Throughout their lives, prey organisms must balance the tradeoff between fitness-related activities and the risk of predation. To successfully mediate such tradeoffs, prey must have an accurate method to gauge current predation risk. For many aquatic organisms, the use of chemosensory information has been shown to be a ubiquitous and useful tool in mediating predation risk. The chemical cues to which aquatic organisms respond include the odour of known predators and the odour of a damaged conspecific or known or closely related heterospecific. In fishes, the response to damage-released cues from conspecifics or closely related heterospecifics has been shown to be innate, while the response to distantly related unknown heterospecific cues are likely learned. In a series of laboratory and field studies I examined the role of learning in the ability of fathead minnows to respond to damage-released cues of brook stickleback as an indication of predation risk. My results indicate that minnows from a population without stickleback do not recognize stickleback cues as dangerous. However, following the introduction of stickleback, minnows learn to recognize stickleback cues as dangerous. Further study indicated a low ratio of stickleback to minnows in a given population will decrease the likelihood of learning when compared with a similar sized population containing a higher ratio of stickleback to minnows. I also demonstrated that an increase in habitat complexity decreases the ability of minnows to learn to recognize stickleback cues. Studies have further demonstrated that in the face of predation (as indicated by chemical cues from minnows and stickleback) minnows will decrease their antipredator response when in the presence of a fish shoal, especially a shoal of conspecifics. Finally, an examination of the effects of a minnows length, body condition and breeding status indicate that morphological parameters can play a significant role in the intensity of response to he.

The indirect effects of predation have been the focus of many studies on predator-prey interactions. One way in which predators can indirectly affect prey life history is by altering habitat selection. For prey that occupy different habitats as adults than as larvae, it is likely important for adults to consider potential predators of their offspring when selecting a suitable place to lay their eggs. I studied the ability of adult 'Enallagma' damselflies to detect fish, which, for some species, are important predators of damselfly larvae. I found that adult 'Enallagma ebrium' could detect and avoid fish during visits to a site, but that oviposition frequency and duration were unaffected by fish presence. Subsequently, I attempted to establish how adults of three 'Enallagma' species detect fish, but was unsuccessful in determining whether visual presence or chemical cues were used in predator detection. As well, I performed additional experiments on these three species to determine whether fish chemical cues would affect the number of eggs released by females during oviposition. For each species, I found that the number of eggs released was not affected by the presence of fish chemical cues. Other researchers have established that larval damselflies are capable of visual predator detection, but there is also evidence that damselfly larvae can detect predator chemical cues if they are paired with the cues of dead conspecifics. Therefore, I designed a study to determine the relative importance of visual and chemical cues to predator detection by larvae. Frequency and duration of larval behaviours were reduced by visual fish presence and by fish chemical cues. As well, the season in which the experiment was performed produced a significant difference in the frequency of behaviours, with a higher frequency in the spring than the fall when the larvae are in diapause.

Research on olfaction in fishes: historical aspects; Structure and function; Development and regeneration of the olfactory organ in rainbow trout; Comparative morphology of the peripheral olfactory organ in teleosts; Synaptic organization of the olfactory bulb and central projection of the olfactory tract; Taste organ in the barbel of the bullhead; Chemoreceptive mechanisms; Responses of olfactory receptor cells to electrical and chemical stimulation; High sensitivity and specificity of olfactory and gustatory receptors of catfish to amino acids; Structure-activity relationships of amino acids as olfactory stimuli; Biochemical aspects of amino acid receptors in olfaction and taste; Neuronal correlates of olfactory behavior in goldfish; The role of olfaction in the orientation of fishes; Chemoreception in the lateral-line organ; Role of chemoreception in feeding; Taste receptor stimulation and feeding behavior in the puffer; Chemical stimulation of feeding behavior; Identification of the gustatory feeding stimulants; Baits in fisheries with emphasis on the North Atlantic cod fishing industry; Role of chemoreception in social behavior and migration; Chemical signals in communication; The adaptive significance of the alarm substance-fright reaction system; The role of chemoreception in salmonid homing; Chemoreception and water pollution; Chemoreception and aquatic pollutants; Structure and function of the olfactory mucosa of migrating baltic trout under environmental stresses, with special reference to water pollution.

Predators affect prey populations both through consumption and by inducing antipredator trait responses. In the mere presence of predators, many prey modify traits in order to reduce their risk of being consumed. Predation risk-induced trait responses (hereafter 'trait responses') are numerous and universal across ecosystems and across different taxa, from protists to large mammals. Increasing attention is being given to the proposition that trait responses can have large effects on prey fitness, with ensuing effects on prey population growth and interacting species. A thorough understanding of the role of such predation risk effects is important for the ecological theory of basic properties such as resilience and biodiversity, and for ecological models used in natural resources management.While there are many studies that demonstrate a variety of trait responses in different taxa and examine the drivers of trait responses, it is still difficult to predict when trait responses will translate to population and community-level effects. The majority of theories and studies of trait responses have been conducted in simplified food webs such as predator-prey pairs. However, to examine the contribution of predation risk effects in addressing ecological questions, there is a need to understand how trait responses operate in larger food webs. To scale up from simplified systems, fundamental properties of populations and communities need to be considered including whether there is variation and contingency in trait responses among life history stages and similar species of prey. While there is a theoretical basis for expecting variation, empirical examples in a natural setting are lacking.My dissertation research empirically examines the variation and contingency of behavioral trait responses induced by a fish predator within a diverse assemblage of zooplankton prey. Experiments were conducted in mesocosms with and without fish kairomone (produced by caged fish); the effect of kairomone on the position of zooplankton is used as a measure of behavioral response. Chapter 1 examines variation in behavioral responses among life history stages of copepods. The responses were highly stage-dependent, with nauplii shifting in the opposite direction than copepodites and adults. Chapters 2 and 3 examine variation in cladoceran behavioral responses and assess if the expression and magnitude of responses is contingent on differences in predation risk among taxa. In trying to understand the variation in trait responses among prey, it might be expected that more vulnerable prey would exhibit larger trait responses. Such positive relationships between trait responses and predation risk have been exhibited in some systems. We compared the relationship between behavioral responses and metrics of predation risk across cladocerans. Metrics included relative predation rate and net effect of the predator on density on each taxon (measured from a treatment with uncaged fish) as well as cladoceran body size and taxonomic identity (family). While cladocerans exhibited strong variation in behavioral responses, we did not find larger trait responses in more vulnerable prey.Taken together, the chapters within this dissertation demonstrate there can be considerable variation in trait responses among prey and reinforces the complex nature of factors underlying trait responses. Explicit consideration of variation in trait responses and trade-offs that govern them can lead to better insight when scaling up the study of predation risk effects and their incorporation into models.

Predation strongly influences population dynamics and community structure. Besides the direct consumption of prey, however, predators also have important non-consumptive effects (NCEs). During early life stages, marine fishes experience substantial predatormediated mortality, and thus may also experience NCEs, including a physiological stress response. In this study I investigate the nonlethal effects of a piscine predator (kelp bass, Paralabrax clathratus) on the behavior, physiological stress (measured by cortisol concentration), individual growth, and subsequent survival of juvenile giant kelpfish (Heterostichus rostratus). The spatial distribution of giant kelpfish changed in response to visual exposure to kelp bass vs. a similarly sized non-predatory fish and a control (no fish), indicating that giant kelpfish visually recognize predators. Giant kelpfish also respond to predation threat through elevated cortisol concentrations, but there was no difference in cortisol concentration when they were directly exposed to a predator or a non-predator. When giant kelpfish fed ad libitum were exposed to a predator or to a control during crepuscular periods for 2 wk, fish that experienced a predator exhibited slower growth, suggesting that the physiological response per se was responsible (and not lower feeding activity). When subjected to treatments of structural habitat complexity (densities of artificial eelgrass), the highest cortisol concentrations exhibited by giant kelpfish were at medium densities of eelgrass, likely due to habitat-mediated predator movement and thus encounter rates with prey. Most importantly, prior exposure to predation threat resulted in lower predation mortality, possibly due to a faster escape response from elevated cortisol concentrations. These results demonstrate that predation threat elicits a stress response in giant kelpfish, and that this response may have demographic consequences in the form of reduced individual growth and lower predation risk.