Resource Competition And Community Structure Mpb 17 Volume 17

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.

Whether in felling trees for wood, rearing insects for biological control, or culling animals for conservation purposes, efficient management of biological systems requires quantitative analysis of population growth and harvesting policies. Aiming to encourage the exchange of ideas among scientists involved in the management of fisheries, wildlife, forest stands, and pest control, the authors of this work present a general framework for modeling populations that reproduce seasonally and that have age or stage structure as an essential component of management strategy. The book represents the first time that examples from such diverse areas of biological resource management have been brought together in a unified modeling framework using the standard notation of mathematical systems theory. In addition, the authors combine a nonlinear extension of Leslie matrix theory and certain linear elements, thereby permitting interesting analytical results and the creation of compact, realistic simulation models of resource systems.

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.

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.

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.

A common tendency in the field of population ecology has been to overlook individual differences by treating populations as homogeneous units; conversely, in behavioral ecology the tendency has been to concentrate on how individual behavior is shaped by evolutionary forces, but not on how this behavior affects population dynamics. Adam Lomnicki and others aim to remedy this one-sidedness by showing that the overall dynamical behavior of populations must ultimately be understood in terms of the behavior of individuals. Professor Lomnicki's wide-ranging presentation of this approach includes simple mathematical models aimed at describing both the origin and consequences of individual variation among plants and animals. The author contends that further progress in population ecology will require taking into account individual differences other than sex, age, and taxonomic affiliation--unequal access to resources, for instance. Population ecologists who adopt this viewpoint may discover new answers to classical questions of population ecology. Partly because it uses a variety of examples from many taxonomic groups, this work will appeal not only to population ecologists but to ecologists in general.

Natural selection is an immense and important subject, yet there have been few attempts to summarize its effects on natural populations, and fewer still which discuss the problems of working with natural selection in the wild. These are the purposes of John Endler's book. In it, he discusses the methods and problems involved in the demonstration and measurement of natural selection, presents the critical evidence for its existence, and places it in an evolutionary perspective. Professor Endler finds that there are a remarkable number of direct demonstrations of selection in a wide variety of animals and plants. The distribution of observed magnitudes of selection in natural populations is surprisingly broad, and it overlaps extensively the range of values found in artificial selection. He argues that the common assumption that selection is usually weak in natural populations is no longer tenable, but that natural selection is only one component of the process of evolution; natural selection can explain the change of frequencies of variants, but not their origins.