lion (Panthera leo), I sought to derive overarching mechanisms which structure communities across different spatial and temporal scales. First, I determined the spatial mechanisms structuring the landscape of fear by quantifying anti-predator behaviors elicited in response to different components of the predation process (i.e., the risk of encountering predators vs. the risk of being killed given an encounter). I then incorporated predictable temporal variations in predation threat, assessing whether prey perceive heterogeneity in risk across time as well as space. For this, I tested whether prey changed their behaviors in response to diel fluctuations in lion activity patterns or monthly nocturnal variation in lion hunting success driven by changes in night-time luminosity. Finally, I evaluated immediate responses to cues of imminent predation risk within herbivore communities. I characterized the types of anti-predator behaviors used to mitigate risk across each spatiotemporal scale and examined how choice of anti-predator behavior changed across resource gradients in order to understand the costs and benefits associated with different suites of behavioral decisions. My work suggests that prey minimize dynamic variation in predation risk by exhibiting a variety of complementary and compensatory behaviors across spatiotemporal scales. This type of complexity is frequently suggested but rarely tested, and directly informs our ability to predict predator-mediated impacts on community structure and ecosystem functioning.