Description : Predators and omnivores shape community structure and function by consuming (i.e. consumptive effects; CEs) and 'scaring' (i.e. nonconsumptive effects; NCEs) prey. Thus, predicting the consequences of predator-prey interactions has been a major focus of ecological research for several decades. For instance, understanding the mechanism(s) by which predators induce trophic cascades (i.e. CEs vs. NCEs) is important because the nature of this indirect interaction can critically influence ecosystem-level processes such as energy flow and nutrient cycling. Despite the vast literature on predator-prey interactions, few studies tested the role of predator and prey traits on the outcomes of these interactions. Recognizing this, I tested how predator traits [e.g. hunting mode (Chapter 1) and facultative omnivory (Chapter 2 & 3)] and prey traits [e.g. habitat domain range (Chapter 1)] impact the outcome of predator-prey interactions in natural systems. In Chapter 1, I examined the trait-mediated indirect interaction (TMII) and total indirect interaction (TII) produced during interactions between an active, broad habitat domain range (BHDR) ladybeetle predator ( Naemia seriata) and its narrow habitat domain range (NHDR) prey (scale insects; Haliaspsis spartinae). I exposed scale insects to nonlethal and lethal ladybeetle predators in laboratory mesocosms for 15 weeks. I measured how these interactions indirectly impacted the growth of the scale insect's host plant (cordgrass; Spartina foliosa) and the population density of scale insects. Contrary to theoretical predictions based on these predator and prey traits, nonlethal ladybeetles did not induce TMIIs. However, lethal ladybeetles increased cordgrass total and root dry biomass by 36% and 44% (respectively), suggesting the presence of strong density-mediated indirect interactions (DMIIs). Additionally, both lethal and nonlethal ladybeetles reduced scale insect population density. My findings suggest that DMIIs, rather than TMIIs, can result from interactions between active, BHDR predators and NHDR prey. In Chapter 2, I used three primary experiments to assess the relationship between habitat use (based on the availability of animal and/or plant prey resources) and performance for an important insect omnivore (ladybeetles). First, I used field manipulations of resource availability (i.e. scale insects and cordgrass pollen) to examine the habitat use of ladybeetle predators. Second, I conducted a series of no-choice laboratory assays to compare the performance (fecundity and longevity) of ladybeetles on these different resources. Third, I quantified adult ladybeetle preference for olfactory cues from cordgrass with and without scale insects using a ytube olfactometer. In the field, adult ladybeetles selectively used plots containing scale insects. In the lab, diets containing scale insects maximized both adult and larval ladybeetle longevity, and adult fecundity. Adult ladybeetles were attracted to chemical cues associated with scale insects over distances of 10s of centimeters. Overall, my findings suggest that the habitat use and performance of ladybeetles are strongly linked, with ladybeetles preferentially using habitats that maximize their individual performance. Collectively, my dissertation suggests that the functional traits of predators and prey can provide useful insights into when, where, and how predators may exert top-down effects on ecological communities.
Description : This book addresses the fundamental issues of predator-prey interactions, with an emphasis on predation among arthropods, which have been better studied, and for which the database is more extensive than for the large and rare vertebrate predators. The book should appeal to ecologists interested in the broad issue of predation effects on communities.
Description : 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.
Description : 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.