Showing papers in "Trends in Ecology and Evolution in 1996"
TL;DR: Viewing an individual's immune response to parasites as being subject to optimization in the face of other demands offers potential insights into mechanisms of life history trade-offs, sexual selection, parasite-mediated selection and population dynamics.
Abstract: In the face of continuous threats from parasites, hosts have evolved an elaborate series of preventative and controlling measures - the immune system - in order to reduce the fitness costs of parasitism. However, these measures do have associated costs. Viewing an individual's immune response to parasites as being subject to optimization in the face of other demands offers potential insights into mechanisms of life history trade-offs, sexual selection, parasite-mediated selection and population dynamics. We discuss some recent results that have been obtained by practitioners of this approach in natural and semi-natural populations, and suggest some ways in which this field may progress in the near future.
2,405 citations
TL;DR: Results of recent empirical studies suggest that while genetic variation may decrease with reduced remnant population size, not all fragmentation events lead to genetic losses and different types of genetic variation (e.g. allozyme and quantitative variation) may respond differently.
Abstract: Habitat fragmentation reduces the size and increases the spatial isolation of plant populations. Initial predictions have been that such changes will be accompanied by an erosion of genetic variation and increased interpopulation genetic divergence due to increased random genetic drift, elevated inbreeding and reduced gene flow. Results of recent empirical studies suggest that while genetic variation may decrease with reduced remnant population size, not all fragmentation events lead to genetic losses and different types of genetic variation (e.g. allozyme and quantitative variation) may respond differently. In some circumstances, fragmentation actually appears to increase gene flow among remnant populations, breaking down local genetic structure.
1,941 citations
TL;DR: Interspecific studies show that microsatellites are poor markers for phylogenetic inference, however, these studies are fuelling discussions on directional mutation and the role of selection and recombination in their evolution, Nonetheless, it remains true that microSatellites may be considered as good, neutral mendelian markers.
Abstract: Population genetics studies using microsatellites, and data on their molecular dynamics, are on the increase. But, so far, no consensus has emerged on which mutation model should be used, though this is of paramount importance for analysis of population genetic structure. However, this is not surprising given the variety of microsatellite molecular motifs. Null alleles may be disturbing for population studies, even though their presence can be detected through careful population analyses, while homoplasy seems of little concern, at least over short evolutionary scales. Interspecific studies show that microsatellites are poor markers for phylogenetic inference. However, these studies are fuelling discussions on directional mutation and the role of selection and recombination in their evolution. Nonetheless, it remains true that microsatellites may be considered as good, neutral mendelian markers.
1,619 citations
TL;DR: Recent findings suggest that almost all alternative reproductive phenotypes within the sexes are due to alternative tactics within a conditional strategy, and, as such, while the average fitnesses of the alternative phenotypes are unequal, the strategy is favoured in evolution.
Abstract: theoretical framework, the concept of the mixed strategy has not been realized in nature, and alternative strategies are very rare. Recent findings suggest that almost all alternative reproductive phenotypes within the sexes are due to alternative tactics within a conditional strategy, and, as such, while the average fitnesses of the alternative phenotypes are unequal, the strategy is favoured in evolution. Proximate mechanisms that underlie alternative phenotypes may have many similarities with those operating between the sexes.
1,582 citations
TL;DR: Analysis of reliable methods for studying rate variation shows that failure to account for rate variation can have drastic effects, leading to biased dating of speciation events, biased estimation of the transition:transversion rate ratio, and incorrect reconstruction of phylogenies.
Abstract: Although several decades of study have revealed the ubiquity of variation of evolutionary rates among sites, reliable methods for studying rate variation were not developed until very recently. Early methods fit theoretical distributions to the numbers of changes at sites inferred by parsimony and substantially underestimate the rate variation. Recent analyses show that failure to account for rate variation can have drastic effects, leading to biased dating of speciation events, biased estimation of the transition:transversion rate ratio, and incorrect reconstruction of phylogenies.
1,179 citations
TL;DR: Recent evidence for inbreeding depression under natural conditions is summarized, inbreeding avoidance mechanisms are reviewed, and the idea that animals have evolved mechanisms to avoid outbreeding is examined.
Abstract: The phenomenon of inbreeding depression is well documented and behavioral adaptations for inbreeding avoidance have been described. However, there is debate over whether inbreeding depression is always an important selective force on behavior. Here, we summarize recent evidence for inbreeding depression under natural conditions, review inbreeding avoidance mechanisms, and discuss how these are influenced by social structure. We also examine the idea that animals have evolved mechanisms to avoid outbreeding.
985 citations
TL;DR: The high plant diversity of mediterranean-climate regions has attracted much attention over the past few years as mentioned in this paper, and a review discusses patterns and determinants of local, differential and regional plant diversity in all five regions.
Abstract: The high plant diversity of mediterranean-climate regions has attracted much attention over the past few years. This review discusses patterns and determinants of local, differential and regional plant diversity in all five regions. Local diversity shows great variation within and between regions and explanations for these patterns invoke a wide range of hypotheses. Patterns of regional diversity are the result of differential speciation and extinction rates during the Quaternary. These rates have been influenced more by the incidence of fire and the severity of climate change than by environmental heterogeneity. All regions have a high number of rare and locally endemic taxa that survive as small populations, many of which are threatened by habitat transformation.
927 citations
TL;DR: A landscape-conscious behavioral undertaking would not only establish more firmly the link between behavior and ecological systems, but also catalyze the study of basic biological phenomena of Interest to behaviorists and ecologists alike.
Abstract: Recent developments in landscape-level ecological modeling rest upon poorly understood behavioral phenomena. Surprisingly, these phenomena include animal movement and habitat selection, two areas with a long history of study in behavioral ecology. A major problem in applying traditional behavioral ecology to landscape-level ecological problems is that ecologists and behaviorists work at very different spatial scales. Thus a behavioral ecology of ecological landscapes would strive to overcome this inopportune differential in spatial scales. Such a landscape-conscious behavioral undertaking would not only establish more firmly the link between behavior and ecological systems, but also catalyze the study of basic biological phenomena of Interest to behaviorists and ecologists alike.
908 citations
TL;DR: A better understanding of how the nuclear sequences themselves are interesting, and capable of serving as valuable molecular tools, they can also confound phylogenetic and population genetic studies.
Abstract: The combined use of mitochondrial DNA markers and polymerase chain reaction (PCR) techniques has greatly enhanced evolutionary studies. These techniques have also promoted the discovery of mitochondrial-like sequences in the nuclear genomes of many animals. While the nuclear sequences themselves are interesting, and capable of serving as valuable molecular tools, they can also confound phylogenetic and population genetic studies. Clearly, a better understanding of these phenomena and vigilance towards misleading data are needed.
888 citations
TL;DR: Some of the advantages and disadvantages of the different approaches for the treatment of partitioned data are reviewed, with special concentration on which methods help to discern the evolutionary process and provide the most accurate estimates of phylogeny.
Abstract: Systematists have access to multiple sources of character information in phylogenetic analysis. For example, it is not unusual to have nucleotide sequences from several different genes, or to have molecular and morphological data. How should diverse data be analyzed in phylogenetic analysis? Several methods have been proposed for the treatment of partitioned data: the total evidence, separate analysis, and conditional combination approaches. Here, we review some of the advantages and disadvantages of the different approaches, with special concentration on which methods help us to discern the evolutionary process and provide the most accurate estimates of phylogeny.
852 citations
TL;DR: The study of human sexuality from the darwinian perspective is in an explosive phase, and recent research reveals that the sexual selection that designed human secondary sexual traits was functional rather than strictly fisherian.
Abstract: The study of human sexuality from the darwinian perspective is in an explosive phase. Recent research is diverse; for instance, the dynamics of heterosexual relationships, the role of honest advertisement in attractiveness, the role of fluctuating asymmetry in sexual competition, and sexual conflict over fertilization, seen in sperm competition adaptations of men and possible cryptic sire-choice adaptation of women. Also, recent research reveals that the sexual selection that designed human secondary sexual traits was functional rather than strictly fisherian.
TL;DR: This work states that within a landscape, a permanent migration of propagules or individuals from source to sink habitats may lead to a stabilization of the overall demographic system, and this simple situation, explored in the recent literature, has surprising properties.
Abstract: The various habitats inhabited by a given species are never of the same quality. When demographic models take into account this habitat heterogeneity, the source-sink concept naturally emerges: a local demographic surplus arises in good quality habitats (source), and a local demographic deficit occurs in habitats of poor quality (sink). Within a landscape, a permanent migration of propagules or individuals from source to sink habitats may lead to a stabilization of the overall demographic system. This simple situation, explored in the recent literature, has surprising properties. In particular, it requires a change in our view of classical concepts such as ecological niche and carrying capacity, it can explain the existence and persistence of local maladaptation and it can improve conservation practice.
TL;DR: A more focused, functional approach to the study of forest fragmentation is required to move beyond the description of pattern and to determine how changes in insect communities affect ecosystem processes in fragmented forests.
Abstract: Insects are highly susceptible to the adverse effects of forest fragmentation. It is now beyond any doubt that fragmentation-induced changes in abundance and species richness occur in many insect groups. However, the study of insects in fragmented forests is still in its infancy and lacks real direction. Simple empirical studies are not answering the questions we most want to answer about fragmented systems. Are we in the midst of a mass-extinction crisis? What is the functional significance of the immense insect biodiversity? Does biodiversity loss affect ecosystem functioning? A more focused, functional approach to the study of forest fragmentation is required to move beyond the description of pattern and to determine how changes in insect communities affect ecosystem processes in fragmented forests.
TL;DR: The inadequacy of dispersal data obtained directly by traditional methods using population studies of marked individuals is highlighted by comparing the resulting distributions with dispersal estimates obtained by radio-tracking and by using genetic estimates of gene flow.
Abstract: Dispersal is of central importance to population biology, behavioral ecology and conservation. However, because field studies are based on finite study areas, nearly all dispersal distributions for vertebrates currently available are biased, often highly so. The inadequacy of dispersal data obtained directly by traditional methods using population studies of marked individuals is highlighted by comparing the resulting distributions with dispersal estimates obtained by radio-tracking and by using genetic estimates of gene flow.
TL;DR: The original role of parental investment in predicting sexual selection has recently been complemented by the use of sexual differences in potential reproductive rates (PRR) and the concept of OSR is explored.
Abstract: In sexually reproducing animals, individuals of one sex may have to compete for access to mating partners of the opposite sex. The operational sex ratio (OSR) is central in predicting the intensity of mating competition and which sex is competing for which. Thanks to recent theoretical and empirical advances, particularly by exploring the concept of OSR, sexual selection studies today are becoming more fine-tuned and dynamic. The original role of parental investment in predicting sexual selection has recently been complemented by the use of sexual differences in potential reproductive rates (PRR).
TL;DR: In areas with little rain forest remaining, fragments can be the 'seeds' from which to re-establish extensive forest and become the last refuges of many rainforest species that are on the brink of extinction.
Abstract: Deforestation is occurring at an alarming rate in the lowland tropics. In many tropical regions, rain forest is restricted to small (
TL;DR: Empirical and modeling studies reveal that mechanisms (2 and 3) are largely responsible for age-related decline in ANPP for forests in cold environments and increasing respiratory costs appear to be relatively unimportant in explaining declining productivity in ageing stands.
Abstract: Aboveground net primary production (ANPP) commonly reaches a maximum in young forest stands and decreases by 0-76% as stands mature. However, the mechanism(s) responsible for the decline are not well understood. Current hypotheses for declining ANPP with stand age include: (1) an altered balance between photosynthetic and respiring tissues, (2) decreasing soil nutrient availability, and (3) increasing stomatal limitation leading to reduced photosynthetic rates. Recent empirical and modeling studies reveal that mechanisms (2) and (3) are largely responsible for age-related decline in ANPP for forests in cold environments. Increasing respiratory costs appear to be relatively unimportant in explaining declining productivity in ageing stands.
TL;DR: A longer-term view indicates that the causes of change in neotropical secondary successions are similar to those operating in temperate forests, but yields sobering conclusions for conservation.
Abstract: More and more areas of deforested wet tropical lands are being handed back to nature as their erstwhile owners abandon attempts to farm them. The resulting secondary successions offer hope that some of the unique characteristics of the original rain forests may be recovered and conserved. However, most of our understanding of what secondary tropical rain forests are and how and why they develop is limited to the first decade of a process that may last for centuries. A longer-term view indicates that the causes of change in neotropical secondary successions are similar to those operating in temperate forests, but yields sobering conclusions for conservation.
TL;DR: Although ancient asexuals challenge current theories of sex, understanding how they manage to persist will help to explain why most organisms are sexual.
Abstract: Asexual organisms that are descended from ancient asexual lineages defy current thinking on the evolution of sexual reproduction; theoreticians have been anxious to explain away their existence. However, a number of groups of organisms, from ferns to rotifers, have been suggested to be anciently asexual, and favourable evidence is being accumulated. Furthermore, new techniques for assessing claims of ancient asexuality have been proposed. Although ancient asexuals challenge current theories of sex, understanding how they manage to persist will help to explain why most organisms are sexual.
TL;DR: Current experiments aim to unravel the adaptive mechanisms whereby terrestrial plants cope with the peculiar conditions of the floodplain, from the whole plant down to the cell.
Abstract: Floodplains and wetlands are highly suitable for plant ecological studies, whether for agricultural interests, nature conservation or basic science. Traditional work has entailed a descriptive approach at the community or individual plant level. Nowadays these studies are evolving into physiological research on relationships between flooding stress and vegetation zonation. Current experiments aim to unravel the adaptive mechanisms whereby terrestrial plants cope with the peculiar conditions of the floodplain, from the whole plant down to the cell.
TL;DR: Modern comparative techniques may provide a new fusion between ecology, life histories, and reproductive behaviour in breeding systems, as shown in many birds, fishes, anurans, and insects.
Abstract: The study of breeding systems explores relationships between mating behaviour and parental care. Recent findings have shown that in many birds, fishes, anurans, and insects, females play a more active role than previously thought, by engaging in mate choice, mating with more than one male, and selecting genetic partners separately from social partners. Theoretical advances have improved our understanding of the effect of parental care on sex differences in mating behaviour, though less attention has been devoted to feedback in the opposite direction. The original emphasis on the role of ecology in determining breeding systems has been overshadowed by studies of individual interactions, but modern comparative techniques may provide a new fusion between ecology, life histories, and reproductive behaviour.
TL;DR: Analysis of data, results of models, and examination of basic 1 f -noise properties suggest that pink 1 < f noise, which lies midway between white noise and the random walk, might be the best null model of environment variation.
Abstract: Among ecologists, there has been a growing recognition of the importance of long-term correlations In environmental time series The family of 1 f -noises - fluctuations defined in terms of the different timescales present - is a useful approach to this problem White noise and the random walk, the two currently favoured descriptions of environmental fluctuations, lie at extreme ends of this family of processes Recent analyses of data, results of models, and examination of basic 1 f -noise properties, suggest that pink 1 f noise, which lies midway between white noise and the random walk, might be the best null model of environment variation If true, this would have important consequences for the interpretation of ecological time series and for ecological and evolutionary modelling
TL;DR: A growing number of studies suggests that species-range-size distributions are, in general, approximately lognormal, although interpretation is complicated by a variety of factors.
Abstract: Species-range-size distributions have received remarkably little attention in contrast to species-abundance distributions. However, recognition of the importance of regional scale phenomena for local assemblage structure, and the emergence of 'macroecology', have begun to change this situation. A growing number of studies suggests that these distributions are, in general, approximately lognormal, although interpretation is complicated by a variety of factors. Assuming the distribution pattern to be real, it can be viewed in terms of evolutionary and ecological determinants of species occurrences, although their relative significance remains unclear. The form of the distribution has a variety of important consequences, particularly for inventories of faunas and floras and for conservation.
TL;DR: Findings are important because past research on the role of dispersal in invertebrate dynamics has focused almost exclusively on how planktonic larval supply influences the establishment and maintenance of local assemblages, on the colonization of newly opened sites, or on the settlement success of new recruits.
Abstract: Recent work has shown that benthic invertebrate assemblages may be influenced in an ongoing fashion by dispersal. Water-column movements of meiofauna, juvenile insects and marine postlarvae are common and can act to alter greatly local dynamics such as predator-prey and competitive interactions in marine and stream ecosystems. These findings are important because past research on the role of dispersal in invertebrate dynamics has focused almost exclusively on how planktonic larval supply influences the establishment and maintenance of local assemblages, on the colonization of newly opened sites, or on the settlement success of new recruits. The emerging framework is that dispersal needs to be viewed as a regional process that may routinely influence local benthic dynamics, because fauna can move to and from water-column dispersal ‘pools' and may do so at frequent intervals.
TL;DR: Experimental approaches are starting to evolve to test the hypothesis that species diversity enhances productivity and stability in some ecosystems, but not in others, and the mechanisms underlying the functional role of species diversity.
Abstract: Attempts to unveil the relationships between the taxonomic diversity, productivity and stability of ecosystems continue to generate inconclusive, contradictory and controversial conclusions. New insights from recent studies support the hypothesis that species diversity enhances productivity and stability in some ecosystems, but not in others. Appreciation is growing for the ways that particular ecosystem features, such as environmental variability and nutrient stress, can influence biotic interactions. Alternatives to the diversity-stability hypothesis have been proposed, and experimental approaches are starting to evolve to test these hypotheses and to elucidate the mechanisms underlying the functional role of species diversity.
TL;DR: Although a variety of theories point out advantages to sex, most of them predict that a little sex and recombination can go a long way towards improving the fitness of a population, it remains unclear why obligate sex is so common.
Abstract: The evolution of sex has been the focus of considerable attention during recent years. There is some consensus that the solution to the mystery is that sex either enables the creation and spread of advantageous traits (possibly parasite resistance) or helps to purge the genome of deleterious mutations. Recent experimental work has allowed testing of some of the assumptions underlying the theoretical models, most particularly whether interactions between genes are synergistic and whether the mutation rate is adequately high. However, although a variety of theories point out advantages to sex, most of them predict that a little sex and recombination can go a long way towards improving the fitness of a population, and it remains unclear why obligate sex is so common.
TL;DR: Gene-culture coevolutionary theory is a branch of theoretical population genetics that models the transmission of genes and cultural traits from one generation to the next, exploring how they interact.
Abstract: Gene-culture coevolutionary theory is a branch of theoretical population genetics that models the transmission of genes and cultural traits from one generation to the next, exploring how they interact. These models have been employed to examine the adaptive advantages of learning and culture, to investigate the forces of cultural change, to partition the variance in complex human behavioral and personality traits, and to address specific cases in human evolution in which there is an interaction between genes and culture.
TL;DR: Accounting for social structure in population genetics leads to a different perspective on how genetic variation is partitoned and the rate at which genic diversity is lost in natural populations - a view that is more consistent with observed behaviors for the minimization of inbreeding.
Abstract: Populations are often composed of more than just randomly mating subpopulations - many organisms from social groups with distinct patterns of mating and dispersal. Such patterns have recieved much attention in behavioral ecology, yet theories of population genetics rarely take social structures into account. Consequently, population geneticists often report high levels of apparent in breeding and concomitantly low efective sizes, even for species that avoid mating between close kin. Recently, a view of gene dynamics has been introduced that takes dispersal and social structure into account. Accounting for social structure in population genetics leads to a different perspective on how genetic variation is partitoned and the rate at which genic diversity is lost in natural populations - a view that is more consistent with observed behaviors for the minimization of inbreeding.
TL;DR: Recent work on the relation between pollen dispersal and mating suggests that many features of floral design traditionally interpreted as anti-selling mechanisms may function to reduce the mating costs associated with large floral displays.
Abstract: Plants exhibit complex mating patterns because of their immobility, hermaphroditism and reliance on vectors for pollen transfer. Research on plant mating attempts to determine who mates with whom in plant populations and how and why mating patterns become evolutionarily modified. Most theoretical models of mating-system evolution have focused on the fitness consequences of selling and outcrossing, stimulating considerable empirical work on the ecology and genetics of inbreeding depression. Less attention has been given to how the mechanics of pollen dispersal influence the transmission of self and outcross gametes. Recent work on the relation between pollen dispersal and mating suggests that many features of floral design traditionally interpreted as anti-selling mechanisms may function to reduce the mating costs associated with large floral displays.