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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
521

The Importance of Cover for Juvenile Rainbow Trout in Lentic Systems: Field Observations and an Experimental Study on Predation

Tabor, Roger Allen 01 May 1990 (has links)
Juvenile rainbow trout Oncorhynchus mykiss stocked into mid-elevation reservoirs in Utah are vulnerable to predation from piscivorous fish and birds. I determined how effectively juvenile trout used cover to avoid these predators by (1) direct observations (snorkel transects) of habitat selection in two reservoirs and (2) measurements of survival and growth rates in a pond experiment where adult brown trout Salmo trutta were predators. Observations of juvenile trout were conducted within five weeks of stocking in 1988 and 1989. During the day, juvenile trout were abundant in complex inshore habitats and avoided simple habitats such as sand and gravel. Measurements of gut fullness indicated that juvenile trout fed during the day but not during the night. Large Daphnia comprised more than 95% of the diet of juvenile trout. Because large Daphnia were often higher offshore than inshore in both reservoirs, selection of inshore cover is believed to be primarily a response to reduce predation risk. At night, trout in both reservoirs selected more exposed areas and rested on the bottom. In the pond experiment, the presence of brown trout significantly increased mortality of juvenile trout, decreased their growth rates, and caused them to avoid offshore areas. The presence of cover significantly decreased predation rates but did not affect growth of the juvenile trout.
522

Sex-Biased Predation on Taricha by a Novel Predator in Annadel State Park

Brouillette, Amber Noelle 01 December 2008 (has links)
Newts of the genus Taricha have long been studied due to the powerful neurotoxin found in their skin. Tetrodotoxin (TTX) acts by blocking receptors in sodium channels, ultimately resulting in death via asphyxiation. The only documented predators of species in this genus have been snakes of the genus Thamnophis. Recently, predation on Taricha in Ledson Marsh in Annadel State Park, Santa Rosa, CA was discovered. Predation was in the form of laceration or evisceration, and tracking of predation from 1998-2008 showed that it was male-biased. Two species of Taricha were found living sympatrically at this location, the California newt (T. torosa) and the rough-skinned newt (T. granulosa). Fluorometric High Phase Liquid Chromatography (HPLC) analysis was used in order to quantify TTX levels in the skin of ten male and ten female newts of each species. Quantification of TTX was done to determine the influence, if any, that TTX levels may have on sex-biased predation in this population. I predicted that levels of TTX would be greater in females than males, and greater in T. granulosa than T. torosa since very few T. granulosa were preyed upon during the study period. My results indicated that there were significant differences between the sexes, and T. torosa were significantly more toxic than T. granulosa. An in-depth ecological study of relative abundances of both species and identification of the predator are needed at this site to obtain a clear picture of the predator-prey dynamics at Ledson Marsh
523

Cougar Predation Behavior in North-Central Utah

Mitchell, Dustin L. 01 May 2013 (has links)
Cougar (Puma concolor) predation has been identified as being one of several factors contributing to the decline of mule deer (Odocoileus hemionus) throughout the Western United States. In order to better understand how these elusive felines utilize their surroundings and prey, I examined and analyzed cougar predation behavior in North-Central Utah, using global positioning systems (GPS) data from 2002-2010. Twenty-three cougars were fitted with GPS collars and monitored for prey caching behavior. In total 775 potential cache sites were visited and 546 prey remains found. Mule deer comprised the majority of prey at cougar cache sites, but 11 other species were also found. Collectively, adult female mule deer were killed more than any other demographic class. Proportionally there was no difference in the sex or age class of deer killed by cougars in three different population segments, but seasonal differences were found in the number of kills made between cougar groups. Female cougars with kittens had a higher predation rate than males or solitary females, and seasonally more kills were made in the winter vs. summer. Cougars spent an average of 3.3 days on deer kills, and 6.2 days on elk kills. Habitat analyses suggested that cougars preferentially used Gambel oak (Quercus gambelii) over other land cover types when caching prey, as well as selected unburned over burned areas for caching and foraging on prey. These results suggest that cougars utilize dense stands of vegetation cover when stalking and concealing their prey. Wildlife managers may want to consider the use of prescribed burns in areas of high cougar predation on mule deer. This habitat manipulation tool could simultaneously help mule deer populations by reducing the percent of stalking cover afforded to cougars when attempting to kill prey, along with increasing nutrient levels of newly burned foliage and allow for an increased diversity in forb and shrub species available to mule deer.
524

Social animals detecting danger: how social relations influence antipredator behavior in a noisy forest

Fuong, Holly January 2021 (has links)
The risk of death by predation has been a major driver of group living in many prey animals. Animals must adapt to temporal and spatial variation in predation risk and would benefit from using relevant and reliable sources of information both from conspecifics and heterospecifics to better learn about danger. Research on the effects of group living on antipredator strategy has focused largely on group size. However, sociality is often more complex than simple amalgamations of individuals. Those living in groups are likely exposed to unequal levels of predation risk; some are exposed to more danger than others because of factors related to their age, sex, and spatial or social positioning. An individual’s antipredator strategy should reflect its perceived safety levels. I studied antipredator strategies in blue monkeys (Cercopithecus mitis stuhlmanni) in the Kakamega Forest, Kenya. Blue monkeys are arboreal guenons that live in matrilineally-based social groups and form differentiated social relationships. These social relationships could affect how monkeys respond to variable predation risk. Blue monkeys live in dense, biodiverse rain forests and are preyed upon by both aerial and terrestrial predators. They have a well-developed acoustic communication repertoire and have been known to associate with other primates to reduce predation risk (Cords 1987). I conducted five playback experiments and two sets of observational studies, and used data gathered on social interactions among adult females to further our understanding of how group living affects antipredator strategies. I also used 14 years of social interaction data to explore the heritability of social tendencies. In the first chapter, I present a comprehensive literature review of the connections between group living and antipredator behavior. I describe the effects of group size on antipredator behavior and how research on sociality has shifted towards focusing on individuals’ specific relationships and social connectivity. I then describe several ways in which social connectivity has been shown to influence antipredator behavior. I conclude with future directions and then introduce the dissertation. In the second chapter, I focus on heterospecific eavesdropping. I identified the extent to which blue monkey adult females respond to playbacks of alarm and social calls of two syntopic non-predatory bird species—black-faced rufous warblers (Bathmocercus rufus) and joyful greenbuls (Chlorocichla laetissima). Blue monkeys responded differentially depending on both call type and species. I then evaluated differential responses to conspecific and heterospecific callers, hypothesizing that conspecific signals would trigger stronger anti-predator responses because conspecifics are more relevant signals of risk. I conducted a playback experiment in which adult females were presented simultaneously with one alarm or social call from both conspecifics and warblers (4 combinations of alarm and social calls), or ambient rain forest sound (control). Subjects did not differentiate their responses to simultaneous calls according to the type of playback stimulus. These findings suggest that blue monkeys do not differentiate their responses to alarm calls according to caller relevance. Heterogeneous results among different response variables also highlight the importance of examining multiple modes of antipredator behavior. Next, I examine how an individual’s social connectivity influences its antipredator strategy, hypothesizing that more socially connected individuals would benefit from the proximity of more and closely bonded groupmates in enhancing predator avoidance. In Chapter 3, I evaluate the effects of social connectivity on acute antipredator responses, antipredator vigilance, and responses to signals related to various levels of predator-related threat. I first assessed how social connectivity affects the rate at which adult females exhibit acute antipredator responses (such as diving down in trees, climbing up trees, or alarm calling) and the proportion of responses that are major (lasting >30 s), statistically controlling for age, the presence of an infant, and 2-month “seasons”. I predicted that more socially connected individuals would exhibit less frequent acute antipredator responses because they would be better-informed about risk and therefore would exhibit fewer false alarms. I For the same reasons, I also predicted that they would exhibit more major (vs. minor) responses because false alarms are more likely to involve shorter responses (Cords 1987). Contrary to predictions, however, more closely connected individuals exhibited higher rates of acute antipredator responses, which might reflect their enhanced ability to learn about danger from surrounding groupmates, allowing them to detect more potential threats. There was no evidence that social connectivity was associated with the proportion of responses that lasted >30 s. I also found that the rate of acute antipredator responses and the proportion of responses that lasted >30 s varied with season. I then conducted 90-s focal vigilance follows, to assess how long females exhibit antipredator vigilance after controlling for other social and microhabitat factors (e.g., surrounding vegetation density), which can influence conspecific monitoring and exposure to potential predators. I predicted that more well-connected individuals would exhibit lower levels of antipredator vigilance in the absence of any imminent threats and after controlling for other social and spatial factors. More closely connected individuals who were in the spatial center of their social group did spend less time vigilant, but social connectivity was not associated with vigilance times when subjects were at the group’s edge, where exposure to predators and thus predation risk should be highest and antipredator vigilance should generally be higher. In the spatial center of the group, more closely connected individuals should be in a better position to observe their social partners’ antipredator behavior. Microhabitat also influenced antipredator vigilance in multiple ways, which highlights the spatial variation of perceived predation risk in a complex environment. Lastly, I conducted a playback experiment where I examined responses to signals from conspecifics and heterospecifics that are associated with different levels of threat. I predicted that more poorly connected individuals would respond strongly to all signals that might be associated with predators because they must identify personally whether danger is real, whereas more well-connected individuals would have more differentiated responses because they should be near social partners more frequently and can rely on their partners’ antipredator reactions to assess risk levels. However, although subjects did respond more to direct cues of the predator’s presence (its own calls) than to indirect cues of its presence (alarm calls by conspecifics and heterospecifics), there was no evidence that social connectivity affected responses to playbacks. As expected, stimulus type did affect responses—calls from predators (vs. alarm calls or social calls from non-predators) elicited increased looking responses from subjects, which suggests that stimuli that directly signal predator presence will elicit antipredator behavior regardless of the listener’s social connectivity. Overall, social connectivity seems to play a limited role in blue monkeys’ antipredator strategy but there was some evidence that more well-connected individuals were less vigilant when surrounded by groupmates. The ability to distinguish alarm calls by individual callers has not been well-studied, but animals might benefit from making such distinctions if callers vary in how reliably they signal danger. For decades, researchers have tested whether animals can discriminate callers using the habituation-dishabituation paradigm. After habituating subjects by repeatedly presenting calls of one individual, A, they examine whether subjects dishabituate when they hear the calls of a different individual, B (test stimulus). In Chapter 4, I first review studies that used this paradigm to evaluate whether animals discriminate between conspecific callers and then report on two playback experiments which tested whether wild blue monkeys are capable of such discrimination. My review revealed much methodological variation, particularly in the habituation phase and criteria, statistical analysis, and controls. In experiments, I contrasted two methods of habituation, either presenting a fixed number of stimuli (set after pilot observations) or evaluating responses during the series before progressing to the test. Afterwards, I conducted Wilcoxon signed-rank tests to assess habituation statistically. In the first experiment where I played back a fixed number and rate of calls, it was statistically unclear whether subjects habituated to caller A, despite preliminary observations and similar studies that suggested that the experimental design would be appropriate. Because there was not strong evidence that subjects habituated, I did not evaluate statistically whether subjects differentiated between callers in the full dataset. However, in the second experiment where I assessed habituation during the trial, subjects did habituate to caller A and there was weak support that they dishabituated to caller B, which suggests that caller discrimination may occur. From my experiences, I propose an improved design for studies using the habituation-dishabituation paradigm. Lastly, I explore the mechanisms that drive phenotypic variation in social tendencies (and in turn, social connectivity) in adult females. For natural selection to occur, there must be variation in traits, differentiated fitness benefits based on phenotypes, and heredity or a genetic basis underlying phenotypic variation. The previous chapters highlight the variation in and some of the benefits of social connectivity. In Chapter 5, I conducted an exploratory analysis to examine what factors account for phenotypic variance. Using animal models, I found that both environmental and additive genetic variance accounted for some of the phenotypic variance seen in traits associated with social tendencies (using social connectivity as a proxy). Variance in the social environment (i.e., environmental variance) played a large role in shaping observed phenotypic variation in social connectivity. However, all six of the social network measures examined were weakly heritable, which suggests that there is also a genetic basis for behavioral variation, allowing selection to occur. This dissertation emphasizes the importance of examining both antipredator behavior and sociality using multiple experiments, observations, and measures, while also considering the importance of study species and habitat complexity. The relationship between antipredator behavior and social connectivity is not straightforward and can vary greatly between study systems. Although many of my predictions were not supported, I did find evidence that blue monkeys are receptive to heterospecifics, vary their acute antipredator responses and vigilance based on social relationships with conspecifics, adjust their antipredator vigilance according to spatial positioning, and potentially discriminate between alarm callers. The findings presented here expand our knowledge of how animals learn about predation risk by being attentive to conspecifics and heterospecifics.
525

Testing Spillover of Nocturnal Predators in Agroecosystems: The Influence of Ditch Type and Prey Availability

Woloschuk, John Robert 26 November 2019 (has links)
No description available.
526

The effect of anthropogenic habitat modification on insect-mediated ecosystem services

Maran, Audrey Marie 06 August 2020 (has links)
No description available.
527

Re-evaluation of north-temperate reservoir food web interactions and their assessment

Dillon, Rebecca January 2020 (has links)
No description available.
528

A New Perspective on Giving-Up Density Experiments and the Landscape of Fear

McMahon, Jordan D 04 May 2018 (has links)
Non-consumptive effects that predators have on prey are important to ecosystems. The perceived risk of predation can alter feeding behavior. Giving-up density (GUD) experiments have been a foundational method to evaluate perceived predation risk, but rely on the assumption that food preferences are absolute. However, nutritional preferences are context dependent and can change with risk. In my first chapter, I used spiders and grasshoppers to test the hypothesis that covariance in nutritional preferences and risk may confound the interpretation of GUD experiments. My results demonstrate that predation risk and nutritional preferences covary and can confound interpretation of GUD experiments. In my second chapter, I use a behavioral observation experiment to further explore non-consumptive effects, as well as the movement of prey in response to predation risk.
529

Fire ant response to management of native grass field buffers

Hale, Sarah Lucinda 07 August 2010 (has links)
Imported fire ants are invasive and cause injury to people, crops, livestock and wildlife. Disturbance may increase abundance and activity of fire ants. However, native grass field buffers established for grassland birds require periodic disturbance. I experimentally tested if fire ant mound density and foraging activity changed after burning and disking in native grass buffers and examined relationships among fire ants, vegetation, and grassland bird and butterfly metrics in undisturbed buffers. In 2008, disking increased mound density and foraging activity, but burning did not. In 2009, disking had no effect, but effects of disking the previous season persisted. Fire ant metrics were not related generally to bird or butterfly metrics. Mound density and foraging activity were related negatively to grass cover and related positively to forbs. Burning had less influence on abundance and activity of fire ants, and may better conserve grassland habitats in areas with fire ants.
530

Utilizing Acoustic Methods to Identify Bat Species, and to Assess Their Habitat Use and Perception of Owls

Janos, Gregg A. 12 April 2013 (has links)
No description available.

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