Ecological Monographs最新文献

Plants produce a great number of phytochemicals serving a variety of different functions. Recently, the chemodiversity of these compounds (i.e., the diversity of compounds produced by a plant) has been suggested to be an important aspect of the plant phenotype that may shape interactions between plants, their environment, and other organisms. However, we lack an agreement on how to quantify chemodiversity, which complicates conclusions about the functional importance of it. Here, we discuss how chemodiversity (deconstructed into components of richness, evenness and disparity) may relate to different ecologically relevant aspects of the phenotype. Then, we systematically review the literature on chemodiversity to examine methodological practices, explore patterns of variability in diversity across different levels of biological organization, and investigate the functional role of this diversity in interactions between plants and other organisms. Overall, the reviewed literature suggests that high chemodiversity is often beneficial for plants, although a heterogeneity of methodological approaches partly limits what general conclusions can be drawn. Importantly, to support future research on this topic, we provide a framework with a decision tree facilitating choices on which measures of chemodiversity are best used in different contexts and outline key questions and avenues for future research. A more thorough understanding of chemodiversity will provide insights into its evolution and functional role in ecological interactions between plants and their environment.

Seminal ecological theories, island biogeography and the single large or several small (SLOSS) reserve debate, examine whether large contiguous habitats conserve biodiversity better than multiple smaller patches. Today, delineating the ecological effects of habitat area versus configuration in a fragmentation context remains difficult, and often confounds efforts to understand proximate and ultimate drivers of community change in response to habitat alteration. We examined how the major components of fragmentation, habitat division versus area loss, independently influence faunal communities using landscapes constructed from artificial seagrass at scales relevant for juvenile estuarine nekton. We deployed 25 unique, 234-m² landscapes designed along orthogonal axes: habitat percent cover (i.e., area) and fragmentation per se (i.e., patchiness) to examine their effects on faunal density, community composition, and probability of bait-assay consumption. Faunal sampling occurred in both artificial seagrass and interspaced sandflat matrix. We also examined whether larval-settler density drove faunal density patterns across landscapes. Further, we assessed the relative importance of landscape-scale parameters versus fine-scale complexity–canopy height and epiphyte biomass–in determining faunal densities. We most consistently observed increasing epibenthic fish and macroinvertebrate density with increasing seagrass percent cover. Fragmentation per se only negatively affected epibenthic faunal density within the matrix at low seagrass coverage. Bait consumption increased with seagrass cover, suggesting larger habitats are relative foraging hotspots. Alternatively, benthopelagic fish density was unaffected by habitat parameters, reflecting lower seagrass reliance, or increased matrix tolerance. Community compositions did not vary across landscapes, suggesting that abundant species used landscapes indiscriminately. Finally, the relative importance of habitat parameters shifted across faunal guilds and life stages. Landscape percent cover most affected epibenthic faunal density, but not benthopelagic fish density, and neither pattern was related to settler density. Further, only fine-scale complexity influenced settler densities. Collectively, our results indicate habitat area is a primary, positive driver of faunal densities and generalist consumption, and therefore should be prioritized in seagrass conservation. However, sampling across spatial scales and habitat types revealed nuances in habitat use patterns among faunal guilds and life stages that were not solely area-dependent, illustrating that a variety of landscape configurations support essential nursery functions.

Changes in host species richness can alter infection risk and disease levels in multi-host communities. I review theoretical predictions for direct and environmental transmission pathogens about the effects of host additions (or removals) on three commonly used disease metrics: the pathogen community reproduction number $��\left(R_0\right)�$ and infection prevalence and infected density in a focal host. To extend this prior work and explain why predictions differ between metrics, I analyze Susceptible Infected-Recovered-type models of an environmentally transmitted pathogen and multiple host species that compete for resources. Using local sensitivity analysis, I show how trait-mediated and density-mediated indirect effects drive each metric's response to variation in an added host's ability to transmit a pathogen, the added host's density, and the pathogen transmission mechanism. For each disease metric, the responses are typically predicted by the added host's ability to transmit the pathogen when interspecific competition is weak whereas the responses can be altered by shifts in host densities when interspecific competition is strong. In addition, the three metrics often respond in the same direction. However, the metrics can respond in different directions for three reasons: (1) differences between the ability of exposed individuals to transmit the pathogen over the length of time the individuals are infected (i.e., host competence) and a host population's instantaneous net rate of production of infectious propagules; (2) strong density-mediated feedbacks driven by disease-induced mortality; and (3) host additions or removals cause large changes in focal host density via competition or disease-induced mortality. This study extends and unifies prior theoretical studies, and helps identify the rules governing the context-dependent relationships between host species richness and the three metrics of disease.

Global warming has been shifting climatic envelopes of many tree species to higher latitudes and elevations across the globe; however, unsuitable soil biota may inhibit tree migrations into these areas of suitable climate. Specifically, the role of mycorrhizal fungi in facilitating tree seedling establishment beyond natural species range limits has not been fully explored within forest ecosystems. We used three experiments to isolate and quantify the effects of mycorrhizal colonization and common mycorrhizal networks (CMN) on tree seedling survival and growth across (within and beyond) the elevational ranges of two dominant tree species in northeastern North America, which were associated with either arbuscular mycorrhiza (AMF, Acer saccharum) or ectomycorrhiza (EMF, Fagus grandifolia). In order to quantify the influence of mycorrhiza on seedling establishment independent of soil chemistry and climate, we grew seedlings in soils from within and beyond our study species ranges in a greenhouse experiment (GE) as well as in the field using a soil translocation experiment (STE) and another field experiment manipulating seedling connections to potential CMNs (CMNE). Root length colonized, seedling survival and growth, foliar nutrients, and the presence of potential root pathogens were examined as metrics influencing plant performance across species' ranges. Mycorrhizal inoculum from within species ranges, but not from outside, increased seedling survival and growth in a greenhouse setting; however, only seedling survival, and not growth, was significantly improved in field studies. Sustained potential connectivity to AMF networks increased seedling survival across the entire elevational range of A. saccharum. Although seedlings disconnected from a potential CMN did not suffer decreased foliar nutrient levels compared with connected seedlings, disconnected AM seedlings, but not EM seedlings, had significantly higher aluminum concentrations and more potential pathogens present. Our results indicate that mycorrhizal fungi may facilitate tree seedling establishment beyond species range boundaries in this forested ecosystem and that the magnitude of this effect is modulated by the dominant mycorrhizal type present (i.e., AM vs. EM). Thus, despite changing climate conditions beyond species ranges, a lack of suitable mutualists can still limit successful seedling establishment and stall adaptive climate-induced shifts in tree species distributions.

Alternative perspectives on the maintenance of biodiversity and the assembly of ecological communities suggest that both processes cannot be investigated simultaneously. In this concept and synthesis, we challenge this view by presenting major theoretical advances in structural stability and permanence theory. These advances, which provide complementary views, allow studying the short- and long-term dynamics of ecological communities as changes in species richness, composition, and abundance. Here, the global attractor, technically named informational structure (IS), is the central element to construct from information of species' intrinsic growth rates and their strength and sign of interactions. The global attractor has four main properties: (1) It contains all the limits of what is feasible and unfeasible of the dynamical behavior of an ecological system, therefore, (2) it provides a thorough characterization of all combinations of species' richness and composition in which species can coexist (i.e., feasible and stable equilibrium), (3) as well as all connections (paths) of assembly between coexisting communities. Importantly, (4) such topology of coexisting communities and their connections changes when environmental (abiotic and biotic) variation affects the ability of species to grow and interact with others. Overall, these four properties allow switching from a traditional evaluation of species coexistence at equilibrium to a much more realistic nonequilibrium perspective where changes in the structure of the global attractor underlie the transient ecological dynamics. Several fields in ecology can benefit from the study of an IS. For instance, it can serve to evaluate community responses after the end of a perturbation, to design restoration trajectories, to study the consequences of biological invasions on the persistence of native species within communities, or to assess ecosystem health status. We illustrate this latter possibility with empirical observations of 7 years in Mediterranean annual grasslands. We document that extremely wet or dry years generate ISs supporting few coexisting communities and few assembly paths. The remaining communities distinguish winners from losers of ongoing climate change and indicate the limits to future community assembly opportunities. A fully tractable operational framework is readily available to understand and predict the assembly and dynamics of ecological communities in an ever-changing world.

Large mammalian herbivores exert strong top-down control on plants, which in turn influence most ecological processes. Accordingly, the decline, displacement, or extinction of wild large herbivores in African savannas is expected to alter the physical structure of vegetation, the diversity of plant communities, and downstream ecosystem functions. However, herbivore impacts on vegetation comprise both direct and indirect effects and often depend on herbivore body size and plant type. Understanding how herbivores affect savanna vegetation requires disaggregating the effects of different herbivores and the responses of different plants, as well as accounting for both the structural complexity and composition of plant assemblages. We combined high-resolution Light Detection and Ranging (LiDAR) with field measurements from size-selective herbivore exclosures in Kenya to determine how herbivores affect the diversity and physical structure of vegetation, how these impacts vary with body size and plant type, and whether there are predictable associations between plant diversity and structural complexity. Herbivores generally reduced the diversity and abundance of both overstory and understory plants, though the magnitude of these impacts varied substantially as a function of body size and plant type: only megaherbivores (elephants and giraffes) affected tree cover, whereas medium- and small-bodied herbivores had stronger effects on herbaceous diversity and abundance. We also found evidence that herbivores altered the strength and direction of interactions between trees and herbaceous plants, with signatures of facilitation in the presence of herbivores and of competition in their absence. While megaherbivores uniquely affected tree structure, medium- and small-bodied species had stronger (and complementary) effects on metrics of herbaceous vegetation structure. Plant structural responses to herbivore exclusion were species-specific: of five dominant tree species, just three exhibited significant individual morphological variation across exclosure treatments, and the size class of herbivores responsible for these effects varied across species. Irrespective of exclosure treatment, more species-rich plant communities were more structurally complex. We conclude that the diversity and architecture of savanna vegetation depend on consumptive and nonconsumptive plant–herbivore interactions; the roles of herbivore diversity, body size, and plant traits in mediating those interactions; and a positive feedback between plant diversity and structural complexity.

Mountain ecosystems play an important role globally as centers of biodiversity and in providing ecosystem services to lowland populations, but are influenced by multiple global change drivers such as climate change, nitrogen deposition, or altered disturbance regimes. As global change is accelerating and the consequences for humans and nature are intensifying, there is an increasing demand for understanding and predicting the impacts and implications of global change on mountain ecosystems. Manipulation experiments are one of the major tools for testing the causal impacts of global change and establishing a mechanistic understanding of how these changes may transform the global biota from single organisms to entire ecosystems. Over the past three decades, hundreds of such experiments have been conducted in mountainous regions worldwide. To strengthen the experimental evidence for the possible ecological consequences of global change, we systematically reviewed the literature on global change experiments in mountains. We first investigated the spread of manipulation experiments to test the effects of different global change drivers on key biological and ecological processes from the organism to the ecosystem level. We then examined and discussed the balance of evidence regarding the impact of these global change drivers on biological and ecological processes, and outlined the possible consequences for mountain ecosystems. Finally, we identified research gaps and proposed future directions for global change research in mountain environments. Among the major drivers, temperature was manipulated most frequently, generally showing consistent strong impacts between biological and ecosystem processes, functional groups, and habitat types. There is also strong evidence suggesting that changes in water and nutrient availability have a direct impact on the life history and functioning of mountain organisms. Despite these important findings, there are several gaps that require urgent attention. These include experiments testing adult trees in tropical and boreal regions, assessing animal responses and biotic interactions, and investigating aquatic environments and soil systems more extensively. A broader approach that integrates experimental data with field observations and relies on international collaboration through coordinated experiments could help address these gaps and provide a more consistent and robust picture of the impacts of global change on mountain ecosystems.

Parasites can alter the traits or densities of mutualistic partners, potentially destabilizing mutualistic associations that underpin the structure, functioning, and stability of entire ecosystems. Despite the potentially wide-ranging consequences of such disruptions, no studies have directly manipulated parasite prevalence and/or intensity in a mutualistic partner, nor quantified the resulting community-level effects. Here, we investigated the effects of a common trematode parasite (Cercaria opaca) on the strength of a keystone facultative mutualism in western Atlantic salt marshes between the foundational marsh cordgrass, Spartina alterniflora, and the ribbed mussel, Geukensia demissa. Cordgrass increases mussel survivorship and growth through shading, while mussels enhance cordgrass growth by producing nutrient-rich biodeposits. This mutualistic association also creates conditions that enhance biodiversity and ecosystem functioning, and mediates the ability of foundational plants to resist and recover from extreme drought. We used lab and field assays to show how increasing infection with trematode metacercariae negatively influenced mussel biodeposit production, as well as the strength of mussel shells and byssal attachments. By conducting a field manipulation using experimentally infected mussels, we demonstrated that the mutualistic benefits of mussels to cordgrass growth decreased with increasing trematode infection intensity—a pattern likely generated by reduced mussel biodeposition and enhanced mortality. Additionally, increasing parasite loads in mussels led to predictable decreases in the abundances of benthic invertebrates, as well as in key ecosystem characteristics and process rates (i.e., redox potential and sediment accretion). Finally, a survey of five North Carolina salt marshes demonstrated that infection with C. opaca was most common in mussels in areas experiencing cordgrass die-off due to drought, and that infection intensity decreased with distance from die-off areas. Because the mussel–cordgrass mutualism underpins marsh ecosystem resilience to drought-associated die-off, our results suggest that parasitism may depress recovery from these disturbances. Although this is the first experimental demonstration of parasites indirectly altering community structure and functioning by undermining an ecologically influential mutualism, this type of relationship could be common in nature, given that parasites frequently infect influential mutualists.

A core aspiration of the ecological sciences is to determine how systems work, which implies the challenge of developing a causal understanding. Causal inference has long been approached from a statistical perspective, which can be limited and restrictive for a variety of reasons. Ecologists and other natural scientists have historically pursued mechanistic knowledge as an alternative approach to causal understanding, though without explicit reference to the requirements of causal statistics. In this paper, I describe the premises of an expanded paradigm for causal studies, the Integrative Causal Investigation Paradigm, that subsumes causal statistics and mechanistic investigation into a multi-evidence approach. This paradigm is distinct from the one articulated by causal statistics in that it (1) focuses its attention on the long-term goal of building causal knowledge across multiple studies and (2) recognizes the essential role of mechanistic investigations in establishing a causal understanding. The Integrative Paradigm, consequentially, proposes that there are multiple methodological routes to building causal knowledge and thus represents a pluralistic perspective. This paper begins by describing the crux of the problem faced by causal statistics. To understand this problem, it should be recognized that the word causal has multiple meanings and a variety of evidential standards. An expanded vocabulary is developed so as to reduce ambiguities and clarify critical issues. I further show by example that there is an important ingredient typically omitted from consideration in causal statistics, which is the known information related to the mechanisms underlying relationships being evaluated. To address this issue, I describe a procedure, Causal Knowledge Analysis, that involves an evaluation and compilation of existing evidence indicative of causal content and the features of mechanisms. Causal Knowledge Analysis is applied to three example situations to illustrate the process and its potential for contributing to the development of causal knowledge. The implications of adopting the proposed paradigm and associated procedures are discussed and include the potential for advancing ecology, the potential for clarifying causal methodology, and the potential for contributing to predictive forecasting.

Community-wide assembly of plant–pollinator systems depends on an intricate combination of biotic and abiotic factors, including heterogeneity among pollinators in thermal biology and responses to abiotic factors. Studies on the thermal biology of pollinators have mostly considered only one or a few species of plants or pollinators at a time, and the possible driving role of the diversity in thermal biology of pollinator asemblages at the plant community level remains largely unexplored. More specifically, it is unknown whether diversity in the thermal biology of bees, a major pollinator group worldwide, contributes to the assembly and maintenance of diverse bee communities; broadens the spectrum of possibilities available to bee-pollinated plants; facilitates interspecific partitioning of ecological gradients across habitats, seasons, and time of day; and/or enhance plant pollination success through complementarity effects. The objectives of this study were to assess the diversity in thermal biology of the bee assemblage that pollinates plants in a Mediterranean montane area, evaluate its taxonomic and phylogenetic underpinnings, and elucidate whether there existed seasonal, daily, between-habitat, or floral visitation correlates of bee thermal biology which could contribute to partition ecological gradients among plant and bee species. Thermal biology parameters were obtained in the laboratory (K, intrinsic warming constant) and the field (thoracic and ambient temperature at foraging site, T_th and T_air) on individual bees of a diverse sample (N = 204 bee species) comprising most bee pollinators of the regional plant community. Species-specific thermal biology parameters were combined with quantitative field data on bee pollinators and flower visitation for the regional community of entomophilous plants (N = 292 plant species). Results revealed that the regional bee assemblage harbored considerable diversity in thermal biology features; that such diversity was mostly taxonomically, phylogenetically, and body-size structured; and that the broad interspecific heterogeneity in thermal biology represented in the bee community as a whole eventually translated into daily, seasonal, among-habitat, and flower visitation patterns at the plant community level. This lends support to the hypothesis that broad diversity in thermal biology of bees can enhance opportunities for bee coexistence, spatiotemporal partitioning of floral resources, and plant pollination success.