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Showing papers in "Ecological Monographs in 2015"


Journal ArticleDOI
TL;DR: This guide serves as a reference for ecologists using Bayesian methods, so that they can better understand their options and can make an informed choice that is best aligned with their goals for inference.
Abstract: The steady upward trend in the use of model selection and Bayesian methods in ecological research has made it clear that both approaches to inference are important for modern analysis of models and data. However, in teaching Bayesian methods and in working with our research colleagues, we have noticed a general dissatisfaction with the available literature on Bayesian model selection and multimodel inference. Students and researchers new to Bayesian methods quickly find that the published advice on model selection is often preferential in its treatment of options for analysis, frequently advocating one particular method above others. The recent appearance of many articles and textbooks on Bayesian modeling has provided welcome background on relevant approaches to model selection in the Bayesian framework, but most of these are either very narrowly focused in scope or inaccessible to ecologists. Moreover, the methodological details of Bayesian model selection approaches are spread thinly throughout the literature, appearing in journals from many different fields. Our aim with this guide is to condense the large body of literature on Bayesian approaches to model selection and multimodel inference and present it specifically for quantitative ecologists as neutrally as possible. We also bring to light a few important and fundamental concepts relating directly to model selection that seem to have gone unnoticed in the ecological literature. Throughout, we provide only a minimal discussion of philosophy, preferring instead to examine the breadth of approaches as well as their practical advantages and disadvantages. This guide serves as a reference for ecologists using Bayesian methods, so that they can better understand their options and can make an informed choice that is best aligned with their goals for inference.

662 citations


Journal ArticleDOI
TL;DR: In this article, the effects of resource stoichiometry on soil microorganisms and decomposition, specifically on the structure and function of the soil food web, have been investigated, focusing on heterotrophic microbial communities.
Abstract: Elemental stoichiometry constitutes an inherent link between biogeochemistry and the structure and processes within food webs, and thus is at the core of ecosystem functioning. Stoichiometry allows for spanning different levels of biological organization, from cellular metabolism to ecosystem structure and nutrient cycling, and is therefore particularly useful for establishing links between different ecosystem compartments. We review elemental carbon : nitrogen : phosphorus (C:N:P) ratios in terrestrial ecosystems (from vegetation, leaf litter, woody debris, and dead roots, to soil microbes and organic matter). While the stoichiometry of the plant, litter, and soil compartments of ecosystems is well understood, heterotrophic microbial communities, which dominate the soil food web and drive nutrient cycling, have received increasing interest in recent years. This review highlights the effects of resource stoichiometry on soil microorganisms and decomposition, specifically on the structure and function of h...

660 citations


Journal ArticleDOI
TL;DR: A general causal theory is presented to explain why human societies gained the capacity to globally alter the patterns, processes, and dynamics of ecology and how these anthropogenic alterations unfold over time and space as societies themselves change over human generational time.
Abstract: Humans, unlike any other multicellular species in Earth's history, have emerged as a global force that is transforming the ecology of an entire planet. It is no longer possible to understand, predict, or successfully manage ecological pattern, process, or change without understanding why and how humans reshape these over the long term. Here, a general causal theory is presented to explain why human societies gained the capacity to globally alter the patterns, processes, and dynamics of ecology and how these anthropogenic alterations unfold over time and space as societies themselves change over human generational time. Building on existing theories of ecosystem engineering, niche construction, inclusive inheritance, cultural evolution, ultrasociality, and social change, this theory of anthroecological change holds that sociocultural evolution of subsistence regimes based on ecosystem engineering, social specialization, and non-kin exchange, or “sociocultural niche construction,” is the main cause of both the long-term upscaling of human societies and their unprecedented transformation of the biosphere. Human sociocultural niche construction can explain, where classic ecological theory cannot, the sustained transformative effects of human societies on biogeography, ecological succession, ecosystem processes, and the ecological patterns and processes of landscapes, biomes, and the biosphere. Anthroecology theory generates empirically testable hypotheses on the forms and trajectories of long-term anthropogenic ecological change that have significant theoretical and practical implications across the subdisciplines of ecology and conservation. Though still at an early stage of development, anthroecology theory aligns with and integrates established theoretical frameworks including social–ecological systems, social metabolism, countryside biogeography, novel ecosystems, and anthromes. The “fluxes of nature” are fast becoming “cultures of nature.” To investigate, understand, and address the ultimate causes of anthropogenic ecological change, not just the consequences, human sociocultural processes must become as much a part of ecological theory and practice as biological and geophysical processes are now. Strategies for achieving this goal and for advancing ecological science and conservation in an increasingly anthropogenic biosphere are presented.

397 citations


Journal ArticleDOI
TL;DR: Using multispecies population models fit to long-term demographic data for common, co-occurring species in five grassland and shrubland plant communities in western North America, the strength of stabilizing niche differences and average fitness differences is estimated.
Abstract: Niche differences and average fitness differences jointly determine coexistence. However, little empirical information about the magnitude of these two mechanisms is available. Using multispecies population models fit to long-term demographic data for common, co-occurring species in five grassland and shrubland plant communities in western North America, we estimated the strength of stabilizing niche differences and average fitness differences. In all five communities, both pairwise and full community comparisons showed evidence for strong stabilizing mechanisms and relatively small average fitness differences. For a total of 17 species pairs, a measure of niche differences based on simulations of invasion growth rates ranged from 0.59 to 0.93 with a mean of 0.81, where 0 indicates complete niche overlap and 1 indicates zero niche overlap. A corresponding measure of average fitness differences ranged from 1.02 to 2.54 with a mean of 1.53, where 1 indicates identical fitness and a value of 2 indicates a fo...

154 citations


Journal ArticleDOI
TL;DR: In this article, the authors used an information-theoretic approach to rank competing models in which fragmentation, discharge magnitude, and percentage of time streams had zero flow were included to predict effects of environmental alterations on the distribution of fishes belonging to different reproductive guilds.
Abstract: Biodiversity in stream networks is threatened globally by interactions between habitat fragmentation and altered hydrologic regimes. In the Great Plains of North America, stream networks are fragmented by >19 000 anthropogenic barriers, and flow regimes are altered by surface water retention and groundwater extraction. We documented the distribution of anthropogenic barriers and dry stream segments in five basins covering the central Great Plains to assess effects of broad-scale environmental change on stream fish community structure and distribution of reproductive guilds. We used an information-theoretic approach to rank competing models in which fragmentation, discharge magnitude, and percentage of time streams had zero flow (a measure of desiccation) were included to predict effects of environmental alterations on the distribution of fishes belonging to different reproductive guilds. Fragmentation caused by anthropogenic barriers was most common in the eastern Great Plains, but stream desiccation beca...

149 citations


Journal ArticleDOI
TL;DR: An association between high-quality soil C and fungi emerges from an experiment where litter and root inputs are experimentally manipulated, finding no support for the hypothesized differences between detrital food webs dominated by bacteria compared to those dominated by fungi.
Abstract: Resolving fungal and bacterial groups within the microbial decomposer community is thought to capture disparate life strategies for soil microbial decomposers, associating bacteria with an r-selected strategy for carbon (C) and nutrient use, and fungi with a K-selected strategy. Additionally, food-web model-based work has established a widely held belief that the bacterial decomposer pathway in soil supports high turnover rates of easily available substrates, while the slower fungal-dominated decomposition pathway supports the decomposition of more complex organic material, thus characterizing the biogeochemistry of the ecosystem. We used a field experiment, the Detritus Input and Removal Treatments, or DIRT, experiment (Harvard Forest Long-Term Ecological Research Site, USA) where litter and root inputs (control, no litter, double litter, or no tree roots) have been experimentally manipulated during 23 years, generating differences in soil C quality. We hypothesized (1) that delta C-13 enrichment would decrease with higher soil C quality and that a higher C quality would favor bacterial decomposers, (2) that the C mineralized in fungal-dominated treatments would be of lower quality and also depleted in delta C-13 relative to bacterial-dominated high-quality soil C treatments, and (3) that higher C mineralization along with higher gross N mineralization rates would occur in bacterial-dominated treatments compared with more fungal-dominated treatments. The DIRT treatments resulted in a gradient of soil C quality, as shown by up to 4.5-fold differences between the respiration per soil C between treatments. High-quality C benefited fungal dominance, in direct contrast with our hypothesis. Further, there was no difference between the delta(CO2)-C-13 produced by a fungal compared with a bacterial-dominated decomposer community. There were differences in C and N mineralization between DIRT treatments, but these were not related to the relative dominance of fungal and bacterial decomposers. Thus we find no support for the hypothesized differences between detrital food webs dominated by bacteria compared to those dominated by fungi. Rather, an association between high-quality soil C and fungi emerges from our results. Consequently there is a need to revise our basic understanding for microbial communities and the processes they regulate in soil. (Less)

136 citations


Journal ArticleDOI
TL;DR: Focusing on the comprehensive information stored in aquatic and terrestrial organism hard parts, a series of increasingly complex hierarchical models are developed to explore spatial and temporal sources of growth variation, ranging in resolution from within individuals to across a species.
Abstract: Growth is a fundamental biological process, driven by a multitude of intrinsic (within-individual) and extrinsic (environmental) factors, that underpins individual fitness and population demographics. Focusing on the comprehensive information stored in aquatic and terrestrial organism hard parts, we develop a series of increasingly complex hierarchical models to explore spatial and temporal sources of growth variation, ranging in resolution from within individuals to across a species. We apply this modeling framework to an extensive data set of otolith increment measurements from tiger flathead (Platycephalus richardsoni), a demersal commercially exploited fish that inhabits the warming waters of southeast Australia. We recreated growth histories (biochronology) up to four decades in length from seven fishing areas spanning this species' range. The dominant pattern in annual growth was an age-dependent, allometric decline that varied among individuals, sexes, fishing areas, years, and cohorts. We found ev...

122 citations


Journal ArticleDOI
TL;DR: In this article, the authors show that tube-dwelling invertebrates play a central role in controlling water column nutrient pools, and hence water quality and trophic state.
Abstract: There is ample evidence that tube-dwelling invertebrates such as chironomids significantly alter multiple important ecosystem functions, particularly in shallow lakes. Chironomids pump large water volumes, and associated suspended and dissolved substances, through the sediment and thereby compete with pelagic filter feeders for particulate organic matter. This can exert a high grazing pressure on phytoplankton, microorganisms, and perhaps small zooplankton and thus strengthen benthic-pelagic coupling. Furthermore, intermittent pumping by tube-dwelling invertebrates oxygenates sediments and creates a dynamic, three-dimensional mosaic of redox conditions. This shapes microbial community composition and spatial distribution, and alters microbe-mediated biogeochemical functions, which often depend on redox potential. As a result, extended hotspots of element cycling occur at the oxic-anoxic interfaces, controlling the fate of organic matter and nutrients as well as fluxes of nutrients between sediments and water. Surprisingly, the mechanisms and magnitude of interactions mediated by these organisms are still poorly understood. To provide a synthesis of the importance of tube-dwelling invertebrates, we review existing research and integrate previously disregarded functional traits into an ecosystem model. Based on existing research and our models, we conclude that tube-dwelling invertebrates play a central role in controlling water column nutrient pools, and hence water quality and trophic state. Furthermore, these tiny ecosystem engineers can influence the thresholds that determine shifts between alternate clear and turbid states of shallow lakes. The large effects stand in contrast to the conventional limnological paradigm emphasizing predominantly pelagic food webs. Given the vast number of shallow lakes worldwide, benthic invertebrates are likely to be relevant drivers of biogeochemical processes at regional and global scales, thereby mediating feedback mechanisms linked to climate change.

118 citations


Journal ArticleDOI
TL;DR: An exclusive definition of keystone species is used, based on the original concept ofKeystone predator, and a new functional index of keystoneness (KS) is derived from an ecosystem-modeling approach, directly applicable to marine food webs, and may be adapted to other (freshwater or terrestrial) systems.
Abstract: Various definitions and indices have been proposed in the literature to identify keystone species. In this study, we intended to make the concept of keystone species operational for marine biodiversity conservation. We used an exclusive definition of keystone species, based on the original concept of keystone predator, and derived a new functional index of keystoneness (KS) from an ecosystem-modeling approach. First, several KS indices were formulated, by combining measures of the mixed-trophic impact (MTI) and biomass of species. Then, a meta-analysis was performed, based on 101 published Ecopath food-web models, selected with a scoring method, and representative of the variety of marine ecosystems worldwide. The indices were applied to the models, and two statistical methods were compared to select the most promising KS index. Rank correlation tests were performed to assess the balance between the contribution of the impact and biomass components to the different KS indices. In addition, a classification tree was implemented, based on ecosystem-specific thresholds applied to the latter species traits, and used to confirm the identified keystone species. The selected index obtained the highest number of models with positive results from both the rank correlation tests and the classification tree. We also demonstrated the limitations of existing KS indices previously applied in the literature. Species were ranked according to their estimates of keystoneness with the selected KS index, so that potential keystone species were quantitatively identified in the 101 modeled food webs. The standardized modeling approach allowed for a comparison of the identified keystone species across models: cartilaginous fishes and toothed whales obtained the highest occurrences. Finally, the selected KS index was applied to the well-known case study of Prince William Sound (Alaska, USA). Potentially significant anthropogenic (fishing) impacts on keystone species were also considered and discussed. The operational methodology presented is directly applicable to marine food webs, and may be adapted to other (freshwater or terrestrial) systems.

118 citations


Journal ArticleDOI
TL;DR: In this paper, the authors examined changes in plant attributes, soil abiotic characteristics, and the soil microbial community in response to mowing (M), dung and urine addition (DU), simulated trampling (T), and their combinations by conducting a 3yr experiment in a steppe ecosystem in Inner Mongolia, China.
Abstract: Grazing can directly or indirectly influence carbon (C) inputs, turnover, and retention in grassland soil. However, relative to the plant response to grazing, belowground biota and process responses are more complex and often do not correlate with the aboveground responses. Ungulate grazing involves three mechanisms; defoliation (removal of plant shoot tissue), dung and urine return, and trampling. An evaluation of the relative roles of these mechanisms and their combinations in grazing can explain the causes of changes in grasslands, thereby explaining soil C sequestration in a steppe ecosystem. In this study, we examined changes in plant attributes, soil abiotic characteristics, and the soil microbial community in response to mowing (M), dung and urine addition (DU), simulated trampling (T), and their combinations by conducting a 3-yr experiment in a steppe ecosystem in Inner Mongolia, China. Most of the variation in the grazing effects on grasslands was explained by defoliation through decreased plant ...

115 citations


Journal ArticleDOI
TL;DR: This framework is proposed as a foundation for building more realistic connections between a population's use of space and its subsequent dynamics (and hence a contribution to the ongoing efforts to estimate a species' critical habitat and fundamental niche) and can be generalized to include a diverse range of biological considerations.
Abstract: Although classical ecological theory (e.g., on ideal free consumers) recognizes the potential effect of population density on the spatial distribution of animals, empirical species distribution models assume that species–habitat relationships remain unchanged across a range of population sizes. Conversely, even though ecological models and experiments have demonstrated the importance of spatial heterogeneity for the rate of population change, we still have no practical method for making the connection between the makeup of real environments, the expected distribution and fitness of their occupants, and the long-term implications of fitness for population growth. Here, we synthesize several conceptual advances into a mathematical framework using a measure of fitness to link habitat availability/selection to (density-dependent) population growth in mobile animal species. A key feature of this approach is that it distinguishes between apparent habitat suitability and the true, underlying contribution of a habitat to fitness, allowing the statistical coefficients of both to be estimated from multiple observation instances of the species in different environments and stages of numerical growth. Hence, it leverages data from both historical population time series and snapshots of species distribution to predict population performance under environmental change. We propose this framework as a foundation for building more realistic connections between a population's use of space and its subsequent dynamics (and hence a contribution to the ongoing efforts to estimate a species' critical habitat and fundamental niche). We therefore detail its associated definitions and simplifying assumptions, because they point to the framework's future extensions. We show how the model can be fit to data on species distributions and population dynamics, using standard statistical methods, and we illustrate its application with an individual-based simulation. When contrasted with nonspatial population models, our approach is better at fitting and predicting population growth rates and carrying capacities. Our approach can be generalized to include a diverse range of biological considerations. We discuss these possible extensions and applications to real data.

Journal ArticleDOI
TL;DR: Overall, there is little (if any) evidence for negative effects of old age on tree-level productivity in either Sequoia or Sequoiadendron, and both species are just as responsive to environmental changes as young trees.
Abstract: As the only species exceeding 90 m in height and 2000 years of age, Sequoia sempervirens and Sequoiadendron giganteum provide the optimal platform upon which to examine interactions among tree structure, age, and growth. We climbed 140 trees in old-growth redwood forests across California, USA, spanning a broad range of sizes and including the tallest, largest, and oldest known living individuals (i.e., 115.86 vs. 96.29 m tall, 424 vs. 582 Mg aboveground dry mass, and 2510 vs. 3240 years old for Sequoia and Sequoiadendron, respectively). We used a combination of direct measurements, hierarchical sampling, and dendrochronology to quantify tree structure and annual growth increments through old age. We also developed equations to predict aboveground attributes of standing redwoods via ground-based measurements. Compared to Sequoia, Sequoiadendron develops thicker bark on lower trunks, provisions leaves with more sapwood, and delays heartwood production throughout the crown. Main trunk wood volume growth (up to 1.6 vs. 0.9 m3/yr), aboveground biomass growth (up to 0.77 vs. 0.45 Mg/yr), and aboveground growth efficiency (0.55 ± 0.04 vs. 0.22 ± 0.01 kg annual growth per kg leaves, mean ± SE) are all higher in Sequoia. Two independent dimensions of structure—size and aboveground vigor—are the strongest predictors of tree-level productivity in both species. A third dimension, relative trunk size, is a significant predictor of growth in Sequoia such that trees with relatively large main trunks compared to their crowns produce more wood annually. Similar-size trees grow at similar rates regardless of latitude or elevation in tall forests of each species. Recent annual growth increments are higher than in the past for the majority of trees, and old trees are just as responsive to environmental changes as young trees. Negative growth–age relationships in previous centuries and positive growth–age relationships in recent decades reflect sampling bias and shifting disturbance regimes. Overall, we find little (if any) evidence for negative effects of old age on tree-level productivity in either species. Except for recovery periods following temporary reductions in crown size, annual increments of wood volume and biomass growth increase as redwoods enlarge with age until extrinsic forces cause tree death.

Journal ArticleDOI
TL;DR: In this paper, the authors quantified variation in a number of functional traits in 11 species of epiphytes and hemiepiphyte in a Costa Rican tropical montane cloud forest.
Abstract: Tropical montane cloud forests (TMCFs) inhabit regions rich in biodiversity that play an important role in the local and regional water cycle. Canopy plants such as epiphytes and hemiepiphytes are an important component of the biodiversity in the TMCF and therefore play a significant role in the carbon, nutrient, and water cycles. With only partial or no access to resources on the ground, canopy plants may be vulnerable to changes in climate that increase canopy temperatures and decrease atmospheric humidity or precipitation inputs. Despite their importance in the TMCF, little is known about variation in functional strategies relating to drought avoidance or drought tolerance of canopy plants. In this study, we quantified variation in a number of functional traits in 11 species of epiphytes and hemiepiphytes in a Costa Rican TMCF. We also generated pressure–volume and xylem vulnerability curves that we used as indicators of drought tolerance. In addition, we hand-sectioned fresh leaves and examined cross ...

Journal ArticleDOI
TL;DR: The chemical defenses of insect herbivores, on average, were effective against generalist predators, not effective against specialist predators and generalist parasitoids, and increased the risk of parasitism by specialist Parasitoids.
Abstract: The evolution of defensive traits and strategies depends on the intensity of selection imposed by natural enemies and on the fitness costs of defenses against these enemies. We tested several hypotheses about the evolution of chemical defenses in plant-feeding insects using a meta-analysis. We analyzed the effectiveness (in terms of prey survival; 159 publications) and costs (in terms of reduction in performance due to defense production; 33 publications) of chemical defenses in various prey-predator systems (140 herbivore species and 124 enemy species). The chemical defenses of insect herbivores, on average, were effective against generalist predators, not effective against specialist predators and generalist parasitoids, and increased the risk of parasitism by specialist parasitoids. The defenses were more effective against vertebrate than against invertebrate predators and most effective against birds. Defensive compounds synthesized de novo and derived from the herbivore's food plants did not differ i...

Journal ArticleDOI
TL;DR: In this paper, a hierarchical meta-ecosystem model is proposed to predict local community responses to connectivity over multiple oceanographic spatial scales, defined as macro-, meso-, and local scale (100s of m).
Abstract: Ecosystems are shaped by processes occurring and interacting over multiple temporal and spatial scales. Theory suggests such complexity can be simplified by focusing on processes sharing the same scale as the pattern of interest. This scale-dependent approach to studying communities has been challenged by multiscale meta-ecosystem theory, which recognizes that systems are interconnected by the movement of “ecological subsidies” and suggests that cross-scale feedbacks between local and regional processes can be equally important for understanding community structure. We reconcile these two perspectives by developing and testing a hierarchical meta-ecosystem model. The model predicts local community responses to connectivity over multiple oceanographic spatial scales, defined as macro- (100s of km), meso- (10s of km), and local scale (100s of m). It assumes that local communities occur in distinct regions and that connectivity effects are strongest among local sites. Predictions are that if macroscale proce...

Journal ArticleDOI
TL;DR: A general mathematical framework to represent soil organic matter dynamics, expressed in the language of dynamical systems and generalizes previous modeling approaches is proposed, which allows for the study of general properties of groups of models such as their qualitative behavior, timescale of application, and their dynamic stability.
Abstract: We propose here a general mathematical framework to represent soil organic matter dynamics. This framework is expressed in the language of dynamical systems and generalizes previous modeling approaches. It is based on a set of six basic principles about the decomposition of soil organic matter: (1) mass balance, (2) substrate dependence of decomposition, (3) heterogeneity of the speed of decay, (4) internal transformations of organic matter, (5) environmental variability effects, and (6) substrate interactions. We show how the majority of models previously proposed are special cases of this general model. This approach provides tools to classify models according to the main principles or concepts they include. It also helps to identify a priori the general behavior of different models or groups of models. Another important characteristic of the proposed mathematical representation is the possibility to develop particular models at any level of detail. This characteristic is described as a modeling hierarchy, in which a general model of a high degree of abstraction can accommodate specific realizations of model structure for specific modeling objectives. This framework also allows us to study general properties of groups of models such as their qualitative behavior, timescale of application, and their dynamic stability. For instance, we find conditions under which models are asymptotically stable, i.e., converge to a stable steady state in the long term, but may approach this state with or without oscillations. We also expand the concept of dynamic stability for models that include time dependencies and do not converge to a fixed steady state, but rather to a region of stability in the state-space. As an example of the application of the concept of dynamic stability, we show how this framework helps to explain the acclimation of soil respiration fluxes in soil-warming experiments.

Journal ArticleDOI
TL;DR: It is found that changes in the frequency of extreme events may strongly impact persistence of Southern Fulmar populations and ESICs strongly affect fitness components and act as potentially important agents of natural selection of life histories related to intrinsic quality and intermittent breeding.
Abstract: Extreme climatic conditions and their ecological impacts are currently emerging as critical features of climate change. We studied extreme sea ice condition (ESIC) and found it impacts both life-history traits and population dynamics of an Antarctic seabird well beyond ordinary variability. The Southern Fulmar (Fulmarus glacialoides) is an ice-dependent seabird, and individuals forage near the ice edge. During an extreme unfavorable year (when sea ice area is reduced and distance between ice edge and colony is high), observed foraging trips were greater in distance and duration. As a result, adults brought less food to their chicks, which fledged in the poorest body condition. During such unfavorable years, breeding success was extremely low and population growth rate (λ) was greatly reduced. The opposite pattern occurred during extreme favorable years. Previous breeding status had a strong influence on life-history traits and population dynamics, and their responses to extreme conditions. Successful breeders had a higher chance of breeding and raising their chick successfully during the following breeding season as compared to other breeding stages, regardless of environmental conditions. Consequently, they coped better with unfavorable ESIC. The effect of change in successful breeder vital rates on λ was greater than for other stages' vital rates, except for pre-breeder recruitment probabilities, which most affected λ. For environments characterized by ordinary sea ice conditions, interindividual differences were more likely to persist over the life of individuals and randomness in individual pathways was low, suggesting individual heterogeneity in vital rates arising from innate or acquired phenotypic traits. Additionally, unfavorable ESIC tended to exacerbate individual differences in intrinsic quality, expressed through differences in reproductive status. We discuss the strong effects of ESIC on Southern Fulmar life-history traits in an evolutionary context. ESICs strongly affect fitness components and act as potentially important agents of natural selection of life histories related to intrinsic quality and intermittent breeding. In addition, recruitment is a highly plastic trait that, if heritable, could have a critical role in evolution of life histories. Finally, we find that changes in the frequency of extreme events may strongly impact persistence of Southern Fulmar populations.

Journal ArticleDOI
TL;DR: The results show that the Climatic Variability Hypothesis is supported, even in taxa that do not exhibit a traditional Rapoport Effect, due to complex, non-unidirectional climatic gradients in the study area, and highlight the strong impact of climatic variability on species' physiological tolerances and their associated geographic distributions.
Abstract: The trend of increasing latitudinal range sizes of species towards higher latitudes, known as Rapoport's Rule, has been highly controversial in the literature since it was first proposed by Stevens in 1989. We contend that the question of interest is not whether general global patterns occur, nor whether they support or refute Rapoport's Rule, but whether the mechanism thought to underlie such patterns, the Climatic Variability Hypothesis, is supported. The Climatic Variability Hypothesis suggests that taxa originating from environmentally variable habitats, such as those at high latitudes and altitudes, should evolve wider environmental tolerances, and consequently establish wider distributions along climate gradients than taxa originating from relatively stable habitats. We applied a novel approach, incorporating measures of temperature variability across habitats within species' ranges into models of range size distributions, to determine whether the Climatic Variability Hypothesis applied to three clades of medium-sized ectotherms (lizards) distributed over Australia. Our results show that the Climatic Variability Hypothesis is supported, even in taxa that do not exhibit a traditional Rapoport Effect, due to complex, non-unidirectional climatic gradients in our study area. The results highlight the strong impact of climatic variability on species' physiological tolerances and their associated geographic distributions.

Journal ArticleDOI
TL;DR: This study shows that, despite being small, this percentage of energy stored during the parasitoid development has a great impact on adult fitness, the loss of which cannot be compensated for by a rich adult environment.
Abstract: Alterations of the amount and quality of food consumed during ontogeny can affect different life-history traits, such as growth rate, developmental time, survival, adult size, and fitness. Understanding the dynamics of such metabolic and energetic pathways and investments is particularly challenging in the case of holometabolous insects due to their strikingly different life stages. We show how whole life-cycle energy and mass budgets can be achieved for holometabolic insects through dynamic energy budget (DEB) theory, permitting the fate of acquired and stored nutrients to be followed over a complete life-cycle. We applied the DEB theory to model the whole life-cycle energetics of an endoparasitic wasp, Venturia canescens (Hymenoptera: Ichneumonidae). Data on embryo, larval, and pupal dry mass, imago longevity, and fecundity were used for assessing the goodness of fit of the model. Our model predicted the growth curves of the larval and pupal stages, the number of eggs laid by the imago through time, and lifespan events, such as the different developmental times of the parasitoid. The model enabled us to distinguish and follow the energy invested in eggs through income and capital reserves. The mechanisms leading to the double costs of being small (a shorter life under starving conditions and fewer eggs) were identified by running the model for varying amounts of food eaten early in life, according to host sizes. The final larval instar harvests around 60 times the energy of a recently hatched larva. Around 90% of this energy is then used during pupation to build the structure of the imago and to pay maintenance. Imagoes, therefore, emerge with only a small percentage of the energy stored by the last instar larvae. Our study shows that, despite being small, this percentage of energy stored during the parasitoid development has a great impact on adult fitness, the loss of which cannot be compensated for by a rich adult environment. Our model is generic and has applications for a wide range of applied and theoretical questions about insect energetics, from population dynamics in multitrophic systems to responses to climate change and life-history strategies.

Journal ArticleDOI
TL;DR: In this article, the authors constructed a Bayesian state-space model to reveal the influence of brucellosis on the Yellowstone bison population and found that a frequency-dependent model was superior to a densitydependent model in predicting out-of-sample observations of horizontal transmission probability.
Abstract: The bison (Bison bison) of the Yellowstone ecosystem, USA, exemplify the difficulty of conserving large mammals that migrate across the boundaries of conservation areas. Bison are infected with brucellosis (Brucella abortus) and their seasonal movements can expose livestock to infection. Yellowstone National Park has embarked on a program of adaptive management of bison, which requires a model that assimilates data to support management decisions. We constructed a Bayesian state-space model to reveal the influence of brucellosis on the Yellowstone bison population. A frequency-dependent model of brucellosis transmission was superior to a density-dependent model in predicting out-of-sample observations of horizontal transmission probability. A mixture model including both transmission mechanisms converged on frequency dependence. Conditional on the frequency-dependent model, brucellosis median transmission rate was 1.87 yr−1. The median of the posterior distribution of the basic reproductive ratio (R0) was...

Journal ArticleDOI
TL;DR: New randomization methods are introduced that incorporate sampling variability encompassing the entire length of the rarefaction curve and allow for statistical comparison of i ≥2 individual-based, sample- based, or coverage-basedRarefaction curves.
Abstract: The statistical framework of rarefaction curves and asymptotic estimators allows for an effective standardization of biodiversity measures. However, most statistical analyses still consist of point comparisons of diversity estimators for a particular sampling level. We introduce new randomization methods that incorporate sampling variability encompassing the entire length of the rarefaction curve and allow for statistical comparison of i ≥2 individual-based, sample-based, or coverage-based rarefaction curves. These methods distinguish between two distinct null hypotheses: the ecological null hypothesis (H0eco) and the biogeographical null hypothesis (H0biog). H0eco states that the i samples were drawn from a single assemblage, and any differences among them in species richness, composition, or relative abundance reflect only sampling effects. H0biog states that the i samples were drawn from assemblages that differ in their species composition but share similar species richness and species abundance distri...

Journal ArticleDOI
TL;DR: In this paper, fire scars, stand structure, and >4300 tree ages across two 1340-ha landscapes (Williams Creek and Squaretop Mountain) that span the environmental gradient of montane mixed-conifer and aspen forests were sampled.
Abstract: Mixed-severity fire regimes may be the most extensive yet poorly understood fire regimes of western North America. Understanding their long-term spatiotemporal dynamics is central to debates regarding altered fire regimes and the need for restoration in the context of changing climate and nearly a century of active fire suppression. However, the complexity of fire patterns and forest stand and landscape structures characteristic of mixed-severity regimes poses a substantial challenge to understanding their long-term dynamics. In this study, we develop analysis methods aimed at understanding the fire-driven forest dynamics of mixed-severity systems and apply them in the San Juan Mountains of southwestern Colorado. We sampled fire scars, stand structure, and >4300 tree ages across two 1340-ha landscapes (Williams Creek and Squaretop Mountain) that span the environmental gradient of montane mixed-conifer and aspen forests. New approaches were applied to identify pulses of tree recruitment, evaluate climate and fire as potential drivers of synchronous recruitment pulses, and combine fire scar and recruitment data to reconstruct fires. The reconstructions provided detailed fire history for each stand, which in turn was used to develop a fire-severity metric, compare fire frequency and severity by forest type, and develop a simulation procedure to evaluate the degree to which tree regeneration depended on fire by species within each forest type. Twenty fires were reconstructed since 1685 at Williams Creek and 13 fires since 1748 at Squaretop Mountain. Patterns of fire severity varied within each fire and over successive events, including high-severity patches of hundreds of hectares in both study areas. Dry mixed-conifer forests experienced relatively short fire intervals (mean 21 years) and low fire severity, and regeneration of the main conifer species was largely dependent on open conditions sustained over successive fires. Moist mixed-conifer forests experienced longer fire intervals (mean 32 years) and a broader range of severities, and fire-caused canopy openings were important for initiating pulses of tree recruitment. Most (83%) aspen stands included two or more post-fire cohorts. The methods presented here can be adapted to other mixed-severity systems to better understand their long-term spatial and temporal dynamics and develop restoration priorities.

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TL;DR: In this paper, the current and future status of forests in Ukraine and Belarus that were contaminated after the nuclear disaster in 1986 using several models, together with remote-sensing data and observations, studied how climate change in these forests may affect fire regimes.
Abstract: In this paper, we analyze the current and future status of forests in Ukraine and Belarus that were contaminated after the nuclear disaster in 1986 Using several models, together with remote-sensing data and observations, we studied how climate change in these forests may affect fire regimes We investigated the possibility of 137Cs displacement over Europe by studying previous fire events, and examined three fire scenarios that depended on different emission altitudes of 137Cs, assuming that 10% of the forests were affected by fires Field measurements and modeling simulations confirmed that numerous radioactive contaminants are still present at these sites in extremely large quantities Forests in Eastern Europe are characterized by large, highly fire-prone patches that are conducive to the development of extreme crown fires Since 1986, there has been a positive correlation between extreme fire events and drought in the two contaminated regions Litter carbon storage in the area has doubled since 1986

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TL;DR: It is suggested that hierarchical Bayesian statistical approaches offer important advantages over frequentist methods for building and interpreting IPMs, especially given the hierarchical nature of most demographic studies.
Abstract: Integral projection models (IPMs) are a powerful and popular approach to modeling population dynamics. Generalized linear models form the statistical backbone of an IPM. These models are typically fit using a frequentist approach. We suggest that hierarchical Bayesian statistical approaches offer important advantages over frequentist methods for building and interpreting IPMs, especially given the hierarchical nature of most demographic studies. Using a stochastic IPM for a desert cactus based on a 10-year study as a worked example, we highlight the application of a Bayesian approach for translating uncertainty in the vital rates (e.g., growth, survival, fertility) to uncertainty in population-level quantities derived from them (e.g., population growth rate). The best-fit demographic model, which would have been difficult to fit under a frequentist framework, allowed for spatial and temporal variation in vital rates and correlated responses to temporal variation across vital rates. The corresponding poste...

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TL;DR: In this article, the authors compare a suite of spatiotemporal hierarchical models for animal count data that permit animal density to vary over space and time, including formulations motivated by resource selection and allowing for closed populations.
Abstract: Ecologists often fit models to survey data to estimate and explain variation in animal abundance. Such models typically require that animal density remains constant across the landscape where sampling is being conducted, a potentially problematic assumption for animals inhabiting dynamic landscapes or otherwise exhibiting considerable spatiotemporal variation in density. We review several concepts from the burgeoning literature on spatiotemporal statistical models, including the nature of the temporal structure (i.e., descriptive or dynamical) and strategies for dimension reduction to promote computational tractability. We also review several features as they specifically relate to abundance estimation, including boundary conditions, population closure, choice of link function, and extrapolation of predicted relationships to unsampled areas. We then compare a suite of novel and existing spatiotemporal hierarchical models for animal count data that permit animal density to vary over space and time, including formulations motivated by resource selection and allowing for closed populations. We gauge the relative performance (bias, precision, computational demands) of alternative spatiotemporal models when confronted with simulated and real data sets from dynamic animal populations. For the latter, we analyze spotted seal (Phoca largha) counts from an aerial survey of the Bering Sea where the quantity and quality of suitable habitat (sea ice) changed dramatically while surveys were being conducted. Simulation analyses suggested that multiple types of spatiotemporal models provide reasonable inference (low positive bias, high precision) about animal abundance, but have potential for overestimating precision. Analysis of spotted seal data indicated that several model formulations, including those based on a log-Gaussian Cox process, had a tendency to overestimate abundance. By contrast, a model that included a population closure assumption and a scale prior on total abundance produced estimates that largely conformed to our a priori expectation. Although care must be taken to tailor models to match the study population and survey data available, we argue that hierarchical spatiotemporal statistical models represent a powerful way forward for estimating abundance and explaining variation in the distribution of dynamical populations.


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TL;DR: Individual-based spatially explicit simulation models of two mixed conifer–angiosperm forests, growing on soils of contrasting phosphorus (P) availability, are constructed to investigate how browsing by invasive red deer and granivory by invasive rodents might alter forest dynamics.
Abstract: Understanding the long-term impacts of invasive mammalian browsers and granivores in mixed forests is difficult due to the many processes potentially affecting the demography of long-lived trees. We constructed individual-based spatially explicit simulation models of two mixed conifer–angiosperm forests, growing on soils of contrasting phosphorus (P) availability, to investigate how browsing by invasive red deer (Cervus elaphus scoticus) and granivory by invasive rodents (primarily house mouse Mus musculus) might alter forest dynamics. Models were parameterized with field data. Seedling growth and survival rates were estimated inside and outside deer exclosures. Seed predation rates were estimated at high and low rodent densities in mast and non-mast seeding years. For the alluvial terrace forest, which grew on P-rich soil, our model contained 15 tree species dominated by angiosperms; our model of the P-poor marine terrace forest contained seven species dominated by conifers. The two forest models were us...

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TL;DR: In this paper, the Bormann-Likens hypothesis of a biomass peak followed by a decline to a steady state with zero net growth is tested against alternative hypotheses of asymptotic or increasing trends with positive net growth even at advanced ages.
Abstract: Long-term trends in forest biomass have important implications for carbon sequestration and storage, but chronosequence field studies and computer simulations have produced differing conclusions about whether biomass declines in older stands. In this paper, the Bormann-Likens hypothesis of a biomass peak followed by a decline to a steady state with zero net growth is tested against alternative hypotheses of asymptotic or increasing trends with positive net growth even at advanced ages. Trends in aboveground live-tree biomass and large tree density in northern hardwoods were examined from chronosequences and 30-year permanent plot data from forests spanning a wide range of developmental stages, as well as multi-century simulations using an intensively-tested individual-tree model (CANOPY). Both field data and simulations indicated an average decline in aboveground live-tree biomass and number of large trees in the later stages of old growth under environmental conditions of the recent past. This decline wa...

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TL;DR: In this paper, the authors quantified five biogeochemical processes and an aggregate measure of multifunctionality in species-rich coastal fish communities to test three questions: (1) Do previously predicted biodiversity-ecosystem-function relationships hold across large spatial scales and in highly diverse communities? (2) Can additional covariates of community structure improve these relationships? (3) What is the role of community biomass and functional group diversity in maintaining bio-ochemical processes under various scenarios of species loss across ecosystem types?
Abstract: Small-scale experiments and theory suggest that ecological functions provided by communities become more stable with increased species richness. Whether these patterns manifest at regional spatial scales and within species-rich communities (e.g., coral reefs) is largely unknown. We quantified five biogeochemical processes, and an aggregate measure of multifunctionality, in species-rich coastal fish communities to test three questions: (1) Do previously predicted biodiversity-ecosystem-function relationships hold across large spatial scales and in highly diverse communities? (2) Can additional covariates of community structure improve these relationships? (3) What is the role of community biomass and functional group diversity in maintaining biogeochemical processes under various scenarios of species loss across ecosystem types? These questions were tested across a large regional gradient of coral reef, mangrove and seagrass ecosystems. Statistical models demonstrated that species richness and the mean maximum body size per species strongly predicted biogeochemical processes in all ecosystem types, but functional group diversity was only a weak predictor. Simulating three scenarios of species loss demonstrated that conserving community biomass alone increased the ability for communities to maintain ecosystem processes. Multifunctionality of biogeochemical processes was maintained least in simulations that conserved biomass and community structure, underscoring the relative lack of importance of community structure in maintaining multiple simultaneous ecosystem functions in this system. Findings suggest that conserving community biomass alone may be sufficient to sustain certain biogeochemical processes, but when considering conservation of multiple simultaneous biogeochemical processes, management efforts should focus first on species richness.

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TL;DR: In this article, the authors investigated how and why the scale (local and global spatial extent, spatial grain, duration) and complexity (number of species, factors, treatment combinations) of experiments performed on marine hard substrata (rocky intertidal, RI; coral reef, CR; rocky subtidal, RS; mangrove root, MR) has changed by assessing 311 total experiments published since 1961 in Ecology and Ecological Monographs and since 1967 in Journal of Experimental Marine Biology and Ecology.
Abstract: Manipulative field experiments provide a window into the complexity of nature. Yet there is concern that we lack resolution by conducting experiments on a scale that is too small and short to include the relevant complexity of the study system. We addressed this issue by asking how and why the scale (local and global spatial extent, spatial grain, duration) and complexity (number of species, factors, treatment combinations) of experiments performed on marine hard substrata (rocky intertidal, RI; coral reef, CR; rocky subtidal, RS; mangrove root, MR) has changed by assessing 311 total experiments published since 1961 in Ecology and Ecological Monographs and since 1967 in Journal of Experimental Marine Biology and Ecology. We show that the local spatial extent and all metrics of complexity increased as a positive, log-linear function of time. In contrast, the size of experimental units (spatial grain) decreased with time. Quantile regression analysis revealed that these trends are largely driven by changes ...