Showing papers in "Trends in Ecology and Evolution in 1991"

Predation risk as a cost of reproduction.

Abstract: Predation risk as a cost of reproduction in animals has recently received increased empirical and theoretical attention. Higher risk may be associated with all stages of reproduction. Examples of evolutionary responses to this increased risk include habitat choice, duration and timing of display and copulation, changes in brightness of breeding coloration, and changes in life history traits such as age of reproduction and reproductive effort.

Climate change and the evolution of C4 photosynthesis

Abstract: Plants assimilate carbon by one of three photosynthetic pathways, commonly called the C 3 , C 4 , and CAM pathways The C 4 photosynthetic pathway, found only among the angiosperms, represents a modification of C 3 metabolism that is most effective at low concentrations of CO 2 Today, C 4 plants are most common in hot, open ecosystems, and it is commonly felt that they evolved under these conditions However, high light and high temperature, by themselves, are not sufficient to favor the evolution of C 4 photosynthesis at atmospheric CO 2 levels significantly above the current ambient values A review of evidence suggests that C 4 plants evolved in response to a reduction in atmospheric CO 2 levels that began during the Cretaceous and continued until the Miocene

Indirect effects in community ecology: Their definition, study and importance.

Abstract: The diversity of indirect interactions that can occur within communities is large. Recent research on indirect interactions is scattered in the literature under numerous labels. The definition of indirect effects is an important aspect of their study, and clarifies some of the subtle differences among indirect effects found in natural communities. Choosing which species to study, how to manipulate species and for what duration, which attributes to measure and, finally, which analytical techniques to use are all problems facing the community ecologist. Ultimately, we are striving for the best means of determining the relative importance of direct and indirect effects in structuring communities.

Coral reef bleaching in the 1980s and possible connections with global warming.

Abstract: Scleractinian corals and their symbiotic dinoflagellate algae build massive, wave-resistant coral reefs that are pre-eminent in shallow tropical seas. This mutualism is especially sensitive to numerous environmental stresses, and has been disrupted frequently during the past decade. Increased seawater temperatures have been proposed as the most likely cause of coral reef bleaching, and it has been suggested that the recent large-scale disturbances are the first biological indication of global warming. This article describes recent bleaching events and their possible link with sea warming and other environmental stresses, and offers some speculation on the fate of coral reefs if the Earth enters a sustained period of warming.

Phenotypic plasticity as a component of evolutionary change.

Abstract: Phenotypic plasticity has often been assumed to buffer the effects of natural selection and thus act as a constraint on evolutionary change. It has become increasingly clear, however, that phenotypic plasticity actually represents a fundamental component of evolutionary change. Where genetic variation for plasticity exists, a population with a different mean plasticity can evolve. Recent attention has been focused on the conditions necessary for the evolution of phenotypic plasticity, i.e. those under which a generalist strategy, as opposed to a range of genetically differentiated specialists, will be favoured. It is also now clear that genotypes that perform best in one environment usually perform less well than other genotypes in a different environment; hence, their greater response is not an adaptation to environmental variation. A response to environmental variation is only adaptive if it represents a mechanism by which relative fitness is maintained in the face of environmental variation. Adaptive plasticity may thus involve both physiological homeostasis and morphological response.

Parasitism: A cryptic determinant of animal community structure.

Abstract: Traditionally, the major biotic determinants of animal community structure were assumed to be competition and predation. Recent theoretical, experimental and field studies indicate that parasitism is also important. The spectrum of effects that parasites have on host individuals is as broad as the range of parasite-host interactions. This review considers evidence for direct effects of parasites on fecundity and survival that influence host demography, and for indirect effects on host physiology and behavior that interface with competition and predation.

Theories of sexual selection.

Abstract: Recent research on sexual selection in animals has begun to indicate that ‘handicaps' and ‘honest signalling' may play more important roles than hitherto thought. This review reappraises theories of sexual selection in the light of these new developments.

Phylogenetic studies of insect-plant interactions: Insights into the genesis of diversity

Abstract: Phylogenetic analyses (and related historical evidence) can be used to test hypotheses about the oppurtinity for coevolution among plants and insect herbivores, the role of plant chemistry in mediating host shifts, the reality of coevolutionary ‘arms races', and the role of novel defensive or counterdefensive characteristics in enhancing rates of diversification. Recent analyses provide evidence on each of these hypotheses. The strong phylogenetic component in many insect-plant associations suggests that host shifts by insects are often strongly constrained, that insect diets may not be ‘optimal', and that the trophic structure and species diversity of local communities strongly reflect evolutionary history.

A need for niches

Abstract: The idea that different species must have distinct ecologies if they are to coexist has been challenged recently by the claim that some models involving stochastic factors or clumped spatial distributions permit stable coexistence of species that are identical or differ only in competitive ability. However, these models have been misinterpreted; except in rather limited circumstances, they provide further support for the notion that species must be sufficiently ecologically distinct to coexist stably. The possible, limited, exceptions to this rule involve social factors by which individuals of a species discriminate between heterospecifics and conspecifics without there being any true ecological differences between species.

Spatial patterns in soft-bottom communities

Abstract: The spatial patterns exhibited by soft-bottom macrobenthic organismshave become recognized for their potential to play an importantrole in determining both the ecology of these species and our ability to study it. Recent studies have shown that spatial scales of field sampling or experimentation are important influences on data interpretation. The presence of patches, density gradients and spatially autocorrelated variables may confound designs and affect the validity of inferential statistics. Future studies must integrate the intensity and form of patterns from various spatial and temporal scales if we are to understand the process responsible for generating pattern.

Path analyses of selection

Abstract: Identifying the targets and causal mechanisms of phenotypic selection in natural populations remains an important challenge for evolutionary biologists. Path analysis is a statistical modeling approach that may aid in meeting this challenge. We describe several types of path model that are relevant to the analysis of selection, and review some recent empirical studies that apply path models to issues in pollination biology, phenotypic integration and selection on morphometric and ontogenetic traits. Path analysis may play two roles in the analysis of selection: first, as an exploratory analysis suggesting possible targets of selection, which are then tested by direct experimentation; and second, as a means of evaluating the relative importance of different causal pathways of selection, once the likely targets of selection have been established.

Genetic consequences of local population extinction and recolonization.

Abstract: Theoretical results have shown that a pattern of local extinction and recolonization can have significant consequences for the genetic structure of subdivided populations; consequences that are relevant to issues in both evolutionary and conservation biology. The nature of those consequences depends largely on the mode of colony formation. Extinction and recolonization can either increase or decrease the genetic differentiation of local populations and can lead to a loss of the genetic diversity stored in an array of populations. Recent ecological studies of two insect species have revealed population structures resembling, in part, that considered in the models. They serve to illustrate the potential complexity of the processes of extinction and recolonizatiion in nature.

The effects of phenotypic plasticity on genetic correlations

Abstract: Recent theory suggests that genetic correlations should help to predict the simultaneous response to selection of two or more traits, and much recent research has been directed towards understanding the sources of variation in genetic correlations. Genetic correlations can change from sample to sample, from species to species, from population to population, during the course of development and — within a population, at a fixed stage of development — from one environment to another. These are changes not only in magnitude but also in sign. Theory suggests that genetic correlations should not change sign when the two traits are tightly integrated by physiology or development. Patterns of change of genetic correlations are caused by differences in development and physiology, an understanding of which appears to be necessary to predict the response to selection in natural, heterogeneous environments.

Pursuit-deterrent signals: communication between prey and predator.

Abstract: When encountering predators, prey animals often expose themselves by loud vocalization, by repeated movements or by revealing conspicuous colors. The more elaborate displays were often considered to be warning signals directed to other prey, and the less obvious displays to be intention movements. During the last decade, there has been increasing evidence that, in fact, prey display is aimed at the predator, apparently to deter further pursuit. This communication between two seemingly unlikely partners, prey and predator, appears to be based upon a common interest — satisfying the predator's need for further information.

Resource capture, biomass allocation and growth in herbaceous plants

Abstract: Plant species differ widely in their rate of biomass production, even when grown under optimal conditions. A key question concerns the extent to which these growth rates correlate with the uptake of carbon and nitrogen and with the biomass allocation between leaves and roots. Recent data show that the answer to this question differs for mono- and dicotyledons, and that more than biomass allocation, it is the ratio between the activities of leaves and roots that correlates with the growth rate of a plant.

Sexual competition among females: What causes courtship-role reversal?

Abstract: In most animals, males are the competitive sex whereas females are typically non-competitive and choosy of mates. In a variety of taxa, certain species (or populations within species) show a reversal in these typical courtship roles. Recent research with these organisms supports a central tenet of sexual selection theory: that it is the relative investment of the sexes in offspring that controls the number of males and females available for mating, and thus is the main determinant of the degree of sexual competition in each sex.

Laying eggs in others' nests: Intraspecific brood parasitism in birds

Abstract: Intraspecific brood parasitism occurs commonly in a large number of bird species. Recent work shows that females parasitize the parental care of conspecifics either as a ‘best-of-a-bad-job' strategy or as part of a superior reproductive strategy. A number of parasite and host behaviours, which either facilitate or prevent intraspecific brood parasitism, are similar to those occurring among interspecific brood parasites and their hosts.

SINEs: Short interspersed repeated elements of the eukaryotic genome

Abstract: Much of the eukaryotic genome is composed of a variety of repetitive sequences. Amongst these, there are two kinds of retroposons (sequence elements derived from nonviral cellular RNA): SINEs (short interspersed elements) and LINEs (long interspersed elements). Amplification of SINEs occurs in a single germ cell, and the members of SINEs spread and become fixed in populations through genetic drift. SINEs can be regarded as phylogenetic landmarks: they are specific to one species, a few species, a genus or in some cases a family, indicating a specific time of amplification during evolution. Recent studies concerning the structure and origin of many SINEs revealed that retroposons are more widespread in animal genomes than was previously thought.

The evolution of developmental strategy in marine invertebrates

Abstract: Developmental mode varies widely in most animal phyla. These differences in developmental strategy exert a profound influence on the ecology and evolution of closely related species. The mechanistic alterations in ontogeny that lead to switches in developmental mode are coming under increasing scrutiny. Echinoids are one of the best-understood groups in this regard. Parallel modifications in direct-developing echinoids point to some of the key changes in oogenesis and embryogenesis that produce switches in developmental mode.

Cryptic dioecy in flowering plants

Abstract: In some dioecious plant species, mates and/or females have large and presumably costly opposite-sex structures that are sterile. This is termed 'cryptic dioecy'. Several new cases of cryptic dioecy have recently been studied. They may give information about the minimal requirements for the evolution of separate sexes from hermaphroditism, because the most important differences contributing to the initial advantage of the breeding system have not been obscured by further developments. Reviewed in this light, cryptic dioecy can provide evidence on the role of reallocation of reproductive resources in the evolution of dioecy.

Behavioral ecology of larval dragonflies and damselflies

Abstract: During the past decade, larval dragonflies and damselflies (Insecta: Odonata) have been the subjects for very productive ecological research. Descriptive field work, enclosure experiments and laboratory behavior studies have identified fish predation, intraguild predation (especially mutual predation among odonates, including cannibalism) and interference competition as particularly strong interactions influencing larval odonate assemblages. Behavioral differences among species suggest evolutionary adaptations for coexistence with different predators, and for winning intraspecific aggressive encounters.