Showing papers in "Trends in Ecology and Evolution in 1990"

Asymmetric competition in plant populations

Abstract: Recently there has been much interest in the hypothesis that competition between individual plants is asymmetric or onesided: larger individuals obtain a disproportionate share of the resources (for their relative size) and suppress the growth of smaller individuals. This has important implications for population structure, for the analysis of competition between plants at the individual, population and community levels, and for our understanding of competition as a selective force in the evolution of plant populations.

Role of scale and environmental factors in regulation of community structure.

Abstract: Pattern in ecological communities - the distribution, abundance and diversity of species - depends on a complex interplay between large - and local-scale processes. Large-scale variation in factors such as environmental stress, dispersal or productivity sets the stage for local-scale ecological processes such as predation or competition. Until recently, most research focused on local-scale explanations of community pattern. Current models attempt to integrate the role of individual large-scale factors with local-scale processes. This trend will continue, with increased effort to understand the specific means by which large-scale factors cause variation among communities.

Applications of fractals in ecology

Abstract: Fractal models describe the geometry of a wide variety of natural objects such as coastlines, island chains, coral reefs, satellite ocean-color images and patches of vegetation. Cast in the form of modified diffusion models, they can mimic natural and artificial landscapes having different types of complexity of shape. This article provides a brief introduction to fractals and reports on how they can be used by ecologists to answer a variety of basic questions, about scale, measurement and hierarchy in, ecological systems.

The ecology and evolution of reproductive synchrony

Abstract: The temporal pattern of breeding in populations is often characterized by a pronounced temporal clustering of births, flowering or seed set It has long been suspected that this phenomenon is not caused by climatic seasonality alone but that reproductive synchrony represents a strategy that individuals adopt to maximize reproductive success The classical hypotheses predicting an adaptive advantage of reproductive synchrony incorporate both sociobiological and ecological explanations However, new theoretical and empirical analyses have shown that the predicted advantage of reproductive synchrony depends on the ecological setting in which populations reproduce, and processes earlier thought to be responsible only for synchrony may under some ecological conditions lead to asynchronous reproduction being the best strategy

The microevolutionary consequences of climate change

Abstract: Species may respond to climate change by shifting in abundance and distribution, by going extinct, or by evolving Predicting which will occur is difficult Climate change may lead to alterations in both abiotic and biotic components of selection Although there is evidence that abundant genetic variation exists in some species which can respond to such selection, other species seem to have little genetic variation for key characters determining distribution and abundance Moreover, climate change can affect nonselective components of microevolution, such as genetic variances and covariances, and the magnitudes of drift, mutation and gene flow There is almost no species for which we know enough relevant ecology, physiology and genetics to predict its evolutionary response to climate change

The ecology of territoriality in small mammals

Abstract: Recent research on space use and social behavior of small mammals has revealed pronounced differences in the degree of territoriality between species and between sexes within species. Hypotheses to explain these differences have been based on optimality approaches. Leading hypotheses are that the spatial distribution, abundance and renewal rates of food resources determine whether females defend territories, and that the spatial and temporal pattern of availability of females determines whether males are territorial. Other hypotheses invoke resources other than food, or maintain that territoriality in females deters infanticide. This review briefly summarizes these hypotheses and evaluates recently collected evidence from comparative and experimental studies.

Effects of global climate change on the patterns of terrestrial biological communities.

Abstract: Recent paleobiological research has shown that late-Quaternary global warming caused individual species distributions to change along environmental gradients in different directions, at different rates, and over different periods. The individualistic responses of the biota created new community patterns. Individualistic changes can be anticipated in the future and if, as predicted, the rate of warming caused by the ‘greenhouse effect’ is greater than in past events, then the individualistic responses may be even more profound.

Communities as assembled structures: Do rules govern pattern?

Abstract: Because of its unwieldy complexity, understanding organization at the community level has been an elusive, often frustrating enterprise. This survey concentrates on the assembly process itself, and examines whether there are mechanics to community assembly that provide the foundation for a general theory of organization at the community level.

Herbivory simulations in ecological research.

Abstract: Because of the experimental advantages that they offer, mechanical simulations of grazing are more commonly used than true herbivory in ecological studies of the impact of herbivory on plants. However, few studies have explicitly compared plant responses to herbivory and to mechanical simulations. Most such comparisons report differences in plant responses to mechanical versus true herbivory, even though the amounts and types of tissue removed were similar. Moreover, studies that also attempted to mimic the timing of leaf damage report differences in plant responses to the different damage modes. Because a plant's response to herbivory is complex and is activated by more than merely the removal of tissue, exact mechanical simulations may prove difficult.

Monogamy and long-term pair bonding in vertebrates.

Abstract: The term 'monogamy' represents a complex of mating systems that has been relalively neglected. Monogamy is generally associated with significant biparental care and is most common among birds. Recent work has addressed such aspects as the evolutionary incentives for (and value of) contributions by the male parent, how the distributions of females and critical nesting resources can promote monogamy, male defense of genetic paternity, the causes of long-term mate-retention in certain species, and the subtle means by which sexual selection operates within basically monogamous systems. New advances in testing genetic relatedness, especially DNA fingerprinting, promise much for the assessment of individual costs and benefits of monogamy.

Evolutionary dynamics of a natural population: The large cactus finch of the galapagos

Abstract: Presents a careful account of the results of a research project which began in 1973 and ran continuously for eleven years. Treats the ecology, behavior and genetics of a population still resident where it evolved, and small enough to permit the identification of every individual. Beautifully produce

Evolution of diversity at the major histocompatibility complex

Abstract: Recent evidence from both population data and DNA sequence analyses indicates that the unprecedented genetic diversity found at MHC loci is selectively maintained in contemporary natural populations, although the strength and nature of this selection are currently unclear. Due to the critical role played by MHC molecules in immune recognition, it is generally assumed that some form of parasite-driven selection is operating. However, the general failure to implicate MHC in the susceptibility to specific infectious diseases has been troubling, and may indicate that selection is too weak to detect directly. Alternatively, strong selection can be reconciled by a variety of factors including the amplification of minor (disease-based) vigor differences into large fitness differences by intraspecific competition, or non-disease-based selection such as mating preferences and selective abortion.

Parasite-host coevolution

Abstract: Parasite—host coevolution can have many different endpoints, not simply the commensalism of ‘conventional wisdom'. Empirical studies and mathematical models are elucidating the conditions under which parasite—host systems can coevolve to intermediate and high levels of parasite virulence — and when they can coevolve to commensalism and mutualism.

Mechanisms of sperm competition.

Abstract: Sperm competition occurs when two (or more) males inseminate a single female during a reproductive cycle, but what determines which one of them will fertilize her eggs? Is it simply a lottery, or are there some more complex rules by which matings are translated into offspring? Several studies covering various animal groups have shown that mating order effects are often important in determining paternity patterns: in animals as different as insects and birds, the sperm from the last male to mate often has precedence over previously introduced sperm. Recently, behavioural ecologists and physiologists have started to examine the mechanisms by which sperm precedence is achieved. The study of sperm competition mechanisms complements the more behavioural studies, and a combination of the two approaches used on single species should prove to be particularly rewarding.

Coral reef primary productivity. A hierarchy of pattern and process

Abstract: The abundance of interdisciplinary studies of coral reef metabolism means that coral reefs are amongst the best understood of marine benthic communities in terms of the determinants of primary production and nutrient fluxes, and their variation, at different levels of integration. Recent work has extended our understanding of the variation in coral reef productivity at different spatial and temporal scales. Nutrient limitation of production at scales ranging from the organism to the ecosystem is one of the most important topics of research at present, the relevance of which extends well beyond the tropics.

Hypotheses for the evolution of dioecy in seed plants

Abstract: Over the last decade, new hypotheses have been proposed for the evolution of dioecy in plants. Most of the selective mechanisms invoked have been suggested and supported by phylogenetic correlations. Here we review (1) the validity of the correlations (especially in light of recent critiques of the comparative method), and (2) the conformity of the proposed mechanisms to empirical data. None of the hypotheses can be flatly rejected on existing evidence, but the strength of their support varies. Future correlational studies must explicitly consider phylogeny; more importantly, such broad studies should also be supplemented by detailed studies of particular transitions to dioecy (e.g. within genera) — studies of the sort that have clarified analogous issues such as heterostyly.

Increased genetic variance after a population bottleneck

Abstract: A conventional view holds that population bottlenecks cause massive losses of genetic variability, thus endangering the viability of the derived population. Although some alleles that were infrequent in the parent population may be lost new empirical evidence from Drosophila and housefly populations has demonstrated that genetic variance available to selection may actually increase following a single severe bottleneck. Several theoretical models support this view, and suggest that the increase may result from conversion of balanced epistatic variance to additive variance that becomes immediately available to selection. These effects appear to be greatest on the inheritance of quantitative characters, releasing new variance through the disruption of covariance matrices that underlie and interrelate quantitative traits. Thus, character change in adaptation and speciation may, in some instances, be promoted by founder events.

Choice of colony size in birds

Abstract: Most populations of colonial birds exhibit extensive variation in colony size. Field studies over the last decade have shown that individual birds breeding in colonies of certain sizes are apparently more successful than those settling in colonies of other sizes, yet size variation persists. Enough information is now available to suggest four explanations for how birds choose colonies and why colonies vary in size.

Evaluation of natural enemies for biological control: A behavioral approach

Abstract: The success of biological pest control has stimulated the development of analytical models that explore the dynamics of natural enemies and their hosts or prey. These models seek to identify those general characteristics o f the natural enemy, host or prey population that lead to economic pest control. Because the models are strategic in nature, they are of limited value in identifying the specific attributes of an effective biological control agent prior to its introduction. Empirically developed criteria have also been of limited predictive value because they too provide only general guidelines. Behavioral ecology and foraging and sexratio theories may be useful adjuncts to these approaches, by identifying the evolutionary constraints and thus helping to define better the attributes of an effective natural enemy.

The genetics of transient populations: Research at the metapopulation level

Abstract: The metapopulation concept allows us to generate new models, in which each single local population is in disequilibrium (from both demographic and genetic points of view) but the whole is stable. We review recent empirical and theoretical results showing the relevance of the metapopulation level, in particular for understanding the evolution of those traits that do not experience the same selective forces during the different demographic stages of each local population.

Competition within and between encrusting clonal invertebrates

Abstract: Colonies of encrusting marine invertebrates are tractable models for the study of competition, because of the relative ease with which observations can be made on the frequency and outcome of overgrowth interactions. Studies of intraspecific competition have found that competition is predicated upon a genetically controlled recognition event, which results in either fusion or rejection. Data are rapidly accumulating in two model systems showing that fusion is associated with somatic cell parasitism and that rejection is associated with overgrowth. Thus, encounters between conspecifics define a choice: to compete at the level of the cell lineage or to compete at the level of the colony. Fusion-rejection genes act to control the units (or targets) of selection.

Ecology of a simple plant-herbivore system: biological control of Salvinia.

Abstract: The salvinia-herbivore system has been investigated in more detail than most, because of its relative simplicity due to the absence o f sexual and dormant stages in the plant's life cycle, the apparent genetic uniformity of the plant, the absence of water stress, the uniformity of the water surface habitat and the absence of herbivores outside the plant's native range. This review describes how biological control of salvinia was achieved and discusses ecological principles illustrated by salvinia and its herbivores.

Monospecific dominance in tropical rain forests.

Abstract: Old-growth rain forests that are dominated by a single canopy species occur throughout the tropics, though they account for a limited proportion of the total rain forest area. These forests have been considered anomalies in which development of a more diverse community is deflected by harsh conditions. Very poor soils or an otherwise extreme environment may promote monodominance by excluding potentially competing species, but it is now apparent that monodominant tropical forests also develop under more benign conditions. Field studies have shown that a single species may dominate on undisturbed sites where the soils are similar to those of adjacent old-growth, mixed forests. In these situations the dominant is a superior competitor and/or is particularly tolerant to stresses such as shade. Assertion of dominance by a single species in an old-growth forest appears most likely in areas where the species pool contains few late-succession species with similar life history traits.

Inducible defenses, phenotypic variability and biotic environments

Abstract: Defensive morphologies, chemicals and behaviors induced by cues from consumers or competitors have been described in numerous organisms. Much work has focused on the costs of defenses and the actual cues used. Here, we review recent progress in determining the effects of inducible defenses on consumers and the cues implicated in inducing defenses against consumers and competitors, thereby laying the groundwork for studying the implications of inducible defenses for the dynamics of foraging, population size and evolution.