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.

Twenty-four essays from a symposium sponsored by the Ecological Society of America, Fort Collins, CO, 1984. The focus is on a single theme: that the mere presence of a predator can influence interactions between two or more competing species in many important ways, all of which have previously been included under the nebulous term effects. Annotation copyrighted by Book News, Inc., Portland, OR

Introduces readers to key case studies that illustrate how theory and data can be integrated to understand wildlife disease ecology.

Whatever theory may be advanced to explain diurnal migration, the underlying reactions involved must be demonstrated conc- sively in the laboratory before the explanation can be ?nally accepted George L. Clarke 1933 p. 434 In oceans and lakes, zooplankton often make diel vertical migrations (DVM), descending at dawn and coming up again in late afternoon and evening. The small animals cover distances of 10–40 m in lakes or even a few hundred metres in the open oceans. Although not as spectacular as migrations of birds or the massive movements of large mammals over the African savannas, the numbers involved are very large and the biomass exceed the bulk of the African herds. For example, in the Antarctic oceans swarms of “Krill” may cover kilometres across, with thousands of individuals per cubic metre. These Euphausiids are food for whales, the most bulky animals on earth. Zooplankton are key species in the pelagic food web, intermediary between algae and ?sh, and thus essential for the functioning of the pelagic community. Prey for many, they have evolved diverse strategies of survival and DVM is the most imp- tant one. Most ?sh are visually hunting predators and need a high light intensity to detect the often transparent animals. By moving down, the well-lit surface layers are avoided but they have to come up again at night to feed on algae.

This 1993 book documents the importance of trophic cascades in aquatic ecology.

Individual-based models are an exciting and widely used new tool for ecology. These computational models allow scientists to explore the mechanisms through which population and ecosystem ecology arises from how individuals interact with each other and their environment. This book provides the first in-depth treatment of individual-based modeling and its use to develop theoretical understanding of how ecological systems work, an approach the authors call "individual-based ecology.? Grimm and Railsback start with a general primer on modeling: how to design models that are as simple as possible while still allowing specific problems to be solved, and how to move efficiently through a cycle of pattern-oriented model design, implementation, and analysis. Next, they address the problems of theory and conceptual framework for individual-based ecology: What is "theory"? That is, how do we develop reusable models of how system dynamics arise from characteristics of individuals? What conceptual framework do we use when the classical differential equation framework no longer applies? An extensive review illustrates the ecological problems that have been addressed with individual-based models. The authors then identify how the mechanics of building and using individual-based models differ from those of traditional science, and provide guidance on formulating, programming, and analyzing models. This book will be helpful to ecologists interested in modeling, and to other scientists interested in agent-based modeling.