Showing papers in "Annual Review of Ecology, Evolution, and Systematics in 2004"
TL;DR: Active adaptive management and governance of resilience will be required to sustain desired ecosystem states and transform degraded ecosystems.
Abstract: ▪ Abstract We review the evidence of regime shifts in terrestrial and aquatic environments in relation to resilience of complex adaptive ecosystems and the functional roles of biological diversity in this context. The evidence reveals that the likelihood of regime shifts may increase when humans reduce resilience by such actions as removing response diversity, removing whole functional groups of species, or removing whole trophic levels; impacting on ecosystems via emissions of waste and pollutants and climate change; and altering the magnitude, frequency, and duration of disturbance regimes. The combined and often synergistic effects of those pressures can make ecosystems more vulnerable to changes that previously could be absorbed. As a consequence, ecosystems may suddenly shift from desired to less desired states in their capacity to generate ecosystem services. Active adaptive management and governance of resilience will be required to sustain desired ecosystem states and transform degraded ecosystems...
3,297 citations
TL;DR: In this paper, the authors examined responses to land use under different management strategies and that employs response variables that have greater diagnostic value than many of the aggregated measures in current use.
Abstract: ▪ Abstract Local habitat and biological diversity of streams and rivers are strongly influenced by landform and land use within the surrounding valley at multiple scales. However, empirical associations between land use and stream response only varyingly succeed in implicating pathways of influence. This is the case for a number of reasons, including (a) covariation of anthropogenic and natural gradients in the landscape; (b) the existence of multiple, scale-dependent mechanisms; (c) nonlinear responses; and (d) the difficulties of separating present-day from historical influences. Further research is needed that examines responses to land use under different management strategies and that employs response variables that have greater diagnostic value than many of the aggregated measures in current use. In every respect, the valley rules the stream. H.B.N. Hynes (1975)
3,151 citations
TL;DR: It is shown that pollination syndromes provide great utility in understanding the mechanisms of floral diversification and the importance of organizing pollinators into functional groups according to presumed similarities in the selection pressures they exert.
Abstract: ▪ Abstract Floral evolution has often been associated with differences in pollination syndromes. Recently, this conceptual structure has been criticized on the grounds that flowers attract a broader spectrum of visitors than one might expect based on their syndromes and that flowers often diverge without excluding one type of pollinator in favor of another. Despite these criticisms, we show that pollination syndromes provide great utility in understanding the mechanisms of floral diversification. Our conclusions are based on the importance of organizing pollinators into functional groups according to presumed similarities in the selection pressures they exert. Furthermore, functional groups vary widely in their effectiveness as pollinators for particular plant species. Thus, although a plant may be visited by several functional groups, the relative selective pressures they exert will likely be very different. We discuss various methods of documenting selection on floral traits. Our review of the literatur...
1,813 citations
TL;DR: Given the influence of deer on other organisms and natural processes, ecologists should actively participate in efforts to understand, monitor, and reduce the impact of deer in natural ecosystems.
Abstract: ▪ Abstract Deer have expanded their range and increased dramatically in abundance worldwide in recent decades. They inflict major economic losses in forestry, agriculture, and transportation and contribute to the transmission of several animal and human diseases. Their impact on natural ecosystems is also dramatic but less quantified. By foraging selectively, deer affect the growth and survival of many herb, shrub, and tree species, modifying patterns of relative abundance and vegetation dynamics. Cascading effects on other species extend to insects, birds, and other mammals. In forests, sustained overbrowsing reduces plant cover and diversity, alters nutrient and carbon cycling, and redirects succession to shift future overstory composition. Many of these simplified alternative states appear to be stable and difficult to reverse. Given the influence of deer on other organisms and natural processes, ecologists should actively participate in efforts to understand, monitor, and reduce the impact of deer on ...
1,779 citations
TL;DR: In this paper, the authors identify four fundamental mechanisms that cause edge responses: ecological flows, access to spatially separated resources, resource mapping, and species interactions, and present a conceptual framework that identifies the pathways through which these four mechanisms can influence distributions, ultimately leading to new ecological communities near habitat edges.
Abstract: ▪ Abstract Edge effects have been studied for decades because they are a key component to understanding how landscape structure influences habitat quality. However, making sense of the diverse patterns and extensive variability reported in the literature has been difficult because there has been no unifying conceptual framework to guide research. In this review, we identify four fundamental mechanisms that cause edge responses: ecological flows, access to spatially separated resources, resource mapping, and species interactions. We present a conceptual framework that identifies the pathways through which these four mechanisms can influence distributions, ultimately leading to new ecological communities near habitat edges. Next, we examine a predictive model of edge responses and show how it can explain much of the variation reported in the literature. Using this model, we show that, when observed, edge responses are largely predictable and consistent. When edge responses are variable for the same species ...
1,244 citations
TL;DR: In addition to intraspecific synchrony, there are many examples of synchrony among populations of different species, the causes of which are similarly complex and difficult to identify.
Abstract: ▪ Abstract Spatial synchrony refers to coincident changes in the abundance or other time-varying characteristics of geographically disjunct populations. This phenomenon has been documented in the dynamics of species representing a variety of taxa and ecological roles. Synchrony may arise from three primary mechanisms:(a) dispersal among populations, reducing the size of relatively large populations and increasing relatively small ones; (b) congruent dependence of population dynamics on a synchronous exogenous random factor such as temperature or rainfall, a phenomenon known as the “Moran effect”; and (c) trophic interactions with populations of other species that are themselves spatially synchronous or mobile. Identification of the causes of synchrony is often difficult. In addition to intraspecific synchrony, there are many examples of synchrony among populations of different species, the causes of which are similarly complex and difficult to identify. Furthermore, some populations may exhibit complex sp...
779 citations
TL;DR: The use of ecological indicators has been widely accepted by scientists, environmental managers, and the general public as mentioned in this paper, and they have been used to assess the condition of the environment, as early warning signals of ecological problems, and as barometers for trends in ecological resources.
Abstract: ▪ Abstract Ecological indicators have widespread appeal to scientists, environmental managers, and the general public. Indicators have long been used to detect changes in nature, but the scientific maturation in indicator development primarily has occurred in the past 40 years. Currently, indicators are mainly used to assess the condition of the environment, as early-warning signals of ecological problems, and as barometers for trends in ecological resources. Use of ecological indicators requires clearly stated objectives; the recognition of spatial and tempor al scales; assessments of statistical variability, precision, and accuracy; linkages with specific stressors; and coupling with economic and social indicators. Legislatively mandated use of ecological indicators occurs in many countries worldwide and is included in international accords. As scientific advancements and innovation in the development and use of ecological indicators continue through applications of molecular biology, computer technolog...
772 citations
TL;DR: Molecular phylogenies suggest multiple dispersal events into, out of, and within the SWAFR throughout the Cretaceous and Cenozoic; in many phylogenetically unrelated clades; and from many directions.
Abstract: ▪ Abstract Like South Africa's Greater Cape Floristic Region, the Southwest Australian Floristic Region (SWAFR) is species rich, with a Mediterranean climate and old, weathered, nutrient-deficient landscapes. This region has 7380 native vascular plants (species/subspecies): one third described since 1970, 49% endemic, and 2500 of conservation concern. Origins are complex. Molecular phylogenies suggest multiple dispersal events into, out of, and within the SWAFR throughout the Cretaceous and Cenozoic; in many phylogenetically unrelated clades; and from many directions. Either explosive speciation or steady cladogenesis occurred among some woody sclerophyll and herbaceous families from the mid-Tertiary in response to progressive aridity. Genomic coalescence was sometimes involved. Rainforest taxa went extinct by the Pleistocene. Old lineages nevertheless persist as one endemic order (Dasypogonales) and 6–11 endemic families. Such a rich flora on old landscapes that have been exposed to European land-use pra...
771 citations
TL;DR: It is concluded that all methods will sometimes fail to delimit species boundaries properly or will give conflicting results, and that virtually all methods require researchers to make qualitative judgments.
Abstract: ▪ Abstract Species are routinely used as fundamental units of analysis in biogeography, ecology, macroevolution, and conservation biology. A large literature focuses on defining species conceptually, but until recently little attention has been given to the issue of empirically delimiting species. Researchers confronted with the task of delimiting species in nature are often unsure which method(s) is (are) most appropriate for their system and data type collected. Here, we review twelve of these methods organized into two general categories of tree- and nontree-based approaches. We also summarize the relevant biological properties of species amenable to empirical evaluation, the classes of data required, and some of the strengths and limitations of each method. We conclude that all methods will sometimes fail to delimit species boundaries properly or will give conflicting results, and that virtually all methods require researchers to make qualitative judgments. These facts, coupled with the fuzzy nature o...
720 citations
TL;DR: Here, the evidence for criteria identified to detect community-based, diffuse coevolution is reviewed and the evidence that multispecies interactions have demographic consequences for populations, as well as evolutionary consequences is reviewed.
Abstract: ▪ Abstract Ecologists and evolutionary biologists are broadly interested in how the interactions among organisms influence their abundance, distribution, phenotypes, and genotypic composition. Recently, we have seen a growing appreciation of how multispecies interactions can act synergistically or antagonistically to alter the ecological and evolutionary outcomes of interactions in ways that differ fundamentally from outcomes predicted by pairwise interactions. Here, we review the evidence for criteria identified to detect community-based, diffuse coevolution. These criteria include (a) the presence of genetic correlations between traits involved in multiple interactions, (b) interactions with one species that alter the likelihood or intensity of interactions with other species, and (c) nonadditive combined effects of multiple interactors. In addition, we review the evidence that multispecies interactions have demographic consequences for populations, as well as evolutionary consequences. Finally, we expl...
506 citations
TL;DR: Predator-induced plasticity in metamorphic traits may be related to predator-induced changes in larval morphology and behavior, and future work should incorporate more detailed studies of growth rate, morphology, and behavior during the larval period.
Abstract: ▪ Abstract Predator-induced phenotypic plasticity is widespread in nature and includes variation in life history, morphology, and behavior. In organisms with complex life histories, predator-induced phenotypic plasticity in the larval period has been widely documented. Several models predict how organisms should alter their size at and time to metamorphosis in response to an increased risk of predation. A survey of empirical studies finds that these theoretical predictions are frequently met. However, no one model performs the best. Additionally, there are several results not predicted by any model. Predator-induced plasticity in metamorphic traits may be related to predator-induced changes in larval morphology and behavior. Predictions of predator effects on larval traits are generally met, except for direct costs of predator-induced morphological phenotypes. Future work should incorporate more detailed studies of growth rate, morphology, and behavior during the larval period, as well as studies of size-...
TL;DR: The evidence supporting the current understanding of metazoan phylogeny is discussed on a clade by clade basis, supported by molecular and morphological data.
Abstract: ▪ Abstract Molecular tools have profoundly rearranged our understanding of metazoan phylogeny. Initially based on the nuclear small ribosomal subunit (SSU or 18S) gene, recent hypotheses have been corroborated by several sources of data (including the nuclear large ribosomal subunit, Hox genes, mitochondrial gene order, concatenated mitochondrial genes, and the myosin II heavy chain gene). Herein, the evidence supporting our current understanding is discussed on a clade by clade basis. Bilaterian animals consist of three clades: Deuterostomia, Lophotrochozoa, and Ecdysozoa. Each clade is supported by molecular and morphological data. Deuterostomia is smaller than traditionally recognized, consisting of hemichordates, echinoderms, chordates, and Xenoturbella (an enigmatic worm-like animal). Lophotrochozoa groups animals with a lophophore feeding apparatus (Brachiopoda, Bryozoa, and Phoronida) and trochophore larvae (e.g., annelids and mollusk), as well as several other recognized phyla (e.g., platyhelmin t...
TL;DR: Salamanders are cryptic and, though largely unrecognized as such, extremely abundant vertebrates in a variety of primarily forest and grassland environments, where they regulate food webs and contribute to ecosystem resilience-resistance (= stability).
Abstract: ▪ Abstract Salamanders are cryptic and, though largely unrecognized as such, extremely abundant vertebrates in a variety of primarily forest and grassland environments, where they regulate food webs and contribute to ecosystem resilience-resistance (= stability) in several ways: (a) As mid-level vertebrate predators, they provide direct and indirect biotic control of species diversity and ecosystem processes along grazer and detritus pathways; (b) via their migrations, they connect energy and matter between aquatic and terrestrial landscapes; (c) through association with underground burrow systems, they contribute to soil dynamics; and (d) they supply high-quality and slowly available stores of energy and nutrients for tertiary consumers throughout ecological succession. Salamanders also can provide an important service to humans through their use as cost-effective and readily quantifiable metrics of ecosystem health and integrity. The diverse ecological roles of salamanders in natural areas underscore th...
TL;DR: The literature on the ecology of woodland herbs is reviewed because a number of species have become rare or threatened owing to the conversion of forests to other land uses, competition by alien plant species, and increased abundance of native wildlife that negatively impact woodland herbs.
Abstract: ▪ Abstract The diversity of woodland herbs is one of the most striking features of deciduous forests in the temperate zone. Here I review the literature on the ecology of woodland herbs. The review is timely because, since Paulette Bierzychudek's seminal review of the subject in 1982, a number of species have become rare or threatened owing to the conversion of forests to other land uses, competition by alien plant species, and increased abundance of native wildlife that negatively impact woodland herbs (e.g., white-tailed deer). Although the basic biology of woodland herbs is mostly known, few species have been studied in detail, and we are only able to make broad generalities about their ecology. We are especially lacking in information needed to conserve and restore species in altered and threatened habitats.
TL;DR: Indirect evidence exists that warming increased disease in turtles, and protection, pollution, and terrestrial pathogens increased mammal disease, and release from overfished predators increased sea urchin disease.
Abstract: ▪ Abstract Many factors (climate warming, pollution, harvesting, introduced species) can contribute to disease outbreaks in marine life Concomitant increases in each of these makes it difficult to attribute recent changes in disease occurrence or severity to any one factor For example, the increase in disease of Caribbean coral is postulated to be a result of climate change and introduction of terrestrial pathogens Indirect evidence exists that (a) warming increased disease in turtles; (b) protection, pollution, and terrestrial pathogens increased mammal disease; (c) aquaculture increased disease in mollusks; and (d) release from overfished predators increased sea urchin disease In contrast, fishing and pollution may have reduced disease in fishes In other taxa (eg, sea grasses, crustaceans, sharks), there is little evidence that disease has changed over time The diversity of patterns suggests there are many ways that environmental change can interact with disease in the ocean
TL;DR: Factors influencing the ecological and evolutionary dynamics of novel plant-pathogen interactions are explored, using that evolutionary ecology framework to provide insight into three important practical applications: emerging diseases, biological invasions, and biological control.
Abstract: ▪ Abstract Novel plant-pathogen combinations occur whenever pathogen or plant species are introduced to regions outside their native range. Whether a pathogen is able to acquire a new host depends on the genetic compatibility between the two, through either preadaptation of the pathogen or subsequent evolutionary change. The ecological outcome of the novel interaction—for example, a spreading disease epidemic or the extinction of an incipient plant invasion—depends on the life history of the pathogen, opportunities for rapid evolution of virulence or resistance, and the presence of a suitable environment. We review recent work on the biology of pathogen virulence and host resistance, their mechanisms, and their costs. We then explore factors influencing the ecological and evolutionary dynamics of novel plant-pathogen interactions, using that evolutionary ecology framework to provide insight into three important practical applications: emerging diseases, biological invasions, and biological control.
TL;DR: A review of five key evolutionary issues pertaining to animal cognition, defined as the neuronal processes concerned with the acquisition, retention, and use of information, finds ample evidence for genetically based individual variation in cognitive traits.
Abstract: ▪ Abstract This review focuses on five key evolutionary issues pertaining to animal cognition, defined as the neuronal processes concerned with the acquisition, retention, and use of information. Whereas the use of information, or decision making, has been relatively well examined by students of behavior, evolutionary aspects of other cognitive traits that affect behavior, including perception, learning, memory, and attention, are less well understood. First, there is ample evidence for genetically based individual variation in cognitive traits, although much of the information for some traits comes from humans. Second, several studies documented positive association between cognitive abilities and performance measures linked to fitness. Third, information on the evolution of cognitive traits is available primarily for color vision and decision making. Fourth, much of the data on plasticity of cognitive traits appears to reflect nonadaptive phenotypic plasticity, perhaps because few evolutionary analyses ...
TL;DR: It is argued that properties of vocal mechanisms (control, production, and ontogeny) constrain vocal potential and may thus limit pathways of meme evolution and how vocal mechanisms may constrain song evolution under five scenarios of drift and selection.
Abstract: ▪ Abstract Bird song provides an unusually impressive illustration of vertebrate behavioral diversification. Research on bird song evolution traditionally focuses on factors that enhance song diversity, such as cultural transmission and sexual selection. Recent advances in the study of proximate mechanisms of vocal behavior, however, provide opportunities for studying mechanistic constraints on song evolution. The main goal of this review is to examine, from both conceptual and empirical perspectives, how proximate mechanisms might temper patterns of song evolution. We provide an overview of the two “substrates” of song evolution, memes and vocal mechanisms. We argue that properties of vocal mechanisms (control, production, and ontogeny) constrain vocal potential and may thus limit pathways of meme evolution. We then consider how vocal mechanisms may constrain song evolution under five scenarios of drift and selection and examine four specific song traits for which mechanistic constraints appear to counte...
TL;DR: The lack of year-round availability of fruits may make survival in deforested or fragmented areas difficult for frugivores, and extension of large predators, superior competitors, pollinators, and seed dispersers may have repercussions for tropical ecosystem functioning.
Abstract: ▪ Abstract Tropical forests are being lost at an alarming rate. Studies from various tropical locations report losses of forest birds as possibly direct or indirect results of deforestation. Although it may take a century for all the sensitive species to be extirpated from a site following habitat loss, species with larger or heavier bodies and those foraging on insects, fruits, or both are particularly extinction prone. Larger- or heavier-bodied species may occur at low densities, increasing their vulnerability to habitat alterations. Insectivores are vulnerable for reasons such as the loss of preferred microhabitats, poor dispersal abilities, and/or ground nesting habits that make them susceptible to predation. The lack of year-round availability of fruits may make survival in deforested or fragmented areas difficult for frugivores. Extirpation of large predators, superior competitors, pollinators, and seed dispersers may have repercussions for tropical ecosystem functioning. Large tropical reserves tha...
TL;DR: The evolutionary succession of marine photoautotrophs began with the origin of photosynthesis in the Archean Eon, and three groups of chlorophyll c–containing eukaryotes, the dinoflagellates, coccolithophorids, and diatoms began evolutionary trajectories that have culminated in ecological dominance in the con...
Abstract: ▪ Abstract The evolutionary succession of marine photoautotrophs began with the origin of photosynthesis in the Archean Eon, perhaps as early as 3.8 billion years ago. Since that time, Earth's atmosphere, continents, and oceans have undergone substantial cyclic and secular physical, chemical, and biological changes that selected for different phytoplankton taxa. Early in the history of eukaryotic algae, between 1.6 and 1.2 billion years ago, an evolutionary schism gave rise to “green” (chlorophyll b–containing) and “red” (chlorophyll c–containing) plastid groups. Members of the “green” plastid line were important constituents of Neoproterozoic and Paleozoic oceans, and, ultimately, one green clade colonized land. By the mid-Mesozoic, the green line had become ecologically less important in the oceans. In its place, three groups of chlorophyll c–containing eukaryotes, the dinoflagellates, coccolithophorids, and diatoms, began evolutionary trajectories that have culminated in ecological dominance in the con...
TL;DR: Vertebrate dispersal of fruits and seeds is a common feature of many modern angiosperms and gymnosperms, yet the evolution and frequency of this feature in the fossil record remain unclear.
Abstract: ▪ Abstract Vertebrate dispersal of fruits and seeds is a common feature of many modern angiosperms and gymnosperms, yet the evolution and frequency of this feature in the fossil record remain unclear. Increasingly complex information suggests that (a) plants had the necessary morphological features for vertebrate dispersal by the Pennsylvanian, but possibly in the absence of clear vertebrate dispersal agents; (b) vertebrate herbivores first diversified in the Permian, and consistent dispersal relationships became possible; (c) the Mesozoic was dominated by large herbivorous dinosaurs, possible sources of diffuse, whole-plant dispersal; (d) simultaneously, several groups of small vertebrates, including lizards and, in the later Mesozoic, birds and mammals, could have established more specific vertebrate-plant associations, but supporting evidence is rudimentary; and (e) the diversification of small mammals and birds in the Tertiary established a consistent basis for organ-level interactions, allowing for t...
TL;DR: In aquatic ecosystems, mutualisms can transform consumers, competitors, and parasites into mutualists, even while they consume, compete with, or parasitize their partner species as mentioned in this paper.
Abstract: ▪ Abstract Mutualisms occur when interactions between species produce reciprocal benefits. However, the outcome of these interactions frequently shifts from positive, to neutral, to negative, depending on the environmental and community context, and indirect effects commonly produce unexpected mutualisms that have community-wide consequences. The dynamic, and context dependent, nature of mutualisms can transform consumers, competitors, and parasites into mutualists, even while they consume, compete with, or parasitize their partner species. These dynamic, and often diffuse, mutualisms strongly affect community organization and ecosystem processes, but the historic focus on pairwise interactions decoupled from their more complex community context has obscured their importance. In aquatic systems, mutualisms commonly support ecosystem-defining foundation species, underlie energy and nutrient dynamics within and between ecosystems, and provide mechanisms by which species can rapidly adjust to ecological vari...
TL;DR: There is great potential for enhanced interaction between paleoecology and neoecology in understanding spatiotemporal complexity of ecological dynamics and greater uniformity is needed in the approaches to studying the problem.
Abstract: Studies of plant and animal assemblages from both the terrestrial and the marine fossil records reveal persistence for extensive periods of geological time, sometimes millions of years. Persistence does not require lack of change or the absence of variation from one occurrence of the assemblage to the next in geological time. It does, however, imply that assemblage composition is bounded and that variation occurs within those bounds. The principal cause for these patterns appears to be species-, and perhaps clade-level, environmental fidelity that results in long-term tracking of physical conditions. Other factors that influence persistent recurrence of assemblages are historical, biogeographic effects, the law of large numbers, niche differentiation, and biotic interactions. Much research needs to be done in this area, and greater uniformity is needed in the approaches to studying the problem. However, great potential also exists for enhanced interaction between paleoecology and neoecology in understanding spatiotemporal complexity of ecological dynamics.
TL;DR: The escape of transgenes into wild populations, via hybridization and introgression, could lead to increased weediness or to the invasion of new habitats by the wild population.
Abstract: ▪ Abstract Ecological risks associated with the release of transgenic crops include nontarget effects of the crop and the escape of transgenes into wild populations. Nontarget effects can be of two sorts: (a) unintended negative effects on species that do not reduce yield and (b) greater persistence of the crop in feral populations. Conventional agricultural methods, such as herbicide and pesticide application, have large and well-documented nontarget effects. To the extent that transgenes have more specific target effects, transgenic crops may have fewer nontarget effects. The escape of transgenes into wild populations, via hybridization and introgression, could lead to increased weediness or to the invasion of new habitats by the wild population. In addition, native species with which the wild plant interacts (including herbivores, pathogens, and other plant species in the community) could be negatively affected by “transgenic-wild” plants. Conventional crop alleles have facilitated the evolution of inc...