Ecological Monographs最新文献

Variance partitioning is a common tool for statistical analysis and interpretation in both observational and experimental studies in ecology. Its popularity has led to a proliferation of methods with sometimes confusing or contradicting interpretations. Here, we present variance partitioning in a model-based Bayesian framework as a general tool for summarizing and interpreting regression-like models to produce additional insight on ecological studies compared with what traditional parameter inference of these models on its own can reveal. For example, we propose predictive variance partitioning as a tool to extend sample-based analyses to analyses of whole populations or predictive scenarios. We also extend variance partitioning to encompass partitioning of variance within and between ecologically relevant subgroups of the observations, or the whole population of interest, to provide information on how the relative roles of processes underlying the study system may vary depending on the environmental or ecological context. We discuss the role of correlated covariates and random effects and highlight uncertainty quantification in variance partitioning. To showcase the utility of our approach, we present a case study comprising a simple occupancy model for a metapopulation of the Glanville fritillary butterfly. As a result, we demonstrate model-based variance partitioning as a general and rigorous statistical tool to gain more insight from ecological data.

Identifying the specific environmental features and associated density-dependent processes that limit population growth is central to both ecology and conservation. Comparative assessments of sympatric species allow for inference about how ecologically similar species differentially respond to their shared environment, which can be used to inform community-level conservation strategies. Comparative assessments can nevertheless be complicated by interactions and feedback loops among the species in question. We developed an integrated population model based on 61 years of ecological data describing the demographic histories of Canvasbacks (Aythya valisineria) and Redheads (Aythya americana), two species of migratory diving ducks that utilize similar breeding habitats and affect each other's demography through interspecific nest parasitism. We combined this model with a transient life table response experiment to determine the extent that demographic rates, and their contributions to population growth, were similar between these two species. We found that demographic rates and, to a lesser extent, their contributions to population growth covaried between Canvasbacks and Redheads, but the trajectories of population abundances widely diverged between the two species during the end of the twentieth century due to inherent differences between the species life histories and sensitivities to both environmental variation and harvest pressure. We found that annual survival of both species increased during years of restrictive harvest regulations; however, recent harvest pressure on female Canvasbacks may be contributing to population declines. Despite periodic, and often dramatic, increases in breeding abundance during wet years, the number of breeding Canvasbacks declined by 13% whereas the number of breeding Redheads has increased by 37% since 1961. Reductions in harvest pressure and improvements in submerged aquatic vegetation throughout the wintering grounds have mediated the extent to which populations of both species contracted during dry years in the Prairie Pothole Region. However, continued degradation of breeding habitats through climate-related shifts in wetland hydrology and agricultural conversion of surrounding grassland habitats may have exceeded the capacity for demographic compensation during the nonbreeding season.

Anthropogenic land use change facilitates disease emergence by altering the interface between humans and pathogen reservoirs and is hypothesized to drive pathogen evolution. Here, we show a positive association between land use change and the evolution and dispersal of Zaire ebolavirus (EBOV) and Sudan ebolavirus (SUDV). We update the phylogeographies of EBOV and SUDV, which reveal that the most recent common ancestor of EBOV was circulating around 1960 in the forests of what is now the northwestern Democratic Republic of the Congo, while the most recent common ancestor of SUDV was circulating around 1958 in the southern Sudanese savanna. Both landscapes underwent significant anthropogenic fragmentation between 1940 and 1960, associated with specific colonial “schemes,” which substantially altered local human settlement patterns and the surrounding vegetation to support intensive cash crop agriculture. Since these disturbances, landscape fragmentation was spatiotemporally associated with the divergence and dispersal of new variants of both viruses into new ecoregions of Africa. These variants segregated geographically along ecoregion boundaries, resembling a pattern observable for other bat-borne viruses. The amino acid changes which characterized each variant disproportionately involved glycosylation-sensitive amino acids in the surface glycoprotein domain responsible for immune evasion and attachment to host cells, suggesting adaptation to new hosts amidst changing landscapes. Our results show that land use change not only increases the risk of spillover, but also impacts the evolution of viruses themselves.

All populations are affected by multiple environmental drivers, including climatic drivers such as temperature or precipitation and biotic drivers such as herbivory or mutualisms. The relative response of a population to each driver is critical to prioritizing threat mitigation for conservation and to understanding whether climatic or biotic drivers most strongly affect fitness. However, the importance of different drivers can vary dramatically across species and across populations of the same species. Theory suggests that the response to climatic versus biotic drivers can be affected by both the species' fundamental niche breadth and the latitude of the population at which the response is measured. However, we have few tests of how these two factors affect relative response to drivers separately, let alone tests of how niche breadth and latitude together influence responses. Here, we use a meta-analysis of published studies on population response to climatic and biotic drivers in terrestrial plants, combined with estimates of climatic niche breadth and position within climatic niche derived from herbarium records, to show that species' niche breadth is the primary determinant of response to climatic versus biotic drivers. Namely, we find that response to climatic drivers changes only minimally with increasing niche breadth, while response to biotic drivers increases with niche breadth. We see similar relationships when considering range size instead of niche breadth. Surprisingly, we find no effects of latitude on the relative effect of climatic versus biotic drivers. Our work suggests that populations of species with small and large ranges experience similar extirpation risks due to the negative impacts of climate change. By contrast, populations of species with large (but not small) ranges may be highly susceptible to changes in densities or distributions of interacting species.

Wet tropical forests play an important role in the global carbon (C) cycle, but given current rates of land-use change, nitrogen (N) and phosphorus (P) limitation could reduce productivity in regenerating forests in this biome. Whereas the strong controls of climate and parent material over forest recovery are well known, the influence of vegetation can be difficult to determine. We addressed species-specific differences in plant traits and their relationships to ecosystem properties and processes, relevant to N and P supply to regenerating vegetation in experimental plantations in a single site in lowland wet forest in Costa Rica. Single-tree species were planted in a randomized block design, such that climate, soil (an Oxisol), and land-use history were similar for all species. In years 15–25 of the experiment, we measured traits regarding N and P acquisition and use in four native, broad-leaved, evergreen tree species, including differential effects on soil pH, in conjunction with biomass and soil stocks and fluxes of N and P. Carbon biomass stocks increased significantly with increasing soil pH (p = 0.0184, previously reported) as did biomass P stocks (p = 0.0011). Despite large soil N pools, biomass P stocks were weakly dependent on traits associated with N acquisition and use (N₂ fixation and leaf C:N, p < 0.09). Mass-balance budgets indicated that soil organic matter (SOM) could supply the N and P accumulated in biomass via the process of SOM mineralization. Secondary soil P pools were weakly correlated with biomass C and P stocks (R = 0.47, p = 0.08) and were large enough to have supplied sufficient P in these rapidly growing plantations, suggesting that alteration of soil pH provided a mechanism for liberation of soil P occluded in organo-mineral soil complexes and thus supply P for plant uptake. These results highlight the importance of considering species' effect on soil pH for restoration projects in highly weathered soils. This study demonstrates mechanisms by which individual species can alter P availability, and thus productivity and C cycling in regenerating humid tropical forests, and the importance of including traits into global models of element cycling.

Insect–plant interactions are key determinants of plant and insect fitness, providing important ecosystem services around the world—including the Arctic region. Recently, it has been suggested that climate warming causes rifts between flower and pollinator phenology. To what extent the progression of pollinators matches the availability of flowers in the Arctic season is poorly known. In this study, we aimed to characterize the community phenology of flowers and insects in a rapidly changing Arctic environment from a descriptive and functional perspective. To this end, we inferred changes in resource availability from both a plant and an insect point of view, by connecting resource and consumer species through a metaweb of all the plant–insect interactions ever observed at a site. Specifically, we: (1) characterized species-specific phenology among plants and insects at two High-Arctic sites—Cambridge Bay in Nunavut, Canada, and Zackenberg in Northeast Greenland; (2) quantified competition for flowers using sticky flower mimics; (3) used information on plant–pollinator interactions to quantify supply and demand for pollinator services versus flower resources during the summer; and (4) compared patterns observed within a focal summer at each site to patterns of long-term change at Zackenberg, using a 25-year time series of plant flowering and insect phenology. Within summers, we found evidence of a general mismatch between supply and demand. Over the 25-year time series, the number of weeks per summer when resource supply fell below a standardized threshold increased significantly over time. In addition, variation in resource availability increased significantly over years. We suggest that the number of resource-poor weeks per year is increasing and becoming less predictable in the High Arctic. This will have important implications for plant pollination, pollinator fitness, and the future of the Arctic ecosystem, as both plants and their pollinators are faced with widening resource gaps.

Ecosystems worldwide are experiencing a range of natural and anthropogenic disturbances, many of which are intensifying as global change accelerates. Ecological responses to those disturbances are determined by both the vulnerabilities of species and their interspecific interactions. Understanding how individual species contribute to the (in-)stability of an aggregated community property, or function, is fundamental to ecological management and conservation. Here, we present a framework to identify species contributions to stability based on their absolute and relative responses to disturbances. Using simulations, we show that these two dimensions enable identification of (de-)stabilizing species and reveal that competitive dominance determines the magnitude of both absolute and relative contributions to stability. Applying our framework to empirical data from a multi-site mesocosm experiment showed that species contributions varied among treatments, sites, and seasons. Despite this dependency on both biotic and abiotic contexts, species contributions were generally constrained by their relative dominance in undisturbed conditions. Rare species contributed positively to stability, while dominant species contributed negatively, indicating compensatory dynamics. Our framework offers an important step toward a more mechanistic understanding of ecological stability based on species performance.

Biodiversity is threatened by both climate and land-use change. However, the synergistic impacts of these stressors and the underlying mechanisms remain poorly understood. This study seeks to bridge this knowledge gap by testing two competing hypotheses regarding the concept of the realized thermal niche. The Fixed Niche Breadth hypothesis suggests that a species' thermal niche remains constant despite fluctuations in population density resulting from land-use changes. This hypothesis links habitat loss directly to a reduced availability of suitable climate. Conversely, the Habitat Loss-Allee Effect hypothesis posits that land-use changes narrow the realized thermal niche by lowering population densities, which impairs individual fitness in unfavorable temperatures due to the Allee effect—the positive impact of higher population density on individual fitness. To investigate these hypotheses, we developed an individual-based model that integrates the Allee effect to examine how climate and land-use changes affect population density and the thermal niche in social organisms. We empirically tested our model predictions by studying the distribution and cooperative behavior of burying beetles (Nicrophorus nepalensis), which compete with blowflies for carrion resources, along two elevational gradients in Taiwan. These gradients serve as temperature gradients, one in an intact forest and the other in a human-altered landscape with substantial forest loss. Our results support the model predictions and show that landscape forest loss reduces beetle population densities and disrupts their dispersal dynamics, resulting in smaller cooperative groups. This, in turn, limits the beetles' ability to compete with blowflies in warmer environments, resulting in a contraction of the realized thermal niche. Together, our findings support the Habitat Loss-Allee Effect hypothesis while rejecting the Fixed Niche Breadth hypothesis. By highlighting the effects of habitat loss and fragmentation on both intra- and interspecific social interactions, our study improves understanding of species' vulnerability to the combined threats of climate and land-use change. Ultimately, our results underscore the importance of considering the demographic and behavioral consequences of land-use change when assessing species' vulnerability to climate-land-use synergies.

The removal or addition of a predator in an ecosystem can trigger a trophic cascade, whereby the predator indirectly influences plants and/or abiotic processes via direct effects on its herbivore prey. A trophic cascade can operate through a density-mediated indirect effect (DMIE), where the predator reduces herbivore density via predation, and/or through a trait-mediated indirect effect (TMIE), where the predator induces an herbivore trait response that modifies the herbivore's effect on plants. Manipulative experiments suggest that TMIEs are an equivalent or more important driver of trophic cascades than are DMIEs. Whether this applies generally in nature is uncertain because few studies have directly compared the magnitudes of TMIEs and DMIEs on natural unmanipulated field patterns. A TMIE is often invoked to explain the textbook trophic cascade involving wolves (Canis lupus), elk (Cervus canadensis), and aspen (Populus tremuloides) in northern Yellowstone National Park. This hypothesis posits that wolves indirectly increase recruitment of young aspen into the overstory primarily through reduced elk browsing in response to spatial variation in wolf predation risk rather than through reduced elk population density. To test this hypothesis, we compared the effects of spatiotemporal variation in wolf predation risk and temporal variation in elk population density on unmanipulated patterns of browsing and recruitment of young aspen across 113 aspen stands over a 21-year period (1999–2019) in northern Yellowstone National Park. Only 2 of 10 indices of wolf predation risk had statistically meaningful effects on browsing and recruitment of young aspen, and these effects were 8–28 times weaker than the effect of elk density. To the extent that temporal variation in elk density was attributable to wolf predation, our results suggest that the wolf–elk–aspen trophic cascade was primarily density-mediated rather than trait-mediated. This aligns with the alternative hypothesis that wolves and other actively hunting predators with broad habitat domains cause DMIEs to dominate whenever prey, such as elk, also have a broad habitat domain. For at least this type of predator–prey community, our study suggests that risk-induced trait responses can be abstracted or ignored while still achieving an accurate understanding of trophic cascades.

Spontaneous plant communities have undergone considerable constraints due to human-mediated changes. Understanding how plant communities are shifting in response to land management and climate changes is necessary to predict future ecosystem functioning and improve the resilience of managed ecosystems, such as agroecosystems. Using Mediterranean weed communities as models of managed plant communities in a climate change hotspot, we quantified the extent to which they have shifted from the 1980s to the 2020s in response to climate and management changes in vineyards. The weed communities of the same 40 vineyards in the Montpellier region were surveyed using the same protocol in spring, summer, and autumn, for two years, with a 40-year interval (1978–1979 vs. 2020–2021). In four decades, the annual range of temperatures (i.e., the difference between the warmest month's and the coldest month's mean temperatures) increased by 1.2°C and the summer temperatures by 2°C. Weed management diversified over time with the adoption of mowing that replaced the chemical weeding of interrows. Chemical weeding is now mostly limited to the area under the row. Current weed communities were 41% more abundant, 24% more diverse, and with a less even distribution of abundance across species than the 1980s communities at the vineyard level. Modern communities were composed of more annual species (57% of annual species in the 1980s vs. 80% in the 2020s) with lower community-weighted seed mass and were composed of fewer C4 species. They had higher community-weighted specific leaf area, higher leaf dry matter content, and lower leaf area than the 1980s weed communities. At the community level, the onset of flowering was earlier and the duration of flowering was longer in the 2020s. Climate change induced more stress-tolerant communities in the 2020s while the diversification of weed management practices favored less ruderal communities. This study shows that plant communities are shifting in response to climate change and that land management is a strong lever for action to model more diverse and eventually more desirable weed communities in the future.