Humans, being visually oriented, are well versed in camouflage and how animals hide from predators that use vision to locate prey. However, many predators do not hunt by sight; they hunt by scent. This raises the question: do survival mechanisms and behaviors exist which allow animals to hide from these olfactory predators? If so, what are they, a

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Trophic cascades—the top-down regulation of ecosystems by predators—are an essential aspect of ecosystem function and well-being. Trophic cascades are often drastically disrupted by human interventions—for example, when wolves and cougars are removed, allowing deer and beaver to become destructive—yet have only recently begun to be considered in the development of conservation and management strategies. Trophic Cascades is the first comprehensive presentation of the science on this subject. It brings together some of the world’s leading scientists and researchers to explain the importance of large animals in regulating ecosystems, and to relate that scientific knowledge to practical conservation. Chapters examine trophic cascades across the world’s major biomes, including intertidal habitats, coastal oceans, lakes, nearshore ecosystems, open oceans, tropical forests, boreal and temperate ecosystems, low arctic scrubland, savannas, and islands. Additional chapters consider aboveground/belowground linkages, predation and ecosystem processes, consumer control by megafauna and fire, and alternative states in ecosystems. An introductory chapter offers a concise overview of trophic cascades, while concluding chapters consider theoretical perspectives and comparative issues. Trophic Cascades provides a scientific basis and justification for the idea that large predators and top-down forcing must be considered in conservation strategies, alongside factors such as habitat preservation and invasive species. It is a groundbreaking work for scientists and managers involved with biodiversity conservation and protection.

Much of our understanding about insect predator-prey dynamics has been due to studies on insect parasitoids. But do true predators such as ladybird beetles really operate in a similar way and how does this affect their use in biological control? The extensive literature on ladybirds as biocontrol agents shows that their size and rate of development is very dependent on the nature of their prey. This volume explores basic ladybird biology, their association with their prey and its effect on development rate and body size. Optimal foraging theory, field observations and laboratory experiments are used to illustrate how ladybird larvae maximise their rate of energy intake, and ladybird adults their fitness. The interdependence of these life history parameters is then used to develop a simple predator-prey model which, with an analysis of the literature, highlights the specific attributes of potentially successful biocontrol agents for all those interested in predator-prey dynamics.

In this study of arthropod predador-prey systems Michael Hassell shows how many of the components of predation may be simply modeled in order to reveal their effects on the overall dynamics of the interacting populations. Arthropods, particularly insects, make ideal subjects for such a study because their generation times are characteristically short and many have relatively discrete generations, inviting the use of difference equation models to describe population changes. Using analytical models framed in difference equations, Dr. Hassell is able to show how the detailed biological processes of insect predator-prey (including host-parasitoid) interactions may be understood. Emphasizing the development and subsequent stability analysis of general models, the author considers in detail several crucial components of predator-prey models: the prey's rate of increase as a function of density, non-random search, mutual interference, and the predator's rate of increase as a function of predator survival and fecundity. Drawing on the correspondence between the models and field and laboratory data, Dr. Hassell then discusses the practical implications for biological pest control and suggests how such models may help to formulate a theoretical basis for biological control practices.

Many animals regulate their population density by patterns of behavior that would be easy to explain if the forces of natural selection acted to optimize group properties. But Darwinian selection acts on individuals, not groups, and most simple theories have shown group selection to be too slow ever to oppose individual selection successfully. In this book Michael Gilpin presents a model, based on predator-prey dynamics, wherein nonlinear effects are important, so that small advantages to the selfish individual are nonlinearly amplified into disaster for his group. The result is that group selection can be rapid and powerful. Of course many instances of apparent group selection can be explained by kin selection; in other cases, close examination reveals that seemingly altruistic behavior directly benefits the individual genotype as well as the group. The value of the monograph is that it provides a robust model in which group selection, pure and unadulterated, can be seen to work.

These notes correspond to a set of lectures given at the Univer sity of Alberta during the spring semester, 1973. The first four sec tions present a systematic development of a deterministic, threshold model for the spraad of an infection. Section 5 presents some compu tational results and attempts to tie the model with other mathematics. In each of the last three sections a separate, specialized topic is presented. The author wishes to thank Professor F. Hoppensteadt for making available preprints of two of his papers and for reading and comment ing on a preliminary version of these notes. He also wishes to thank Professor J. Mosevich for providing the graphs in Section 5. The visit at the University of Alberta was a very pleasant one and the author wishes to express his appreciation to Professors S. Ghurye and J. Macki for the invitation to visit there. Finally, thanks are due to the very competent secretarial staff at the University of Alberta for typing the original draft of the lecture notes and to Mrs. Ada Burns of the University of Iowa for her excellent typescript of the final version. TABLE OF CONTENTS 1. A Simple Epidemic Model with Permanent Removal . . . • . . . 1 2. A More General Model and the Determination of the Intensity of an Epidemic. 10 21 3. A Threshold Model. 4. A Threshold Model with Temporary Immunity. 34 5. Some Special Cases and Some Numerical Examples 48 A Two Population Threshold Model . 62 6.