Search

Intraspecific variation in host susceptibility to individual parasite species is common, yet how these effects scale to mediate the structure of diverse parasite communities in nature is less well understood. To address this knowledge gap, we tested how host genetic identity affects parasite communities on restored reefs seeded with juvenile oysters from different sources—a regional commercial hatchery or one of two wild progenitor lines. We assessed prevalence and intensity of three micro- and two macroparasite species for 4 years following restoration. Despite the spatial proximity of restored reefs, oyster source identity strongly predicted parasite community prevalence across all years, with sources varying in their relative susceptibility to different parasites. Oyster seed source also predicted reef-level parasite intensities across space and through time. Our results highlight that host intraspecific variation can shape parasite community structure in natural systems, and reinforce the importance of considering source identity and diversity in restoration design.

Microgeographic genetic divergence can create fine-scale trait variation. When such divergence occurs within foundation species, then it might impact community structure and ecosystem function and cause other cascading ecological effects. We tested for parallel microgeographic trait and genetic divergence in

Nearshore foundation species in coastal and estuarine systems (e.g., salt marsh grasses, mangroves, seagrasses, corals) drive the ecological functions of ecosystems and entire biomes by cre...

Climate-driven range shifts can result in altered mixtures of foundation species that can affect ecosystem structure and function. Higher diversity mixed assemblages may moderate disturbance impacts, yet this prediction has rarely been tested. The Deepwater Horizon oil spill provided an opportunity to examine the effects of salt marsh foundation species identity and composition on the response of both plant and faunal communities to oil disturbance. In the northern Gulf of Mexico, salt marshes are typically dominated by the foundation species smooth cordgrass, Spartina alterniflora. However, the sub-tropical black mangrove, Avicennia germinans, is expanding northward and increasingly growing with, and even replacing, Spartina. Based on a series of field surveys in the Chandeleur Islands, Louisiana, we found that oil exposure had few impacts on the plant community 5 yr post-oiling, though oil disturbance shifted the interaction among foundation species, increasing Avicennia’s competitive advantage and likely enhancing mangrove expansion. In contrast, abundance of the epibenthic animal community was reduced by ~30% and community composition was altered at oiled sites. Mixed foundation species assemblages provided few reductions in oil impacts within either trophic level. Strong habitat associations of epibenthic taxa, coupled with oil effects on individual foundation species, likely suppressed any advantage of mixed vegetation on the associated fauna. Our survey highlights that plant and epibenthic animal responses to disturbance can be decoupled, emphasizing the importance of examining both simultaneously to better understand and predict long-term responses.

Sexual reproduction is the primary source of genotypic diversity in seagrass meadows, with important implications for both the evolutionary potential and ecological function of these habitats. However, relatively little is known about seagrass pollination dynamics or how genetic diversity in life history stage may influence genetic diversity in another. We used microsatellite DNA markers to assess how genetic diversity of adult shoots and seeds covaried across the depth gradient in two Zostera marina L. (eelgrass) meadows in Massachusetts (USA). Despite strong spatial patterns in the density of reproductive shoots and genetic evidence for limited pollen dispersal, we found modest corresponding variation in outcrossing rates and paternal diversity. Across spatial scales from quadrats to sites, there was a positive association between the density of flowering shoots and clonal richness; however, other measures of diversity (e.g., allelic richness and heterozygosity) showed weak or opposing patterns with reproductive effort, and neither flowering effort nor local genotypic richness of adults were good proxies for seed diversity. Self-pollinated seeds were significantly smaller than their outcrossed half-siblings, and our data suggest that selection against selfed seeds varies spatially within and among meadows, possibly due to high competition with vegetative shoots in the dense shallow margin. Understanding the processes that shape genetic diversity in seagrass populations is key to their conservation and management; our study highlights the challenges of inferring the contribution of sexual reproduction to population structure using a single metric or life history stage.

Variation in the timing of sexual reproduction, as well as differences in the relative investment in asexual vs sexual reproduction, commonly occurs among populations. Less is known about such variation within populations, yet small-scale differences in phenology and reproductive investment have the potential to limit gene flow and consequently the adaptive capacity of populations. We examined within-site variation in sexual reproduction in seagrasses, marine angiosperms that can reproduce asexually via clonal propagation or sexually via flowering, and that form the foundation of critical marine ecosystems globally. Many factors, including light availability, temperature, nutrient availability, and genetic identity, influence the rate and timing of seagrass flower development, yet little is known about how phenology varies across common environmental gradients within individual seagrass meadows. Here, we investigate how the density, morphology, and phenology of eelgrass (Zostera marina) differs across depths within multiple sites in New England. Despite variation in the proportion of reproductive vs vegetative shoots across sites, reproductive investment did not differ across depths within sites. However, a comparison of developmental stages of flowering shoots revealed delays in flower development for deep plants compared with shallow plants for all sites, demonstrating a consistent offset in reproductive phenology across depths. Our results suggest that differences in the timing of flowering may limit gene flow across seagrass meadows, with the potential for repeated genetic divergence in eelgrass populations spanning a depth gradient.

Success and impact metrics in science are based on a system that perpetuates sexist and racist “rewards” by prioritizing citations and impact factors. These metrics are flawed and biased against already marginalized groups and fail to accurately capture the breadth of individuals’ meaningful scientific impacts. We advocate shifting this outdated value system to advance science through principles of justice, equity, diversity, and inclusion. We outline pathways for a paradigm shift in scientific values based on multidimensional mentorship and promoting mentee well-being. These actions will require collective efforts supported by academic leaders and administrators to drive essential systemic change., This Essay argues that success and impact metrics in science are based on a system that perpetuates sexist and racist ‘rewards’ by prioritizing citations and impact factors; the authors advocate shifting this outdated value system to advance science through principles of justice, equity, diversity, and inclusion.

Este artículo contiene 7 páginas, 3 figuras, 1 tabla., The global distribution of primary production and consumption by humans (fisheries) is well-documented, but we have no map linking the central ecological process of consumption within food webs to temperature and other ecological drivers. Using standardized assays that span 105° of latitude on four continents, we show that rates of bait consumption by generalist predators in shallow marine ecosystems are tightly linked to both temperature and the composition of consumer assemblages. Unexpectedly, rates of consumption peaked at midlatitudes (25 to 35°) in both Northern and Southern Hemispheres across both seagrass and unvegetated sediment habitats. This pattern contrasts with terrestrial systems, where biotic interactions reportedly weaken away from the equator, but it parallels an emerging pattern of a subtropical peak in marine biodiversity. The higher consumption at midlatitudes was closely related to the type of consumers present, which explained rates of consumption better than consumer density, biomass, species diversity, or habitat. Indeed, the apparent effect of temperature on consumption was mostly driven by temperature-associated turnover in consumer community composition. Our findings reinforce the key influence of climate warming on altered species composition and highlight its implications for the functioning of Earth’s ecosystems., We acknowledge funding from the Smithsonian Institution and the Tula Foundation.

The issues mothers face in the academy have been discussed for decades. Routinely, new studies report significant differences between women and men at comparable career stages with respect to salary, service demands, publications, grant submissions, and overall funding rates. The COVID-19 pandemic is further exposing these inequalities as women scientists who are parenting while also engaging in a combination of academic related duties are falling further behind. COVID-19 is shaking the very foundations of our society and laying bare the many inequalities that defined our pre-COVID world. We can solve these inequities by investing strategically in creative solutions, thereby making the most of women’s contributions to scientific endeavors. Here we describe strategies that would make the academy more equitable for working mothers now and into the future. Importantly, while the data are clear that mothers are being disproportionally impacted by COVID-19, many groups could benefit from these same ideas. Now is the time to act. Rather than rebuilding what we once knew, let us be the architects of a new world.

Phenotypic variation within species can have community- and ecosystem-level effects. Such variation may be particularly important in ecosystem engineers, including many invasive species, because of the strong influence of these species on their surrounding communities and environment. We combined field surveys and glasshouse experiments to investigate phenotypic variation within the invasive common reed, Phragmites australis, among four estuarine source sites along the east coast of North America. Field surveys revealed variation in P. australis height and stem density among source sites. In a glasshouse environment, percent germination of P. australis seeds also varied across source sites. To test the degree to which phenotypic variation in P. australis reflected genetic or environmental differences, we conducted a glasshouse common garden experiment assessing the performance of P. australis seedlings from the four source sites across a salinity gradient. Populations maintained differences in morphology and growth in a common glasshouse environment, indicating a genetic component to the observed phenotypic variation. Despite this variation, experimentally increased porewater salinity consistently reduced P. australis stem density, height, and biomass. Differences in these morphological metrics are important because they are correlated with the impacts of invasive P. australis on the ecological communities it invades. Our results indicate that both colonization and spread of invasive P. australis will be dependent on the environmental and genetic context. Additional research on intraspecific variation in invasive species, particularly ecosystem engineers, will improve assessments of invasion impacts and guide management decisions in estuarine ecosystems.

Environmental perturbations can strongly affect community processes and ecosystem functions by acting primarily as a subsidy that increases productivity, a stress that decreases productivity, or both, with the predominant effect potentially shifting from subsidy to stress as the overall intensity of the perturbation increases. While perturbations are often considered along a single axis of intensity, they consist of multiple components (e.g., magnitude, frequency, and duration) that may not have equivalent stress and/or subsidy effects. Thus, different combinations of perturbation components may elicit community and ecosystem responses that differ in strength and/or direction (i.e., stress or subsidy) even if they reflect a similar overall perturbation intensity. To assess the independent and interactive effects of perturbation components, we experimentally manipulated the magnitude, frequency, and duration of wrack deposition, a common stress-subsidy in a variety of coastal systems. The effects of wrack perturbation on salt marsh community and ecosystem properties were assessed both in the short-term (at the end of a 12-week experimental manipulation) and long-term (6 months after the end of the experiment). In the short-term, plants and associated benthic invertebrates exhibited primarily stress-based responses to wrack perturbation. The extent of these stress effects on density of the dominant plant Spartina alterniflora, total plant percent cover, invertebrate abundance, and sediment oxygen availability were largely determined by perturbation duration. Yet, higher nitrogen content of Spartina, which indicates a subsidy effect of wrack, was influenced primarily by perturbation magnitude in the short-term. In the longer term, perturbation magnitude determined the extent of both stress and subsidy effects of wrack perturbation, with lower subordinate plant percent cover and snail density, and higher Spartina nitrogen content in high wrack biomass treatments. However, stress effects on the marsh community were generally less pronounced 6 months after the wrack perturbation, indicating capacity for recovery. Our results demonstrate that individual perturbation components can determine the degree to which its effects on the community elicit primarily stress- and/or subsidy-based responses. Further, the nature and extent of stress-subsidy effects can change over time, depending on species' relative ability to tolerate and/or recover from perturbation.

The rapid growth of the aquaculture industry to meet global seafood demand offers both risks and opportunities for resource management and conservation. In particular, hatcheries hold promise for stock enhancement and restoration, yet cultivation practices may lead to enhanced variation between populations at the expense of variation within populations, with uncertain implications for performance and resilience. To date, few studies have assessed how production techniques impact genetic diversity and population structure, as well as resultant trait variation in and performance of cultivated offspring. We collaborated with a commercial hatchery to produce multiple cohorts of the eastern oyster (Crassostrea virginica) from field-collected broodstock using standard practices. We recorded key characteristics of the broodstock (male : female ratio, effective population size), quantified the genetic diversity of the resulting cohorts, and tested their trait variation and performance across multiple field sites and experimental conditions. Oyster cohorts produced under the same conditions in a single hatchery varied almost twofold in genetic diversity. In addition, cohort genetic diversity was a significant positive predictor of oyster performance traits, including initial size and survival in the field. Oyster cohorts produced in the hatchery had lower within-cohort genetic variation and higher among-cohort genetic structure than adults surveyed from the same source sites. These findings are consistent with "sweepstakes reproduction" in oysters, even when manually spawned. A readily measured characteristic of broodstock, the ratio of males to females, was positively correlated with within-cohort genetic diversity of the resulting offspring. Thus, this metric may offer a tractable way both to meet short-term production goals for seafood demand and to ensure the capacity of hatchery-produced stock to achieve conservation objectives, such as the recovery of self-sustaining wild populations.

Functional trait variation within and across populations can strongly influence population, community, and ecosystem processes, but the relative contributions of genetic vs. environmental factors to this variation are often not clear, potentially complicating conservation and restoration efforts. For example, local adaptation, a particular type of genetic by environmental (G*E) interaction in which the fitness of a population in its own habitat is greater than in other habitats, is often invoked in management practices, even in the absence of supporting evidence. Despite increasing attention to the potential for G*E interactions, few studies have tested multiple populations and environments simultaneously, limiting our understanding of the spatial consistency in patterns of adaptive genetic variation. In addition, few studies explicitly differentiate adaptation in response to predation from other biological and environmental factors. We conducted a reciprocal transplant experiment of first-generation eastern oyster (Crassostrea virginica) juveniles from six populations across three field sites spanning 1000 km in the southeastern Atlantic Bight in both the presence and absence of predation to test for G*E variation in this economically valuable and ecologically important species. We documented significant G*E variation in survival and growth, yet there was no evidence for local adaptation. Condition varied across oyster cohorts: Offspring of northern populations had better condition than offspring from the center of our region. Oyster populations in the southeastern Atlantic Bight differ in juvenile survival, growth, and condition, yet offspring from local broodstock do not have higher survival or growth than those from farther away. In the absence of population-specific performance information, oyster restoration and aquaculture may benefit from incorporating multiple populations into their practices.

Genetic diversity can influence ecological processes throughout ontogeny, yet whether diversity at early life history stages is important in long-lived taxa with overlapping generations is unclear. Seagrass systems provide some of the best evidence for the ecological effects of genetic diversity among adult shoots, but we do not know if the genetic diversity of seeds and seedlings also influences seagrass ecology. We tested the effects of seagrass (Zostera marina) seed diversity and relatedness on germination success, seedling morphology, and seedling production by comparing experimental assemblages of seeds collected from single reproductive shoots (“monocultures”) to assemblages of seeds collected from multiple reproductive shoots (“polycultures”). There was no difference in seedling emergence, yet seedlings from polycultures had larger shoots above and below ground than seedlings from monocultures at the end of the one-year experiment. Genetic relatedness of the seedlings predicted some aspects of shoot morphology, with more leaves and longer roots and shoots at intermediate levels of relatedness, regardless of seed diversity. Our results suggest that studies of only adult stages may underestimate the importance of genetic diversity if the benefits at early life history stages continue to accrue throughout the life cycle. This article is protected by copyright. All rights reserved.

Latitudinal gradients in ecosystem patterns arise from complex interactions between biotic and abiotic forces operating at a range of spatial and temporal scales. Widespread invasive species, particularly invasive ecosystem engineers with large effects on their environment, may alter these gradients. We sampled 3–5 stands of the invasive common reed, Phragmites australis, in eight coastal wetlands ranging from Massachusetts (42°N) to South Carolina (32°N) to document geographic variation in P. australis primary production, associated plant and animal species diversity, and sediment carbon storage and to examine how local-, regional-, and large-scale environmental factors contribute to these patterns. Latitude best explained variation in P. australis density, but contrary to expectations, density increased with increasing latitude across our sites. Latitude also predicted macroinvertebrate species richness, which increased with latitude in a manner similar to P. australis density. In addition to latitude, P. australis leaf carbon:nitrogen ratios, distance to the open coast, and sediment oxygen levels were most important for explaining variation in P. australis production, as well as community (plant or animal species richness) and ecosystem (carbon storage) variables. The percent of developed land was positively associated with P. australis density, yet this variable had relatively low predictive power in our study. Our study provides an important biogeographic perspective for documenting and understanding variation in invasive P. australis that is fundamental both for managing the invasion and for understanding latitudinal gradients in ecosystem structure and function.

Climate change is causing shifts in the distribution and abundance of many species. Because species vary in the rate and degree of these shifts, novel transition zones have developed where new combinations of species overlap. If climate‐mediated range shifts result in greater diversity, transition communities could have enhanced resistance and/or resilience, particularly if the resident and colonizing species differ in their response to environmental change. The range expansion of the tropical black mangrove, Avicennia germinans, into salt marshes dominated by the temperate cordgrass, Spartina alterniflora, provides an opportunity to examine the responses of climate‐mediated transition zones to disturbance. We conducted a yearlong mesocosm experiment testing the effects of plant species identity and composition (A. germinans, S. alterniflora), as well as plant genotypic diversity (S. alterniflora only), on the response of coastal wetlands to oiling disturbance. Oil negatively impacted S. alterniflora and A. germinans both above‐ and belowground, though the timing of these effects varied, with S. alterniflora showing more immediate declines than A. germinans. As hypothesized, the magnitude of the oil effect was reduced in the mixed plant species treatment compared to the single species treatment for A. germinans survival (12% vs. 21% reduction) and belowground biomass (19% vs. 71% reduction). In addition, when exposed to oil, A. germinans crown area and volume were greater in the mixed species treatment compared to the single species treatment at the end of the experiment. However, we did not detect any benefit of mixed species communities or S. alterniflora genotypic diversity for the S. alterniflora response to oil. Our results suggest that transition habitats in the northern Gulf of Mexico where A. germinans and S. alterniflora co‐occur will be negatively impacted by future oiling events, but that they are no more susceptible, and perhaps slightly less so, than habitats dominated by either individual species.

The importance of intraspecific variation has emerged as a key question in community ecology, helping to bridge the gap between ecology and evolution. Although much of this work has focused on plant species, recent syntheses have highlighted the prevalence and potential importance of morphological, behavioral, and life history variation within animals for ecological and evolutionary processes. Many small-bodied consumers live on the plant that they consume, often resulting in host plant-associated trait variation within and across consumer species. Given the central position of consumer species within tritrophic food webs, such consumer trait variation may play a particularly important role in mediating trophic dynamics, including trophic cascades. In this study, we used a series of field surveys and laboratory experiments to document intraspecific trait variation in a key consumer species, the marsh periwinkle Littoraria irrorata, based on its host plant species (Spartina alterniflora or Juncus roemerianus) in a mixed species assemblage. We then conducted a 12-week mesocosm experiment to examine the effects of Littoraria trait variation on plant community structure and dynamics in a tritrophic salt marsh food web. Littoraria from different host plant species varied across a suite of morphological and behavioral traits. These consumer trait differences interacted with plant community composition and predator presence to affect overall plant stem height, as well as differentially alter the density and biomass of the two key plant species in this system. Whether due to genetic differences or phenotypic plasticity, trait differences between consumer types had significant ecological consequences for the tritrophic marsh food web over seasonal time scales. By altering the cascading effects of the top predator on plant community structure and dynamics, consumer differences may generate a feedback over longer time scales, which in turn influences the degree of trait divergence in subsequent consumer populations.

Stability contributes to the persistence of ecological communities, yet the interactions among different stabilizing forces are poorly understood. We assembled mesocosms with an algal resource and one to eight different clones of the consumer Daphnia ambigua and tracked algal and Daphnia abundances through time. We then fitted coupled ordinary differential equations (ODEs) to the consumer-resource time series. We show that variation in different components of stability (local stability and the magnitude of population fluctuations) across mesocosms arises through variation in life history traits and the functional processes represented by ODE model parameters. Local stability was enhanced by increased algal growth rate and Daphnia mortality and foraging rate. Population fluctuations were dampened by high Daphnia conversion efficiency and lower interaction strengths, low algal growth rate, high Daphnia death rate, and low Daphnia foraging. These results indicate that (1) stability in consumer-resource systems may arise through the net effect of multiple related stabilizing pathways and (2) different aspects of stability can vary independently and may respond in opposite directions to the same forces.

Latitudinal gradients in species interactions are widely cited as potential causes or consequences of global patterns of biodiversity. However, mechanistic studies documenting changes in interactions across broad geographic ranges are limited. We surveyed predation intensity on common prey (live amphipods and gastropods) in communities of eelgrass (Zostera marina) at 48 sites across its Northern Hemisphere range, encompassing over 37 degrees of latitude and four continental coastlines. Predation on amphipods declined with latitude on all coasts but declined more strongly along western ocean margins where temperature gradients are steeper. Whereas insitu water temperature at the time of the experiments was uncorrelated with predation, mean annual temperature strongly positively predicted predation, suggesting a more complex mechanism than simply increased metabolic activity at the time of predation. This large-scale biogeographic pattern was modified by local habitat characteristics; predation declined with higher shoot density both among and within sites. Predation rates on gastropods, by contrast, were uniformly low and varied little among sites. The high replication and geographic extent of our study not only provides additional evidence to support biogeographic variation in predation intensity, but also insight into the mechanisms that relate temperature and biogeographic gradients in species interactions. NSF BIO-OCE [1336206, 1336741, 1336905] info:eu-repo/semantics/publishedVersion

Summary Body size is of fundamental importance to the structure and function of natural systems, yet the factors selecting for certain body sizes are still not well understood. Resource supply levels clearly play a role in setting size, but in current theory, optimality functions for body size are not tied to the population dynamics that govern resource supply, minimizing our ability to understand how body size evolves in response to the ecological context. We integrated the supply-demand (SD) model of body size evolution with a model of predator–prey dynamics to create a dynamic SD model that describes predator body size variation through time. We tested the model with experimental data on body size and abundance dynamics in the Didinium–Paramecium predator–prey system. We used a new differential equation fitting approach along with independently estimated parameters to determine whether the model could simultaneously capture both abundance and body size dynamics. The dynamics were well described by the model, supporting the notion that body size changes to match bodily demand for resources with the available supply of resources. Surprisingly, despite the 10-fold variation in Didinium body size, we found that static model parameters were sufficient to describe the data, suggesting a lack of eco-evolutionary dynamics. A pressing need in ecology is to be able to predict changes in body size under novel scenarios, especially climate warming. The dynamic SD model does this by linking body size to the ecological context in an eco-evolutionary framework. Our approach expands our ability to understand rapid linked changes in traits and abundance.

Intraspecific diversity, particularly of foundation species, can significantly affect population, community, and ecosystem processes. Examining how genetic diversity relates to demographic traits provides a key mechanistic link from genotypic and phenotypic variation of taxa with complex life histories to their population dynamics. We conducted a field experiment to assess how two metrics of intraspecific diversity (cohort diversity, the number of independent juvenile cohorts created from different adult source populations, and genetic relatedness, genetic similarity among individuals within and across cohorts) affect the survivorship, growth, and recruitment of the foundation species Crassostrea virginica. To assess the effects of both cohort diversity and genetic relatedness on oyster demographic traits under different environmental conditions, we manipulated juvenile oyster diversity and predator exposure (presence/absence of a cage) at two sites differing in resource availability and predation intensity. Differences in predation pressure between sites overwhelmingly determined post-settlement survivorship of oysters. However, in the absence of predation (i.e., cage treatment), one or both metrics of intraspecific diversity, in addition to site, influenced long-term survivorship, growth, and recruitment. While both cohort diversity and genetic relatedness were negatively associated with long-term survivorship, genetic relatedness alone showed a positive association with growth and cohort diversity alone showed a positive association with recruitment. Thus, our results demonstrate that in the absence of predation, intraspecific diversity can affect multiple demographic traits of a foundation species, but the relative importance of these effects depends on the environmental context. Moreover, the magnitude and direction of these effects vary depending on the diversity metric, cohort diversity or genetic relatedness, suggesting that although they are inversely related in this system, each captures sufficiently different components of intraspecific diversity. Given the global loss of oyster reef habitat and rapid decline in oyster population size, our results are particularly relevant to management and restoration. In addition, aquaculture, which commonly excludes predators during early life history stages, may benefit from incorporation of oyster cohort diversity into standard practice.

Functional trait variation within and across populations can strongly influence population, community, and ecosystem processes, but the relative contributions of genetic vs. environmental factors to this variation are often not clear, potentially complicating conservation and restoration efforts. For example, local adaptation, a particular type of genetic by environmental (G*E) interaction in which the fitness of a population in its own habitat is greater than in other habitats, is often invoked in management practices, even in the absence of supporting evidence. Despite increasing attention to the potential for G*E interactions, few studies have tested multiple populations and environments simultaneously, limiting our understanding of the spatial consistency in patterns of adaptive genetic variation. In addition, few studies explicitly differentiate adaptation in response to predation from other biological and environmental factors. We conducted a reciprocal transplant experiment of first‐generation eastern oyster (Crassostrea virginica) juveniles from six populations across three field sites spanning 1000 km in the southeastern Atlantic Bight in both the presence and absence of predation to test for G*E variation in this economically valuable and ecologically important species. We documented significant G*E variation in survival and growth, yet there was no evidence for local adaptation. Condition varied across oyster cohorts: Offspring of northern populations had better condition than offspring from the center of our region. Oyster populations in the southeastern Atlantic Bight differ in juvenile survival, growth, and condition, yet offspring from local broodstock do not have higher survival or growth than those from farther away. In the absence of population‐specific performance information, oyster restoration and aquaculture may benefit from incorporating multiple populations into their practices.

At present, the disciplines of evolutionary biology and ecosystem science are weakly integrated. As a result, we have a poor understanding of how the ecological and evolutionary processes that create, maintain, and change biological diversity affect the flux of energy and materials in global biogeochemical cycles. The goal of this article was to review several research fields at the interfaces between ecosystem science, community ecology and evolutionary biology, and suggest new ways to integrate evolutionary biology and ecosystem science. In particular, we focus on how phenotypic evolution by natural selection can influence ecosystem functions by affecting processes at the environmental, population and community scale of ecosystem organization. We develop an eco-evolutionary model to illustrate linkages between evolutionary change (e. g. phenotypic evolution of producer), ecological interactions (e. g. consumer grazing) and ecosystem processes (e. g. nutrient cycling). We conclude by proposing experiments to test the ecosystem consequences of evolutionary changes.

List of contributors Preface Part I. Theory: 1. Theoretical perspectives on bottom-up and top-down interactions across ecosystems Shawn J. Leroux and Michel Loreau Part II. Ecosystems: 2. The spatio-temporal dynamics of trophic control in large marine ecosystems Kenneth T. Frank, Jonathan A. D. Fisher and William C. Leggett 3. Top-down and bottom-up interactions in freshwater ecosystems: emerging complexities Jason M. Taylor, Michael J. Vanni and Alexander S. Flecker 4. Top-down and bottom-up interactions determine tree and herbaceous layer dynamics in savannah grasslands A. Carla Staver and Sally Koerner 5. Bottom-up and top-down forces shaping wooded ecosystems: lessons from a cross-biome comparison Dries P. J. Kuijper, Mariska te Beest, Marcin Churski and Joris P. G. M. Cromsigt 6. Dynamic systems of exchange link trophic dynamics in freshwater and terrestrial food webs John L. Sabo and David Hoekman 7. Bottom-up and top-down interactions in coastal interface systems Jan P. Bakker, Karina J. Nielsen, Juan Alberti, Francis Chan, Sally D. Hacker, Oscar O. Iribarne, Dries P. J. Kuijper, Bruce A. Menge, Maarten Schrama and Brian R. Silliman Part III. Patterns and Processes: 8. Influence of plant defences and nutrients on trophic control of ecosystems Karin T. Burghardt and Oswald J. Schmitz 9. Interactive effects of plants, decomposers, herbivores, and predators on nutrient cycling Sarah E. Hobbie and Sebastien Villeger 10. The role of bottom-up and top-down interactions in determining microbial and fungal diversity and function Thomas W. Crowther and Hans-Peter Grossart 11. The question of scale in trophic ecology Lee A. Dyer, Tara J. Massad and Matthew L. Forister 12. The role of species diversity in bottom-up and top-down interactions Jerome J. Weis 13. Plant and herbivore evolution within the trophic sandwich Luis Abdala-Roberts and Kailen A. Mooney 14. Bottom-up and top-down interactions across ecosystems in an era of global change Kimberly J. La Pierre and Torrance C. Hanley Index.

Primers were developed for the amplification and sequencing of the mitochondrial control region of Galapagos land (Conolophus) and marine (Amblyrhynchus) iguanas. Sequences were obtained for four land iguana samples from two islands and for 28 marine iguana samples from three islands. A series of 70–80 bp tandem repeats adjacent to the control region are described and preliminary quantification of intra- and interspecific sequence divergence is included.

Summary Although mass and temperature are strong predictors of metabolic rates, there is considerable unexplained variation in metabolic rates both within and across species after body size and temperature are taken into account. Some of this variation may be due to changes in the rate of food intake with population density, as metabolism depends on the throughput of food to fuel biochemical reactions. Using data collected from the literature, we show that individual metabolic rates are negatively correlated with population density for a wide range of organisms including primary producers and consumers. Using new data for the zooplankter Daphnia ambigua, we also find genotypic variation in the relationship between metabolic rate and population density. The relationship between metabolic rate and population density generally follows a power law scaling, and within a population, density-correlated variation in metabolism can span two orders of magnitude. We suggest that density-dependent metabolic rates arise via competitive effects on foraging rates (both exploitation and interference competition), combined with an activity response to accommodate the resource constraint induced by competition. Standard ecological models predict the kind of density-dependent foraging patterns that could give rise to density-dependent metabolic rates, but this has generally not been investigated. Our results indicate that after body mass and temperature, population density represents an important third axis that may account for a large amount of unexplained variance in metabolic rates within and among species. The effect of population density on metabolism has implications for the scaling of metabolic rates from individuals to populations and the relative performance of species and genotypes and therefore also for community assembly and evolution.

It is becoming increasingly clear that intraspecific evolutionary divergence influences the properties of populations, communities and ecosystems. The different ecological impacts of phenotypes and genotypes may alter selection on many species and promote a cascade of ecological and evolutionary change throughout the food web. Theory predicts that evolutionary interactions across trophic levels may contribute to hypothesized feedbacks between ecology and evolution. However, the importance of ‘cascading evolutionary change’ in a natural setting is unknown. In lakes in Connecticut, USA, variation in migratory behaviour and feeding morphology of a fish predator, the alewife ( Alosa pseudoharengus ), drives life-history evolution in a species of zooplankton prey ( Daphnia ambigua ). Here we evaluated the reciprocal impacts of Daphnia evolution on ecological processes in laboratory mesocosms. We show that life-history evolution in Daphnia facilitates divergence in rates of population growth, which in turn significantly alters consumer-resource dynamics and ecosystem function. These experimental results parallel trends observed in lakes. Such results argue that a cascade of evolutionary change, which has occurred over contemporary timescales, alters community and ecosystem processes.

At present, the disciplines of evolutionary biology and ecosystem science are weakly integrated. As a result, we have a poor understanding of how the ecological and evolutionary processes that create, maintain, and change biological diversity affect the flux of energy and materials in global biogeochemical cycles. The goal of this article was to review several research fields at the interfaces between ecosystem science, community ecology and evolutionary biology, and suggest new ways to integrate evolutionary biology and ecosystem science. In particular, we focus on how phenotypic evolution by natural selection can influence ecosystem functions by affecting processes at the environmental, population and community scale of ecosystem organization. We develop an eco-evolutionary model to illustrate linkages between evolutionary change (e.g. phenotypic evolution of producer), ecological interactions (e.g. consumer grazing) and ecosystem processes (e.g. nutrient cycling). We conclude by proposing experiments to test the ecosystem consequences of evolutionary changes.

Background: Marine iguanas (Amblyrhynchus cristatus) inhabit the coastlines of large and small islands throughout the Galápagos archipelago, providing a rich system to study the spatial and temporal factors influencing the phylogeographic distribution and population structure of a species. Here, we analyze the microevolution of marine iguanas using the complete mitochondrial control region (CR) as well as 13 microsatellite loci representing more than 1200 individuals from 13 islands. Results CR data show that marine iguanas occupy three general clades: one that is widely distributed across the northern archipelago, and likely spread from east to west by way of the South Equatorial current, a second that is found mostly on the older eastern and central islands, and a third that is limited to the younger northern and western islands. Generally, the CR haplotype distribution pattern supports the colonization of the archipelago from the older, eastern islands to the younger, western islands. However, there are also signatures of recurrent, historical gene flow between islands after population establishment. Bayesian cluster analysis of microsatellite genotypes indicates the existence of twenty distinct genetic clusters generally following a one-cluster-per-island pattern. However, two well-differentiated clusters were found on the easternmost island of San Cristóbal, while nine distinct and highly intermixed clusters were found on youngest, westernmost islands of Isabela and Fernandina. High mtDNA and microsatellite genetic diversity were observed for populations on Isabela and Fernandina that may be the result of a recent population expansion and founder events from multiple sources. Conclusions While a past genetic study based on pure F ST analysis suggested that marine iguana populations display high levels of nuclear (but not mitochondrial) gene flow due to male-biased dispersal, the results of our sex-biased dispersal tests and the finding of strong genetic differentiation between islands do not support this view. Therefore, our study is a nice example of how recently developed analytical tools such as Bayesian clustering analysis and DNA sequence-based demographic analyses can overcome potential biases introduced by simply relying on F ST estimates from markers with different inheritance patterns.