Monographs in Population Biology – serie

A number of scholars have found that concepts such as mutation, selection, and random drift, which emerged from the theory of biological evolution, may also explain evolutionary phenomena in other disciplines as well. Drawing on these concepts, Professors Cavalli-Sforza and Feldman classify and systematize the various modes of transmitting "culture" and explore their consequences for cultural evolution. In the process, they develop a mathematical theory of the non-genetic transmission of cultural traits that provides a framework for future investigations in quantitative social and anthropological science. The authors use quantitative models that incorporate the various modes of transmission (for example, parent-child, peer-peer, and teacher-student), and evaluate data from sociology, archaeology, and epidemiology in terms of the models. They show that the various modes of transmission in conjunction with cultural and natural selection produce various rates of cultural evolution and various degrees of diversity within and between groups.The same framework can be used for explaining phenomena as apparently unrelated as linguistics, epidemics, social values and customs, and diffusion of innovations. The authors conclude that cultural transmission is an essential factor in the study of cultural change.

Despite often violent fluctuations in nature, species extinction is rare. California red scale, a potentially devastating pest of citrus, has been suppressed for fifty years in California to extremely low yet stable densities by its controlling parasitoid. Some larch budmoth populations undergo extreme cycles; others never cycle. In Consumer-Resource Dynamics, William Murdoch, Cherie Briggs, and Roger Nisbet use these and numerous other biological examples to lay the groundwork for a unifying theory applicable to predator-prey, parasitoid-host, and other consumer-resource interactions. Throughout, the focus is on how the properties of real organisms affect population dynamics. The core of the book synthesizes and extends the authors' own models involving insect parasitoids and their hosts, and explores in depth how consumer species compete for a dynamic resource. The emerging general consumer-resource theory accounts for how consumers respond to differences among individuals in the resource population. From here the authors move to other models of consumer-resource dynamics and population dynamics in general.Consideration of empirical examples, key concepts, and a necessary review of simple models is followed by examination of spatial processes affecting dynamics, and of implications for biological control of pest organisms. The book establishes the coherence and broad applicability of consumer-resource theory and connects it to single-species dynamics. It closes by stressing the theory's value as a hierarchy of models that allows both generality and testability in the field.

Throughout the twentieth century, biologists investigated the mechanisms that stabilize biological populations, populations which--if unchecked by such agencies as competition and predation--should grow geometrically. How is order in nature maintained in the face of the seemingly disorderly struggle for existence? In this book, Laurence Mueller and Amitabh Joshi examine current theories of population stability and show how recent laboratory research on model populations--particularly blowflies, Tribolium, and Drosophila--contributes to our understanding of population dynamics and the evolution of stability. The authors review the general theory of population stability and critically analyze techniques for inferring whether a given population is in balance or not. They then show how rigorous empirical research can reveal both the proximal causes of stability (how populations are regulated and maintained at an equilibrium, including the relative roles of biotic and abiotic factors) and its ultimate, mostly evolutionary causes.In the process, they describe experimental studies on model systems that address the effects of age-structure, inbreeding, resource levels, and population structure on the stability and persistence of populations. The discussion incorporates the authors' own findings on the evolution of population stability in Drosophila. They go on to relate laboratory work to studies of animals in the wild and to develop a general framework for relating the life history and ecology of a species to its population dynamics. This accessible, finely written illustration of how carefully designed experiments can improve theory will have tremendous value for all ecologists and evolutionary biologists.

Spatial patterns of movement are fundamental to the ecology of animal populations, influencing their social organization, mating systems, demography, and the spatial distribution of prey and competitors. However, our ability to understand the causes and consequences of animal home range patterns has been limited by the descriptive nature of the statistical models used to analyze them. In Mechanistic Home Range Analysis, Paul Moorcroft and Mark Lewis develop a radically new framework for studying animal home range patterns based on the analysis of correlated random work models for individual movement behavior. They use this framework to develop a series of mechanistic home range models for carnivore populations.The authors' analysis illustrates how, in contrast to traditional statistical home range models that merely describe pattern, mechanistic home range models can be used to discover the underlying ecological determinants of home range patterns observed in populations, make accurate predictions about how spatial distributions of home ranges will change following environmental or demographic disturbance, and analyze the functional significance of the movement strategies of individuals that give rise to observed patterns of space use. By providing researchers and graduate students of ecology and wildlife biology with a more illuminating way to analyze animal movement, Mechanistic Home Range Analysis will be an indispensable reference for years to come.

In a work that will interest researchers in ecology, genetics, botany, entomology, and parasitology, Warren Abrahamson and Arthur Weis present the results of more than twenty-five years of studying plant-insect interactions. Their study centers on the ecology and evolution of interactions among a host plant, the parasitic insect that attacks it, and the suite of insects and birds that are the natural enemies of the parasite. Because this system provides a model that can be subjected to experimental manipulations, it has allowed the authors to address specific theories and concepts that have guided biological research for more than two decades and to engage general problems in evolutionary biology. The specific subjects of research are the host plant goldenrod (Solidago), the parasitic insect Eurosta solidaginis (Diptera: Tephritidae) that induces a gall on the plant stem, and a number of natural enemies of the gallfly. By presenting their detailed empirical studies of the Solidago-Eurosta natural enemy system, the authors demonstrate the complexities of specialized enemy-victim interactions and, thereby, the complex interactive relationships among species more broadly.By utilizing a diverse array of field, laboratory, behavioral, genetic, chemical, and statistical techniques, Abrahamson and Weis present the most thorough study to date of a single system of interacting species. Their interest in the evolutionary ecology of plant-insect interactions leads them to insights on the evolution of species interactions in general. This major work will interest anyone involved in studying the ways in which interdependent species interact.

Spatial Ecology addresses the fundamental effects of space on the dynamics of individual species and on the structure, dynamics, diversity, and stability of multispecies communities. Although the ecological world is unavoidably spatial, there have been few attempts to determine how explicit considerations of space may alter the predictions of ecological models, or what insights it may give into the causes of broad-scale ecological patterns. As this book demonstrates, the spatial structure of a habitat can fundamentally alter both the qualitative and quantitative dynamics and outcomes of ecological processes. Spatial Ecology highlights the importance of space to five topical areas: stability, patterns of diversity, invasions, coexistence, and pattern generation. It illustrates both the diversity of approaches used to study spatial ecology and the underlying similarities of these approaches.Over twenty contributors address issues ranging from the persistence of endangered species, to the maintenance of biodiversity, to the dynamics of hosts and their parasitoids, to disease dynamics, multispecies competition, population genetics, and fundamental processes relevant to all these cases. There have been many recent advances in our understanding of the influence of spatially explicit processes on individual species and on multispecies communities. This book synthesizes these advances, shows the limitations of traditional, non-spatial approaches, and offers a variety of new approaches to spatial ecology that should stimulate ecological research.

Despite its supreme importance and the threat of its global crash, biodiversity remains poorly understood both empirically and theoretically. This ambitious book presents a new, general neutral theory to explain the origin, maintenance, and loss of biodiversity in a biogeographic context. Until now biogeography (the study of the geographic distribution of species) and biodiversity (the study of species richness and relative species abundance) have had largely disjunct intellectual histories. In this book, Stephen Hubbell develops a formal mathematical theory that unifies these two fields. When a speciation process is incorporated into Robert H. MacArthur and Edward O. Wilson's now classical theory of island biogeography, the generalized theory predicts the existence of a universal, dimensionless biodiversity number. In the theory, this fundamental biodiversity number, together with the migration or dispersal rate, completely determines the steady-state distribution of species richness and relative species abundance on local to large geographic spatial scales and short-term to evolutionary time scales.Although neutral, Hubbell's theory is nevertheless able to generate many nonobvious, testable, and remarkably accurate quantitative predictions about biodiversity and biogeography. In many ways Hubbell's theory is the ecological analog to the neutral theory of genetic drift in genetics. The unified neutral theory of biogeography and biodiversity should stimulate research in new theoretical and empirical directions by ecologists, evolutionary biologists, and biogeographers.

Through use of the models Professor Horn has devised, plant ecologists, foresters, and botanists will be able to predict the growth and productivity of a forest, the invading and senile species in a forest, the effect of shade tolerance on forest succession, and similar questions.

In this pathbreaking and far-reaching work George Oster and Edward Wilson provide the first fully developed theory of caste evolution among the social insects. Furthermore, in studying the effects of natural selection in generally increasing the insects' ergonomic efficiency, they go beyond the concentration of previous researchers on the physiological mechanisms of the insects and turn our attention instead to the scale and efficiency of the insects' division of labor. Recognizing that the efficiency of the insect colony is based on a complex fitting of the division of labor to many simultaneous needs, including those imposed by the distribution of resources and enemies around the nest, Professors Oster and Wilson are able to construct a series of mathematical models to characterize the agents of natural selection that promote particular caste systems. The social insects play a key role in the subject of sociobiology because their social organization is so rigid and can be related to genetic evolution. Because of this important consideration, the authors' work has consequences not only for entomology but also for general evolutionary theory.

The modern ecologist usually works in both the field and laboratory, uses statistics and computers, and often works with ecological concepts that are model-based, if not model-driven. How do we make the field and laboratory coherent? How do we link models and data? How do we use statistics to help experimentation? How do we integrate modeling and statistics? How do we confront multiple hypotheses with data and assign degrees of belief to different hypotheses? How do we deal with time series (in which data are linked from one measurement to the next) or put multiple sources of data into one inferential framework? These are the kinds of questions asked and answered by The Ecological Detective. Ray Hilborn and Marc Mangel investigate ecological data much as a detective would investigate a crime scene by trying different hypotheses until a coherent picture emerges. The book is not a set of pat statistical procedures but rather an approach. The Ecological Detective makes liberal use of computer programming for the generation of hypotheses, exploration of data, and the comparison of different models. The authors' attitude is one of exploration, both statistical and graphical.The background required is minimal, so that students with an undergraduate course in statistics and ecology can profitably add this work to their tool-kit for solving ecological problems.

The seemingly innocent observation that the activities of organisms bring about changes in environments is so obvious that it seems an unlikely focus for a new line of thinking about evolution. Yet niche construction--as this process of organism-driven environmental modification is known--has hidden complexities. By transforming biotic and abiotic sources of natural selection in external environments, niche construction generates feedback in evolution on a scale hitherto underestimated--and in a manner that transforms the evolutionary dynamic. It also plays a critical role in ecology, supporting ecosystem engineering and influencing the flow of energy and nutrients through ecosystems. Despite this, niche construction has been given short shrift in theoretical biology, in part because it cannot be fully understood within the framework of standard evolutionary theory. Wedding evolution and ecology, this book extends evolutionary theory by formally including niche construction and ecological inheritance as additional evolutionary processes. The authors support their historic move with empirical data, theoretical population genetics, and conceptual models.They also describe new research methods capable of testing the theory. They demonstrate how their theory can resolve long-standing problems in ecology, particularly by advancing the sorely needed synthesis of ecology and evolution, and how it offers an evolutionary basis for the human sciences. Already hailed as a pioneering work by some of the world's most influential biologists, this is a rare, potentially field-changing contribution to the biological sciences.

Metacommunity ecology links smaller-scale processes that have been the provenance of population and community ecology--such as birth-death processes, species interactions, selection, and stochasticity--with larger-scale issues such as dispersal and habitat heterogeneity. Until now, the field has focused on evaluating the relative importance of distinct processes, with niche-based environmental sorting on one side and neutral-based ecological drift and dispersal limitation on the other. This book moves beyond these artificial categorizations, showing how environmental sorting, dispersal, ecological drift, and other processes influence metacommunity structure simultaneously. Mathew Leibold and Jonathan Chase argue that the relative importance of these processes depends on the characteristics of the organisms, the strengths and types of their interactions, the degree of habitat heterogeneity, the rates of dispersal, and the scale at which the system is observed. Using this synthetic perspective, they explore metacommunity patterns in time and space, including patterns of coexistence, distribution, and diversity.Leibold and Chase demonstrate how these processes and patterns are altered by micro- and macroevolution, traits and phylogenetic relationships, and food web interactions. They then use this scale-explicit perspective to illustrate how metacommunity processes are essential for understanding macroecological and biogeographical patterns as well as ecosystem-level processes. Moving seamlessly across scales and subdisciplines, Metacommunity Ecology is an invaluable reference, one that offers a more integrated approach to ecological patterns and processes.

Can physics be an appropriate framework for the understanding of ecological science? Most ecologists would probably agree that there is little relation between the complexity of natural ecosystems and the simplicity of any example derived from Newtonian physics. Though ecologists have long been interested in concepts originally developed by statistical physicists and later applied to explain everything from why stock markets crash to why rivers develop particular branching patterns, applying such concepts to ecosystems has remained a challenge. Self-Organization in Complex Ecosystems is the first book to clearly synthesize what we have learned about the usefulness of tools from statistical physics in ecology. Ricard Sole and Jordi Bascompte provide a comprehensive introduction to complex systems theory, and ask: do universal laws shape the structure of ecosystems, at least at some scales? They offer the most compelling array of theoretical evidence to date of the potential of nonlinear ecological interactions to generate nonrandom, self-organized patterns at all levels.Tackling classic ecological questions--from population dynamics to biodiversity to macroevolution--the book's novel presentation of theories and data shows the power of statistical physics and complexity in ecology. Self-Organization in Complex Ecosystems will be a staple resource for years to come for ecologists interested in complex systems theory as well as mathematicians and physicists interested in ecology.

Most of the earth's terrestrial species live in the soil. These organisms, which include many thousands of species of fungi and nematodes, shape aboveground plant and animal life as well as our climate and atmosphere. Indeed, all terrestrial ecosystems consist of interdependent aboveground and belowground compartments. Despite this, aboveground and belowground ecology have been conducted largely in isolation. This book represents the first major synthesis to focus explicitly on the connections between aboveground and belowground subsystems--and their importance for community structure and ecosystem functioning. David Wardle integrates a vast body of literature from numerous fields--including population ecology, ecosystem ecology, ecophysiology, ecological theory, soil science, and global-change biology--to explain the key conceptual issues relating to how aboveground and belowground communities affect one another and the processes that each component carries out.He then applies these concepts to a host of critical questions, including the regulation and function of biodiversity as well as the consequences of human-induced global change in the form of biological invasions, extinctions, atmospheric carbon-dioxide enrichment, nitrogen deposition, land-use change, and global warming. Through ambitious theoretical synthesis and a tremendous range of examples, Wardle shows that the key biotic drivers of community and ecosystem properties involve linkages between aboveground and belowground food webs, biotic interaction, the spatial and temporal dynamics of component organisms, and, ultimately, the ecophysiological traits of those organisms that emerge as ecological drivers. His conclusions will propel theoretical and empirical work throughout ecology.

Professor Levins, one of the leading explorers in the field of integrated population biology, considers the mutual interpenetration and joint evolution of organism and environment, occurring on several levels at once. Physiological and behavioral adaptations to short-term fluctuations of the environment condition the responses of populations to long-term changes and geographic gradients. These in turn affect the way species divide the environments among themselves in communities, and, therefore, the numbers of species which can coexist. Environment is treated here abstractly as pattern: patchiness, variability, range, etc. Populations are studied in their patterns: local heterogeneity, geographic variability, faunistic diversity, etc.

To show the importance of stochastic processes in the change of gene frequencies, the authors discuss topics ranging from molecular evolution to two-locus problems in terms of diffusion models. Throughout their discussion, they come to grips with one of the most challenging problems in population genetics--the ways in which genetic variability is maintained in Mendelian populations. R.A. Fisher, J.B.S. Haldane, and Sewall Wright, in pioneering works, confirmed the usefulness of mathematical theory in population genetics. The synthesis their work achieved is recognized today as mathematical genetics, that branch of genetics whose aim is to investigate the laws governing the genetic structure of natural populations and, consequently, to clarify the mechanisms of evolution. For the benefit of population geneticists without advanced mathematical training, Professors Kimura and Ohta use verbal description rather than mathematical symbolism wherever practicable. A mathematical appendix is included.

Most organisms live in a seasonal environment. During their life cycles, some species face seasons of cold and heat, aridity and abundant rainfall, migration and stable residence, breeding and nonbreeding. Populations grow and decline as supplies of materials essential to their survival wax and wane. Such qualitative truths as these flow obviously from field observations. In this original monograph, Stephen Fretwell analyzes the highly complex interaction between a population and a regularly varying environment in an attempt to define and measure seasonality as a critical parameter in the general theory of population regulation. Concerned primarily with the size and the habitat distribution of populations, Professor Fretwell develops simple models that, when applied to specific populations, usually of birds, demonstrate the effect of seasonal variations on the regulation of populations. He maintains that seasonality, as a concept, is essential to a full understanding of environmental interaction.During the course of his exposition, the author offers several new hypotheses, including theories affecting the breeding, numbers, distribution, and diversity of wintering birds, and a theory affecting the body size of sparrows.

Professor Cody's monograph emphasizes the role of competition at levels above single species populations, and describes how competition, by way of the niche concept, determines the structure of communities. Communities may be understood in terms of resource gradients, or niche dimensions, along which species become segregated through competitive interactions. Most communities appear to exist in three or four such dimensions. The first three chapters describe the resource gradients (habitat types, foraging sites, food types), show what factors restrict species to certain parts of the resource gradients and so determine niche breadths, and illustrate the important role of resource predictability in niche overlap between species for resources they share. Most examples are drawn from eleven North and South American bird communities, although the concepts and methodology are far more general.Next, the optimality of community structure is tested through parallel and convergent evolution on different continents with similar climates and habitats, and the direct influence of competitors on resource use is investigated by comparisons of species--poor island communities to species-rich mainland ones. Finally, the author discusses those sorts of environments in which the evolution of one species--one resource set is not achieved, and where alternative schemes of resource allocation, often involving several species that act ecologically as one, must be followed.

This book explores the relationship between various types of reproduction and the evolutionary process. Starting with the concept of meiosis, George C. Williams states the conditions under which an organism with both sexual and asexual reproductive capacities will employ each mode. He argues that in low-fecundity higher organisms, sexual reproduction is generally maladaptive, and persists because there is no ready means of developing an asexual alternative. The book then considers the evolutionary development of diverse forms of sexuality, such as anisogamy, hermaphroditism. and the evolution of differences between males and females in reproductive strategy. The final two chapters examine the effect of genetic recombination on the evolutionary process itself.

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.

Geographic Variation, Speciation and Clines explores the origins and development of geographic variation, divergence, and speciation. In particular it is concerned with genetic divergence as it is usually found on continents, among groups of populations isolated only by distance. Although earlier writers on this topic considered the effects of geography and dispersal, intense geographic differentiation and speciation were thought to require complete isolation. Professor Endler shows how geographic differentiation and speciation may develop in spite of continuous gene flow. Following a review of the diverse and scattered literature on gene flow and population differentiation, the author discusses the relationships among gene flow, dispersal, and migration. He then summarizes the factors which limit the geographic extent of gene flow, and those which allow steep clines to develop in the absence of barriers to gene flow. His analysis draws on examples from the field, experiments, and single- and multiple-locus models. The mechanism and conditions for parapatric speciation are presented: steepening clines, development into hybrid zones, and the evolution of sexual isolation.In the final chapter the author considers the interpretation of natural clines and the associated geographic patterns of subspecies and species.

What is the minimum dimension of a niche space necessary to represent the overlaps among observed niches? This book presents a new technique for obtaining a partial answer to this elementary question about niche space. The author bases his technique on a relation between the combinatorial structure of food webs and the mathematical theory of interval graphs. Professor Cohen collects more than thirty food webs from the ecological literature and analyzes their statistical and combinatorial properties in detail. As a result, he is able to generalize: within habitats of a certain limited physical and temporal heterogeneity, the overlaps among niches, along their trophic (feeding) dimensions, can be represented in a one-dimensional niche space far more often than would be expected by chance alone and perhaps always. This compatibility has not previously been noticed. It indicates that real food webs fall in a small subset of the mathematically possible food webs. Professor Cohen discusses other apparently new features of real food webs, including the constant ratio of the number of kinds of prey to the number of kinds of predators in food webs that describe a community.In conclusion he discusses possible extensions and limitations of his results and suggests directions for future research.

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.

The variety of social systems among the New World blackbirds (Family Icteridae) and the structural simplicity of their foraging environment provide excellent opportunities for testing theorics about the adaptive significance of their behavior. Here Gordon Orians presents the results of his many years of research on how blackbirds utilize their marsh environments during the breeding season. These results stem from information he gathered on three species during ten breeding seasons in the Pacific Northwest, on Red-winged blackbirds during two breeding seasons in Costa Rica, and on three species during one breeding season in Argentina. The author uses models derived from Darwin's theory of natural selection to predict the behavior and morphology of individuals as well as the statistical properties of their populations. First he tests models that predict habitat selection, foraging behavior, territoriality, and mate selection. Then he considers some population patterns, especially range of use of environmental resources and overlap among species, that may result from those individual attributes.Professor Orianns concludes with an overview of the structure of bird communities in marshes of the world and the relation of these patterns to overall source availability in these simple but productive habitats.

In spite of the fact that parasites represent more than half of all living species of plants and animals, their role in the evolution of life on earth has been substantially underestimated. Here, for the first time within an evolutionary and ecological framework, Peter Price integrates the biological attributes that characterize parasites ranging from such diverse groups as viruses, bacteria, protozoa, and fungi, to helminths, mites, insects, and parasitic flowering plants. Synthesizing systematics, ecology, behavioral biology, genetics, and biogeography, the author outlines the success of parasitism as a mode of life, the common features of the wide range of organisms that adopt such a way of life, the reasons for parasites' extraordinary potential for continued adaptive radiation, and their role in molding community structure by means of their impact on the evolution of host species. In demonstrating the importance of parasitic interactions for determining population patterns and geographical distributions, Dr. Price generates further discussion and suggests new areas for research.

One of the central questions of ecology is why there are so many different kinds of plants and animals. Here David Tilman presents a theory of how organisms compete for resources and the way their competition promotes diversity. Developing Hutchinson's suggestion that the main cause of diversity is the feeding relations of species, this book builds a mechanistic, resource-based explanation of the structure and functioning of ecological communities. In a detailed analysis of the Park Grass Experiments at the Rothamsted Experimental Station in England, the author demonstrates that the dramatic results of these 120 years of experimentation are consistent with his theory, as are observations in many other natural communities. The consumer-resource approach of this book is applicable to both animal and plant communities, but the majority of Professor Tilman's discussion concentrates on the structure of plant communities. All theoretical arguments are developed graphically, and formal mathematics is kept to a minimum.The final chapters of the book provide some testable speculations about resources and animal communities and explore such problems as the evolution of "super species," the differences between plant and animal community diversity patterns, and the cause of plant succession.

This book is the first comprehensive treatment of sex allocation from the standpoint of modern evolutionary theory. It shows how the determination of sex ratio, resource allocation to sperm versus egg within simultaneous hermaphroditism, and the evolution of sex reversal can he explained as examples of a single process. The genetical theory, developed mostly with graphical arguments, also specifies when hermaphroditism and dioecy are themselves evolutionary stable. The work balances theory with field and laboratory research, providing critical tests of the theory by empirical studies of sex ratio in parasitoid wasps and mites, sex reversal in shrimp and coral reef fish, and allocation of resources to pollen versus seeds in higher plants. In addition, the author oilers an encyclopedic review of the field and laboratory work of other scientists, reviews many as yet untested hypotheses in sex allocation, and points toward numerous plant and animal systems that hold promise for future tests.

This book maintains that higher plants manifest some degree of sexual selection, and it begins to build a framework that unifies many features of plant reproduction previously considered unrelated. Reviewing evidence for sexual selection in plants, the authors discuss possible male-female interactions, concluding with an extensive set of hypotheses for testing. Mechanisms that could be employed in sexual selection in plants include various cellular mechanisms, such as both nuclear and cytoplasmic genetics, B chromosomes, and paternal contributions to the zygote, as well as abortion, double fertilization, delayed fertilization, and certain forms of polyembryony. This study compares the consequences of these processes for the evolution of mate choice in "gymnosperms" and angiosperms.

Florida Scrub Jays are an excellent example of a cooperative-breeding species, in which adult birds often help raise offspring not their own. For more than a decade Glen E. Woolfenden and John W. Fitzpatrick studied a marked population of these birds in an attempt to establish a demographic base for understanding the phenomenon of "helping at the nest." By studying both population biology and behavior, the authors found that habitat restraints, rather than kin selection, are the main source of the behavior of Florida Scrub Jays: the goal of increasing the number of close relatives other than descendants in future generations is of relatively minor importance in their cooperative-breeding behavior. The Florida Scrub Jay lives only in the Florida oak scrub. All acceptable habitat is constantly filled with breeders. Each year about half of the pairs are assisted by one to several nonbreeding helpers. This book provides extensive data on fecundity, survivorship, relatedness, and dispersal to establish the demographic milieu and to address questions arising out of observed helping behavior--whom, how, when, and why the helpers help.