Showing papers in "Trends in Ecology and Evolution in 2001"
TL;DR: Crossfertilization between approaches based on species richness on the one hand, and on functional traits and types on the other, is a promising way of gaining mechanistic insight into the links between plant diversity and ecosystem processes and contributing to practical management for the conservation of diversity andcosystem services.
Abstract: The links between plant diversity and ecosystem functioning remain highly controversial. There is a growing consensus, however, that functional diversity, or the value and range of species traits, rather than species numbers per se, strongly determines ecosystem functioning. Despite its importance, and the fact that species diversity is often an inadequate surrogate, functional diversity has been studied in relatively few cases. Approaches based on species richness on the one hand, and on functional traits and types on the other, have been extremely productive in recent years, but attempts to connect their findings have been rare. Crossfertilization between these two approaches is a promising way of gaining mechanistic insight into the links between plant diversity and ecosystem processes and contributing to practical management for the conservation of diversity and ecosystem services.
2,756 citations
TL;DR: Although restricted to few taxa, these studies reveal clear relationships between the characteristics of releases and the species involved, and the successful establishment and spread of invaders.
Abstract: Predicting which species are probable invaders has been a long-standing goal of ecologists, but only recently have quantitative methods been used to achieve such a goal. Although restricted to few taxa, these studies reveal clear relationships between the characteristics of releases and the species involved, and the successful establishment and spread of invaders. For example, the probability of bird establishment increases with the number of individuals released and the number of release events. Also, the probability of plant invasiveness increases if the species has a history of invasion and reproduces vegetatively. These promising quantitative approaches should be more widely applied to allow us to predict patterns of invading species more successfully.
2,698 citations
TL;DR: The mechanisms that give rise to new species by divergent selection are reviewed, the alternatives are compared, recent tests in nature are summarized, and areas requiring research are highlighted.
Abstract: The ecological hypothesis of speciation is that reproductive isolation evolves ultimately as a consequence of divergent natural selection on traits between environments. Ecological speciation is general and might occur in allopatry or sympatry, involve many agents of natural selection, and result from a combination of adaptive processes. The main difficulty of the ecological hypothesis has been the scarcity of examples from nature, but several potential cases have recently emerged. I review the mechanisms that give rise to new species by divergent selection, compare ecological speciation with its alternatives, summarize recent tests in nature, and highlight areas requiring research.
1,820 citations
TL;DR: It is suggested that, although compensatory growth can bring quick benefits, it is also associated with a surprising variety of costs that are often not evident until much later in adult life.
Abstract: Nutritional conditions during key periods of development, when the architecture and modus operandi of the body become established, are of profound importance in determining the subsequent life-history trajectory of an organism. If developing individuals experience a period of nutritional deficit, they can subsequently show accelerated growth should conditions improve, apparently compensating for the initial setback. However, recent research suggests that, although compensatory growth can bring quick benefits, it is also associated with a surprising variety of costs that are often not evident until much later in adult life. Clearly, the nature of these costs, the timescale over which they are incurred and the mechanisms underlying them will play a crucial role in determining compensatory strategies. Nonetheless, such effects remain poorly understood and largely neglected by ecologists and evolutionary biologists.
1,784 citations
TL;DR: This work provides a categorization of hybridization to help guide management decisions and recognizes that nearly every situation involving hybridization is different enough that general rules are not likely to be effective.
Abstract: Rates of hybridization and introgression are increasing dramatically worldwide because of translocations of organisms and habitat modifications by humans. Hybridization has contributed to the extinction of many species through direct and indirect means. However, recent studies have found that natural hybridization has played an important role in the evolution of many plant and animal taxa. Determining whether hybridization is natural or anthropogenic is crucial for conservation, but is often difficult to achieve. Controversy has surrounded the setting of appropriate conservation policies to deal with hybridization and introgression. Any policy that deals with hybrids must be flexible and must recognize that nearly every situation involving hybridization is different enough that general rules are not likely to be effective. We provide a categorization of hybridization to help guide management decisions
1,649 citations
TL;DR: Whereas traditional phylogenetic methods assume bifurcating trees, several networking approaches have recently been developed to estimate intraspecific genealogies that take into account population-level phenomena.
Abstract: Intraspecific gene evolution cannot always be represented by a bifurcating tree. Rather, population genealogies are often multifurcated, descendant genes coexist with persistent ancestors and recombination events produce reticulate relationships. Whereas traditional phylogenetic methods assume bifurcating trees, several networking approaches have recently been developed to estimate intraspecific genealogies that take into account these population-level phenomena.
1,495 citations
TL;DR: Recent research shows a growing appreciation for the role of sprouting as a form of persistence in a diversity of ecosystems and tradeoffs between the two regeneration modes.
Abstract: Many woody plants can resprout and many ecosystems are dominated by resprouters. They persist in situ through disturbance events such as fire, flooding or wind storms. However, the importance of 'persistence' in plant demography has been neglected in favour of 'recruitment'. Thus much research on plant regeneration, conservation and evolution has focused on the importance of safe sites, seed and seedling banks, dispersal and germination with the implied importance of de novo replacement rather than persistence. Recent research shows a growing appreciation for the role of sprouting as a form of persistence in a diversity of ecosystems and tradeoffs between the two regeneration modes.
1,345 citations
TL;DR: This work reviews recent developments in methods and designs that aim to integrate sources of error to provide unbiased estimates of change in biological diversity and to suggest the potential causes.
Abstract: Monitoring programmes are being used increasingly to assess spatial and temporal trends of biological diversity, with an emphasis on evaluating the efficiency of management policies. Recent reviews of the existing programmes, with a focus on their design in particular, have highlighted the main weaknesses: the lack of well-articulated objectives and the neglect of different sources of error in the estimation of biological diversity. We review recent developments in methods and designs that aim to integrate sources of error to provide unbiased estimates of change in biological diversity and to suggest the potential causes.
1,242 citations
TL;DR: It is argued that rearrangements reduce gene flow more by suppressing recombination and extending the effects of linked isolation genes than by reducing fitness.
Abstract: Several authors have proposed that speciation frequently occurs when a population becomes fixed for one or more chromosomal rearrangements that reduce fitness when they are heterozygous This hypothesis has little theoretical support because mutations that cause a large reduction in fitness can be fixed through drift only in small, inbred populations Moreover, the effects of chromosomal rearrangements on fitness are unpredictable and vary significantly between plants and animals I argue that rearrangements reduce gene flow more by suppressing recombination and extending the effects of linked isolation genes than by reducing fitness This unorthodox perspective has significant implications for speciation models and for the outcomes of contact between neospecies and their progenitor(s)
1,237 citations
TL;DR: Natural abundances of the rare stable isotope of nitrogen, 15N, are now being used widely in research on N cycling in organisms and ecosystems as discussed by the authors, and recent progress towards overcoming some of the key technical problems and in revealing large-scale patterns in N cycle processes is discussed.
Abstract: Natural abundances of the rare stable isotope of nitrogen, 15N, are now being used widely in research on N cycling in organisms and ecosystems. 15N natural abundances are used in fundamentally different ways from traditional 15N tracers by integrating N cycle processes via N isotope fractionations and the mixing of various N-containing pools. This approach of using 15N natural abundances still requires certain technical and conceptual advances before it can be used routinely in ecological research. Here, the basis of the natural abundance 15N approach and opportunities for applying it in ecology are reviewed, and recent progress towards overcoming some of the key technical problems and in revealing large-scale patterns in N cycle processes is discussed.
1,151 citations
TL;DR: Host-pathogen models are essential for designing strategies for managing disease threats to humans, wild animals and domestic animals, and it is suggested that mass action has often been modelled wrongly.
Abstract: Host-pathogen models are essential for designing strategies for managing disease threats to humans, wild animals and domestic animals. The behaviour of these models is greatly affected by the way in which transmission between infected and susceptible hosts is modelled. Since host-pathogen models were first developed at the beginning of the 20th century, the 'mass action' assumption has almost always been used for transmission. Recently, however, it has been suggested that mass action has often been modelled wrongly. Alternative models of transmission are beginning to appear, as are empirical tests of transmission dynamics.
TL;DR: It is argued that more detailed studies are needed, examining extinction rates and other sources of variation in species richness, to convincingly conclude speciation by sexual selection.
Abstract: The power of sexual selection to drive changes in mate recognition traits gives it the potential to be a potent force in speciation. Much of the evidence to support this possibility comes from comparative studies that examine differences in the number of species between clades that apparently differ in the intensity of sexual selection. We argue that more detailed studies are needed, examining extinction rates and other sources of variation in species richness. Typically, investigations of extant natural populations have been too indirect to convincingly conclude speciation by sexual selection. Recent empirical work, however, is beginning to take a more direct approach and rule out confounding variables.
TL;DR: Assessment of food web and functional role frameworks can be used to identify ecological conditions that forecast the potential for unwanted secondary impacts and help safeguard against accidental, adverse effects on native ecosystems.
Abstract: Eradications of invasive species often have striking positive effects on native biota. However, recent research has shown that species removal in isolation can also result in unexpected changes to other ecosystem components. These secondary effects will become more likely as numbers of interacting invaders increase in ecosystems, and as exotics in late stages of invasion eliminate native species and replace their functional roles. Food web and functional role frameworks can be used to identify ecological conditions that forecast the potential for unwanted secondary impacts. Integration of eradication into a holistic process of assessment and restoration will help safeguard against accidental, adverse effects on native ecosystems.
TL;DR: Methods for avoiding Numts have now been tested, and several recent studies demonstrate the potential utility of Numt DNA sequences in evolutionary studies.
Abstract: Nuclear copies of mitochondrial DNA (mtDNA) have contaminated PCR-based mitochondrial studies of over 64 different animal species. Since the last review of these nuclear mitochondrial pseudogenes (Numts) in animals, Numts have been found in 53 of the species studied. The recent evidence suggests that Numts are not equally abundant in all species, for example they are more common in plants than in animals, and also more numerous in humans than in Drosophila. Methods for avoiding Numts have now been tested, and several recent studies demonstrate the potential utility of Numt DNA sequences in evolutionary studies. As relics of ancient mtDNA, these pseudogenes can be used to infer ancestral states or root mitochondrial phylogenies. Where they are numerous and selectively unconstrained, Numts are ideal for the study of spontaneous mutation in nuclear genomes.
TL;DR: The study of speciation has become one of the most active areas of evolutionary biology, and substantial progress has been made in documenting and understanding phenomena ranging from sympatric speciation and reinforcement to the evolutionary genetics of postzygotic isolation.
Abstract: The study of speciation has become one of the most active areas of evolutionary biology, and substantial progress has been made in documenting and understanding phenomena ranging from sympatric speciation and reinforcement to the evolutionary genetics of postzygotic isolation. This progress has been driven largely by empirical results, and most useful theoretical work has concentrated on making sense of empirical patterns. Given the complexity of speciation, mathematical theory is subordinate to verbal theory and generalizations about data. Nevertheless, mathematical theory can provide a useful classification of verbal theories; can help determine the biological plausibility of verbal theories; can determine whether alternative mechanisms of speciation are consistent with empirical patterns; and can occasionally provide predictions that go beyond empirical generalizations. We discuss recent examples of progress in each of these areas.
TL;DR: Increasing evidence suggests that the well-studied European southern and eastern refugia for thermophilous animal and plant taxa were supplemented by cryptic refugias in northern Europe during the Late Pleistocene, which could partially explain the ‘nonanalogue' mammalian assemblages of the Late pleistocene.
Abstract: Viewed from a geological perspective, present-day animal and plant communities in many parts of the world have a remarkably short history. The environmental revolution at the end of the Pleistocene, a mere 10 000 years ago, triggered major shifts in the ranges of species and hence composition of communities. Present-day communities in the boreal and temperate zones assembled at this time by combining species that survived the northern environment of the Last Cold Stage with those returning from more temperate refugia. Increasing evidence suggests that the well-studied European southern and eastern refugia for thermophilous animal and plant taxa were supplemented by cryptic refugia in northern Europe during the Late Pleistocene. These northern refugia would have been in areas of sheltered topography that provided suitable stable microclimates, and could partially explain the ‘nonanalogue' mammalian assemblages of the Late Pleistocene. They also have implications for phylogeography and speciation.
TL;DR: It might be time for a re-evaluation of the geographical classification of speciation modes in favor of one based primarily on evolutionary mechanisms.
Abstract: Sympatric speciation has become increasingly accepted in the past decade, as a result of new models substantiating its plausibility and new evidence that the conditions specified by the models are met in many natural populations. Retrospective phylogenetic and population genetic signatures of sympatric speciation have also been derived, and these are beginning to be tested. This new work has helped increase the acceptance of sympatric speciation as a plausible process, although it remains difficult to show conclusively that specific pairs of taxa have speciated through sympatric processes alone. It might be time for a re-evaluation of the geographical classification of speciation modes in favor of one based primarily on evolutionary mechanisms
TL;DR: The findings that elevated GCs can be a consequence of subordination or a cost of dominance complicate the conventional view of social stress, with broad ramifications for the evolution of dominance and reproductive suppression.
Abstract: In most cooperatively breeding birds and mammals, reproductive rates are lower for social subordinates than for dominants, and it is common for reproduction in subordinates to be completely suppressed. Early research conducted in captivity showed that losing fights can increase glucocorticoid (GC) secretion, a general response to stress. Because GCs can suppress reproduction, it has been widely argued that chronic stress might underlie reproductive suppression of social subordinates in cooperative breeders. Contradicting this hypothesis, recent studies of cooperative breeders in the wild show that dominant individuals have elevated GCs more often than do subordinates. The findings that elevated GCs can be a consequence of subordination or a cost of dominance complicate the conventional view of social stress, with broad ramifications for the evolution of dominance and reproductive suppression.
TL;DR: Recent research suggests that ectomycorrhizal fungi mobilize other essential plant nutrients directly from minerals through excretion of organic acids, which enables ectomy Corrhiza plants to utilize essential nutrients from insoluble mineral sources and affects nutrient cycling in forest systems.
Abstract: Plant nutrients, with the exception of nitrogen, are ultimately derived from weathering of primary minerals. Traditional theories about the role of ectomycorrhizal fungi in plant nutrition have emphasized quantitative effects on uptake and transport of dissolved nutrients. Qualitative effects of the symbiosis on the ability of plants to access organic nitrogen and phosphorus sources have also become increasingly apparent. Recent research suggests that ectomycorrhizal fungi mobilize other essential plant nutrients directly from minerals through excretion of organic acids. This enables ectomycorrhizal plants to utilize essential nutrients from insoluble mineral sources and affects nutrient cycling in forest systems.
TL;DR: This work discusses the use of chloroplast microsatellites in ecological and evolutionary studies of plants, as well as highlighting some of the potential problems associated with such use.
Abstract: The nonrecombinant, uniparentally inherited nature of organelle genomes makes them useful tools for evolutionary studies. However, in plants, detecting useful polymorphism at the population level is often difficult because of the low level of substitutions in the chloroplast genome, and because of the slow substitution rates and intramolecular recombination of mtDNA. Chloroplast microsatellites represent potentially useful markers to circumvent this problem and, to date, studies have demonstrated high levels of intraspecific variability. Here, we discuss the use of these markers in ecological and evolutionary studies of plants, as well as highlighting some of the potential problems associated with such use.
TL;DR: Combining both above- and belowground compartments in studies of multitrophic interactions throughout the life cycle of plants will improve the understanding of ecology and evolution in the real world.
Abstract: Plants function in a complex multitrophic environment. Most multitrophic studies, however, have almost exclusively focused on aboveground interactions, generally neglecting the fact that above- and belowground organisms interact. The spatial and temporal dynamics of above- and belowground herbivores, plant pathogens, and their antagonists, can differ in space and time. This affects the temporal interaction strengths and impacts of above- and belowground higher trophic level organisms on plants. Combining both above- and belowground compartments in studies of multitrophic interactions throughout the life cycle of plants will improve our understanding of ecology and evolution in the real world.
TL;DR: These microorganisms should provide novel, tractable systems for the analysis of social evolution and the application of evolutionary and ecological theory to understanding their behavior will aid in developing better means to control the many pathogenic bacteria that use social interactions to affect humans.
Abstract: Recent studies of microorganisms have revealed diverse complex social behaviors, including cooperation in foraging, building, reproducing, dispersing and communicating. These microorganisms should provide novel, tractable systems for the analysis of social evolution. The application of evolutionary and ecological theory to understanding their behavior will aid in developing better means to control the many pathogenic bacteria that use social interactions to affect humans.
TL;DR: The relationship between species is usually represented as a bifurcating tree with the branching points representing speciation events, but a different picture is emerging from new empirical evidence, particularly that based on multiple loci or on surveys with a wide geographical scope.
Abstract: The relationship between species is usually represented as a bifurcating tree with the branching points representing speciation events. The ancestry of genes taken from these species can also be represented as a tree, with the branching points representing ancestral genes. The time back to the branching points, and even the branching order, can be different between the two trees. This possibility is widely recognized, but the discrepancies are often thought to be small. A different picture is emerging from new empirical evidence, particularly that based on multiple loci or on surveys with a wide geographical scope. The discrepancies must be taken into account when estimating the timing of speciation events, especially the more recent branches. On the positive side, the different timings at different loci provide information about the ancestral populations.
TL;DR: The links between canalization, plasticity and developmental stability, the three major processes involved in the control of phenotypic variability, are clarified.
Abstract: The relationship between genotype and phenotype is not one to one. This statement is central to our understanding of how natural selection shapes phenotypic evolution. Here, we clarify the links between canalization, plasticity and developmental stability, the three major processes involved in the control of phenotypic variability. We present a short historical review, including the original definitions of these concepts, and then summarize their current meaning and use, highlighting possible sources of confusion. Some of the perspectives allowed by a more synthetic conceptual framework are presented, in the light of the recent advances in molecular and developmental genetics.
TL;DR: Results show that data quality, as well as the choice of surrogates for biodiversity, could be critical for successful reserve design, and the impact of computational site-selection tools in applied conservation planning has been minimal.
Abstract: Sophisticated computational methods have been developed to help us to identify sets of nature reserves that maximize the representation of regional diversity, but, until recently, the methods have not dealt explicitly and directly with the main goal of reserve networks, that of the long-term maintenance of biodiversity. Furthermore, the successful application of current methods requires reliable information about species distributions, which is not always available. Recent results show that data quality, as well as the choice of surrogates for biodiversity, could be critical for successful reserve design. Because of these problems and a lack of communication between scientists and managers, the impact of computational site-selection tools in applied conservation planning has been minimal.
TL;DR: The authors' increasing ability to predict El Niño effects can be used to enhance management strategies for the restoration of degraded ecosystems, and suggest that the predicted change in extreme climatic events resulting from global warming could profoundly alter biodiversity and ecosystem functioning in many regions of the world.
Abstract: New studies are showing that the El Nino Southern Oscillation (ENSO) has major implications for the functioning of different ecosystems, ranging from deserts to tropical rain forests. ENSO-induced pulses of enhanced plant productivity can cascade upward through the food web invoking unforeseen feedbacks, and can cause open dryland ecosystems to shift to permanent woodlands. These insights suggest that the predicted change in extreme climatic events resulting from global warming could profoundly alter biodiversity and ecosystem functioning in many regions of the world. Our increasing ability to predict El Nino effects can be used to enhance management strategies for the restoration of degraded ecosystems.
TL;DR: It is not only phytoplankton biomass, taxonomy or activity, but also food-web structure and dynamics that drive the oceanic production of atmospheric sulfur, and the viewpoint on the ecological and evolutionary basis of this amazing marine biota-atmosphere link is changing.
Abstract: Biological production of the volatile compound dimethylsulfide in the ocean is the main natural source of tropospheric sulfur on a global scale, with important consequences for the radiative balance of the Earth. In the late 1980s, a Gaian feedback link between marine phytoplankton and climate through the release of atmospheric sulfur was hypothesized. However, the idea of microalgae producing a substance that could regulate climate has been criticized on the basis of its evolutionary feasibility. Recent advances have shown that volatile sulfur is a result of ecological interactions and transformation processes through planktonic food webs. It is, therefore, not only phytoplankton biomass, taxonomy or activity, but also food-web structure and dynamics that drive the oceanic production of atmospheric sulfur. Accordingly, the viewpoint on the ecological and evolutionary basis of this amazing marine biota-atmosphere link is changing.
TL;DR: This work has shown that neutral variants might be used to identify adaptive variants, but the overlay of different mutational processes and selective regimes suggests that extreme caution should be used in making such identifications.
Abstract: Genetic studies in endangered species have become widespread in the past decade, and with new information from various genome projects, new applications and insights are forthcoming. Generally, neutral variants are used for conservation applications, and when combined with highly variable loci and/or many more markers, these approaches should become much more informative. Conservation genetics is also concerned with detrimental and adaptive variation, which are more difficult to identify and characterize; however, the ability to predict the extent of such variation might become more successful and applied in future conservation efforts. Neutral variants might be used to identify adaptive variants, but the overlay of different mutational processes and selective regimes suggests that extreme caution should be used in making such identifications.
TL;DR: This work discusses recent practical and theoretical advances in phylogenies derived from molecular data and outlines how future work should benefit from incorporating data from genealogical and phylogeographical scales.
Abstract: Species-level phylogenies derived from molecular data provide an indirect record of the speciation events that have led to extant species. This offers enormous potential for investigating the general causes and rates of speciation within clades. To make the most of this potential, we should ideally sample all the species in a higher group, such as a genus, ensure that those species reflect evolutionary entities within the group, and rule out the effects of other processes, such as extinction, as explanations for observed patterns. We discuss recent practical and theoretical advances in this area and outline how future work should benefit from incorporating data from genealogical and phylogeographical scales.
TL;DR: In this paper, the authors present arguments that PVAs can only be accurate at predicting extinction probabilities if data are extensive and reliable, and if the distribution of vital rates between individuals and years can be assumed stationary in the future, or if any changes can be accurately predicted.
Abstract: A recent study by Brook et al. empirically tested the performance of population viability analysis (PVA) using data from 21 populations across a wide range of species. The study concluded that PVAs are good at predicting the future dynamics of populations. We suggest that this conclusion is a result of a bias in the studies that Brook et al. included in their analyses. We present arguments that PVAs can only be accurate at predicting extinction probabilities if data are extensive and reliable, and if the distribution of vital rates between individuals and years can be assumed stationary in the future, or if any changes can be accurately predicted. In particular, we note that although catastrophes are likely to have precipitated many extinctions, estimates of the probability of catastrophes are unreliable.