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Species have specific tolerances to a variety of environmental variables including temperature, dissolved oxygen (DO) and turbidity. Changes in either of these variables can therefore be expected to affect predator-prey interactions in shallow water ecosystems. Temperature drives the metabolic rates of poikilotherms, including fish. Hypoxic conditions generally affect larger fishes to a greater degree than smaller fishes, though the presence of physostomous swim bladders in certain species can alter that relationship. Finally there are species of fish that rely on vision for food acquisition while other species rely on other senses such as chemical cues. Changes in turbidity levels could therefore affect foraging efficiency of visual foragers. This thesis examines the role that each of these environmental variables (temperature, DO and turbidity) can have on community composition and therefore predator prey interactions, with a specific focus on the role of temperature in structuring predator-prey interactions. Laboratory, field and theoretical studies suggest that as temperature increases, encounter rates between predators and prey will increase. Prey are more active, spend more time foraging, and increase their use of risky habitats in warmer environments in laboratory experiments. In the field, prey and predator activity and/or abundance is positively related to temperature. These laboratory and field studies suggest that temperature increases should result in increased predation rtes of prey. Finally, the results of a dynamic state dependent optimization model also suggest that periods of warming will result in a lowering of the probability of survival of the fathead minnow, Pimephales promelas, a prey species, over the-ice free season. A reduction in DO levels in aquatic ecosystems results in a reduction in the number of and/or activity of predators present. This should result in a reduction in predation risk to prey. However, when endothermic predators are factored in to this equation, this reduction in risk may not occur. The presence of avian predators of small forage fish are directly related to the level of DO in the water, regardless of the abundance of prey fish present. This relationship is likely a result of behavioural decisions of prey that occurs in hypoxic conditions. In periods of low DO, prey fishes may exploit areas of higher DO that are closer to the surface of the waters. While their piscine predators may not be able to tolerate the low DO levels regardless of the position of prey in the water column, avian predators appear to be able to cue in to this increase in availability of potential prey, reducing any benefits that might occur by occupying surface areas where DO levels might be slightly higher than lower in the water column. As compared to temperature and DO, turbidity does not appear to affect the potential risk of predation to forage fish. The catch per unit effort (CPUE) of foragers who rely on vision and those that rely on chemical cues to forages, were not related to turbidity levels. Turbidity levels were also not related to the abundance of avian predators. This suggests that in this generally turbid, shallow water ecosystem, changes in turbidity do not affect the overall species composition of the system. Predator-prey interactions in the system are also not likely to be affected by turbidity. In contrast to this, temperature and DO are likely to influence the interactions between predators and their prey in a shallow water ecosystem. Both increases in temperature and decreases in DO may result in increases in predation pressure on prey. While temperature increases will likely result in increased predation on prey by piscine predators, a reduction in DO, which often occurs as temperature increases, will likely result in increased predation on prey by avian predators, even as predation pressure by piscine predators decrease.

In the first longterm field study of the fossa, mean adult body mass measured was, in males, 7.4 kg (n=17, s.d.=1.2), and, in females, 6.1 kg (n=11 females, s.d.=0.6). Sexual size dimorphism was most marked in canine width. 376 scats yielded 554 prey items, of which the majority were lemurs (>50%)m, tenrecs and snakes. Incidence of prey in scats correlated positively with abundance. Scat composition varied with season, but not with year nor gender of fossa. Sexual dimorphism could not therefore be explained as niche separation. Home ranges were, for two males, 22.74 km² and 26.20 km², and for two females, 12.69 km² and 7.84 km². These, and incomplete ranges of six others, overlapped between males but not females, and were larger in the dry season than in the wet season. Censuses and radio-tracking generated consistent population density estimates, averaging 0.17 adults per km², substantially lower than predicted from body size, and indicating that even Madagascar's largest reserve may not hold a viable population of fossas. The unique mating system resembled a lek: females mated with multiple males on traditional sites. One female occupied a site at a time, for up to one week. The system may benefit species with low population density, by increasing mate choice for females and facilitating mate location for males. It may also reduce sexual harassment of oestrous females. Males fought at the sites, but no size-related advantage in male mating success was observed. A different mating system was predicted from the home range data. The first discovery was made of transient masculinization of a female mammal. Juvenile female fossas (n=8) exhibited an enlarged, spinescent clitoris supported by an os clitoridis, and a pigmented secretion that in adults was confined to males. Masculinization was hypothesized to reduce sexual harassment of young females.

Through wastewater entering aquatic environments, aquatic insects are continuously exposed to pharmaceuticals including neurologically active antihistamines. The antihistamine hydroxyzine has previously been found to lower activity in damselflies and to reach 2000 times the concentration of surrounding water in damselfly tissue. The purpose of this short-term exposure study was to investigate if hydroxyzine also bioaccumulates in dragonflies and if dilute hydroxyzine (362 ± 50, mean ng/l ± SD) have effects on predator-prey interactions between dragonfly Aeshna grandis and damselfly Coenagrion hastulatum larvae, i.e. number of attacks and predation success. Predators and prey were captured and exposed during one, three or five days (with controls) before taking part in predation experiments; Dragonflies were put in separate containers with six damselflies, they were video recorded and attacks and predated damselflies noted during four hours. Tissue concentrations of hydroxyzine were analyzed from all dragonflies and a subsample of the damselflies showing a mean bioconcentration factor (BCF) of 27 and 7 respectively, surprisingly much lower than previous research. There was no difference in attack rate or predation efficiency between controls and exposed dragonflies. However, dragonflies exposed for five days were found to attack more and capture more prey than dragonflies exposed for one day, a change that was not seen in the controls. This confounding factor motivates further studies to clarify if hydroxyzine after a period of exposure can have a sublethal effect altering foraging and/or predator avoidance traits with the net result of increased predation success for dragonflies in the predator-prey interaction between dragonflies and damselflies.

Evolution can occur rapidly, along timescales that are traditionally regarded as 'ecological'. Despite growing acceptance among biologists of rapid evolution, a strong paradigm of contemporary evolution is still absent in many sub-disciplines. Here I apply a contemporary evolution viewpoint to conservation biology. Specifically, I examine the impact of cane toads (Bufo marinus) on Australian snakes. Toads were introduced into Australia in 1935, have spread rapidly and represent a novel, extremely toxic prey item to na�ve Australian predators (including snakes). Based on dietary preferences and geographic distributions I find that 49 species of Australian snake are potentially at risk from the invasion of the toad. Furthermore, examination of physiological resistance to toad toxin in 10 of these �at risk� species strongly suggests that most species of Australian snake are poorly equipped to deal with a likely dose of toad toxin. Even species that are highly resistant to toad toxin (such as the keelback, Tropidonophis mairii) face indirect fitness costs associated with consuming toads. Within a population of snakes however, the impact of toads is unlikely to be random. For example, the examination of several component allometries describing the interaction between snakes and toads revealed that, within a species, smaller snakes are more likely to ingest a fatal dose of toad toxin than are larger snakes. Further consideration of the interaction between snakes and toads suggests that toads will not only be exerting differential impact on snakes based upon morphology, but also exert non-random selection on prey preference and resistance to toad toxin in snake populations. To examine the possibility of a morphological response by snakes to toads, I examined changes in the body size and relative head size of four species of snake as a consequence of time since exposure to toads. Two of the species (green treesnakes and red-bellied blacksnakes) are predicted to face strong impacts from toads. These two species showed an increase in mean body size and a decrease in relative head size as a consequence of time since exposure to toads; both changes in an adaptive direction. In contrast, the other two species (keelbacks and swampsnakes) are predicted to face much lower impact from toads, and these two species showed little or no evidence of morphological change associated with time since exposure to toads. These results indicate an adaptive change in morphology at a rate that is proportional to the predicted level of impact for each species, strongly suggesting an evolved response. Red-bellied blacksnakes (a toad-vulnerable species) were further assessed for evolved responses in prey preference and toxin resistance. Comparisons between toad-exposed and toad-na�ve populations of blacksnakes revealed that snakes from toad-exposed populations exhibited slightly higher resistance to toad toxin and a much-reduced tendency to eat toads, when compared with toad-na�ve snakes. Na�ve snakes exhibited no tendency to learn avoidance of toxic prey, nor were they able to acquire resistance to toxin as a result of several sub-lethal doses, suggesting that the observed differences between populations is evolved rather than acquired. Together, these results strongly suggest that blacksnakes are exhibiting an evolved shift in prey preference and toxin resistance as a consequence of exposure to toads. Thus, it appears that snakes are exhibiting adaptation at multiple traits in response to exposure to toads. Given the high likelihood that these adaptive shifts have an evolved basis, it appears that the impact of toads will decrease with time in many snake populations. But what about toads? Because the outcome of the interaction between a toad and a snake is also mediated by the body size and relative toxicity of toads, it is important to understand how these traits vary in space and time. Exploratory analysis revealed that toads exhibit a decrease in body size and a decrease in relative toxicity as a consequence of time since colonisation, indicating that their impact on native predators decreases with time. Additionally, there appears to be meaningful spatial variation in toad relative toxicity, indicating that some populations of native predators are facing higher impact from toads than others. Overall, these results clearly indicate the importance of assessing the potential for rapid evolutionary response in impacted systems. Doing so may provide evidence that some species are in less trouble than originally thought. Additionally, and as more data accumulate, it may be possible to characterise certain categories of environmental impact by their potential for eliciting adaptive response from �impacted� species. This approach has strong implications for the way conservation priorities are set and the way in which conservation dependent populations are managed.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Vita. Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Walleye (Sander vitreus) culture for maintenance stocking in lakes has always been fraught with challenges. Their propensity to cannibalize at an early age and their reluctance to accept a prepared diet make the production of advanced fingerlings extremely costly. Hatchery reared walleye fingerlings are extremely vulnerable to predation when stocked into impoundments with established fish populations. This study was conducted to determine if fish culturists could increase walleye survival by exposing summer fingerlings to fish predators and/or providing experience with piscivory before being stocked for recreational angling. Tank studies were conducted to minimize environmental variation among experimental treatments and replicates. In 2005, 5 treatment groups were tested, including a group that was allowed to feed on zooplankton only, a group that was habituated to feed, a group that was exposed to a fish predator, a group that was given an opportunity to prey on fish, and a group that was exposed to a fish predator and given an opportunity to prey on fish. In 2006, the feed habituated group was lost to disease, but a feed habituated group that was given experience avoiding fish predators and opportunity to forage on fish prey and a feed habituated group that was given opportunity to forage on fish prey were added. Walleye fingerlings from the 5 treatment groups in 2005 were placed in tanks with cover and a 250 mm largemouth bass as a predator. Walleye survival was measured after 24 hours; no significant differences in survival were detected among treatment groups in 2005. In 2006, 10 walleye fingerlings from each of the 6 treatment groups were added to tanks fitted with a cedar reef for cover and two 250 mm largemouth bass. Fingerling walleye survival was highest in the feed habituated prey exposed group and the feed habituated predator and prey exposed group after 14 days; higher survival in these groups may have been due to their larger initial size. Pond studies were also conducted in 2005 and 2006 to evaluate differences in survival among treatment groups under conditions that more closely resemble environments into which fingerling walleye are stocked. Twelve 0.4-hectare ponds were prepared by placing 15 adult bluegill (~200 mm total length) and 5 adult largemouth bass (~300 mm total length) into each pond along with a 6.5 m cedar reef for cover. Survival of fingerling walleye in ponds was measured on days 3, 7, 15, 30, 60, 90, and 120 post-stocking. Pond and tank trials indicated no apparent post-stocking increase in survival for walleye fingerlings that were given prior exposure to predators or fish prey. Additionally, a multiple batch tagging / marking procedure was needed to separate walleye fingerling groups in ponds and tanks. Visible Implant Elastomer (VIE) tags and liquid nitrogen freeze brands were chosen and retention rates were determined for fingerling walleye, as little published information on retention rates for these techniques was available. VIE tags were lost steadily over time (41.67% retention at 270 days), while freeze branding showed much better retention (87.88% retention at 270 days).

We analyzed the relationship between prey capture and nematocyst distribution in the tentacles of the ambush predators, Aglantha digitale and Proboscidactyla flavicirrata, and the filter feeders, Clytia gregaria and Mitrocoma cellularia. we used video observations to compare capture locations of Artemia salina nauplii relative to the bell margin of each species. Tentacle pictures were analyzed to determine if nematocyst abundance changes along their length. By analyzing behavior and morphology simultaneously, we found that the ambush predators A. digitale and P. flavicirrata plus Sarsia tubulosa have higher nematocyst density at the tentacle tips and tend to capture more prey toward the tips. In contrast, the filter-feeders Aequorea victoria, C. gregaria and M. cellularia capture most of the prey close to the body, where they also show a slight increase in nematocyst densities.

During the last twenty years marked declines in Peregrine Falcon populations have occurred in many parts of the world (Hickey, 1969). During recent years the peregrine has been placed on the list of Endangered Species. Several factors have been suggested as the cause of its decline. These include changing climatic conditions (Porter and White, 1973), human disturbance (Mattox, pers. comm.), and introduction of chlorinated hydrocarbons as pesticides into the environment (Ratcliffe, 1970). The third factor, introduction of chlorinated hydrocarbons, has occurred on the American, European and Asian continents. Even peregrines nesting in locations far from human population concentrations are exposed to chemical pollutants on migratory flights south, in nesting areas and in the wintering range. Most of the small birds utilized by the peregrine as prey in the north also migrate south every winter, many moving into farming areas where insecticides are frequently used. By feeding in these areas the passerines accumulate substantial amounts of chlorinated hydrocarbons which are stored in fat tissues. As the peregrines feed on these small birds, body levels of chlorinated hydrocarbons gradually increase. If subsequent levels·are high enough, they may cause death (Porter, 1972). In most cases, however, lethal levels are never reached: instead the lower levels produce eggshell thinning and breakage (Porter and Wiemeyer, 1969) which may be an important reason for world-wide decline in peregrine populations (Hickey and Roelle, 1969). Peregrines in the western United States have shown a 20% decrease in eggshell thickness since DDT was introduced (Enderson and Craig, 1974).

Understanding how species respond to variations in weather patterns will be crucial to improve our predictions about how species will cope with climate change. The Verreaux's Eagle (Aquila verreauxii) and its primary prey species the Rock Hyrax (Procavia capensis) and Yellow-spotted Hyrax (Heterohyrax brucei) have been monitored by a long-term citizen science project in the Matobo Hills, Zimbabwe. A previous study associated rainfall patterns with the establishment, breeding density and productivity of Verreaux's Eagles. Fluctuations in hyrax populations have been attributed to fluctuations in rainfall and drought. However, these studies have been limited by the use of total annual rainfall instead of targeted rainfall periods of when biological outcomes are most sensitive to weather phenomena. This study explored critical climate sensitivity windows influencing the Verreaux's Eagle's reading performance and the abundance of its main prey species. We used observations of 109 nests over 37 years (1984-2019) and counts from 20 hyrax den sites for 13 years (1993-2005), together with remotely sensed rainfall data. The probability of attempting to breeding and the probability of producing a fledgling was negatively associated with rainfall. For breeding attempt, the rainfall during June and July, 11-10 months before laying was the most relevant, whereas, for productivity, the rainfall during December to March, nine-five months before fledging was the most relevant. However, the relationship between the rainfall signal and breeding productivity was not significant. Hyrax abundance had a negative quadratic relationship with mean rainfall against their respective climate windows, whereby the abundance of adult and sub-adult hyrax increased with rainfall during July–September but declined thereafter at greater rainfall levels. The abundance of hyrax did not have a significant relationship with the breeding outcomes of the Verreaux's Eagles. This study shows the complexity of the causal relationships between climate and biological outcomes and also the value of long-term data to understanding the impacts of variations in weather patterns to better understand predator-prey dynamics.