Ecological Monographs最新文献

Flower exposure to high temperature reduces the production, viability, and performance of pollen, ovules, and seeds, which in turn impairs individual fecundity and risks the survival of populations. Autonomous floral cooling could alleviate the effects of flower exposure to harmful temperatures, yet investigations on thermal ecology of flowers in hot environments are needed to evaluate the reality, magnitude, and ecological significance of thermoregulatory cooling. This paper reports a study on the thermal ecology of the flower heads (=capitula) of 15 species of summer-blooming Asteraceae, tribe Cardueae, from hot-dry habitats in the southern Iberian Peninsula. Temperature inside (T_in) and outside (T_out) capitula were assessed under natural field conditions using two complementary sampling and measurement procedures, which provided information on the relationships between the two temperatures at the levels of individual capitula (“continuous recording”) and local plant populations (“instantaneous measurements”). Baselines for the T_in–T_out relationship in the absence of physiological activity were obtained by exposing dehydrated capitula to variable ambient temperatures in the field. To assess whether the co-flowering capitula of summer-blooming Asteraceae defined collectively a distinct thermal layer, the vertical distribution of capitula relative to the ground was quantified. Bees visiting capitula were watched and temperature of the air beside the visited capitulum was measured. Results were remarkably similar for all plant species. The capitula experienced high ambient temperatures during long periods, yet their interior was cooler than the air most of the time, with temperature differentials (ΔT = T_in − T_out) often approaching, and sometimes exceeding −10°C. The relationship between T_in and T_out was best described by a composite of one steep and one shallow linear relationship separated by a breakpoint (Ψ, interspecific range = 25–35°C). Capitula were only weakly thermoregulated when T_out < Ψ, but switched to closely thermoregulated cooling when T_out > Ψ. Narrow vertical distributions of capitula above the ground and similar cooling responses by all species resulted in a “refrigerated floral layer” where most bees foraged at T_out > Ψ and presumably visited cooled capitula. Thermoregulatory refrigeration of capitula (“thermal engineering”) can benefit not only plant reproduction by reducing pollen and ovule exposure to high temperatures during the summer but also the populations of bee pollinators and other floricolous insects.

The rising introduction of invasive species through trade networks threatens biodiversity and ecosystem services. Yet, we have a limited understanding of how transportation networks determine spatiotemporal patterns of range expansion. This knowledge gap may stem from two reasons. First, current analytical models fail to integrate the invader's life-history dynamics with heterogeneity in human-mediated dispersal patterns. Second, classical statistical methods often fail to provide reliable estimates of model parameters, such as the time and place of species introduction and life-history characteristics, due to spatial biases in the presence-only records and lack of informative demographic data. To address these gaps, we first formulate an age-structured metapopulation model that uses a probability matrix to emulate human-mediated dispersal patterns. The model reveals that an invader spreads radially along the shortest network path, such that the inter-patch network distances decrease with increasing traffic volume and reproductive value of hitchhikers. Next, we propose a hierarchical Bayesian statistical method to estimate model parameters using presence-only data and prior demographic knowledge. To show the utility of the statistical approach, we analyze zebra mussel (Dreissena polymorpha) expansion in North America through the inland commercial shipping network. Our analysis suggests that zebra mussels might have been introduced before 1981, indicating a lag of 5 years between the time of introduction and first detection in late 1986. Furthermore, using our statistical model, we estimated a one in three chance that they were introduced near Kingsville (Ontario, Canada), where they were first reported. We also find that survival, fecundity, and dispersal during early life (1–2 years) play a critical role in determining the expansion success of these mollusks. These results underscore the importance of fusing prior scientific knowledge with observation and demographic processes in a Bayesian framework for conceptual and practical understanding of how invasive species spread by human agency.

Batrachochytrium dendrobatidis (Bd) is a globally distributed fungal pathogen of amphibians that has contributed to one of the largest disease-related biodiversity losses in wildlife. Bd is regularly viewed through the lens of a global wildlife epizootic because the spread of highly virulent genetic lineages has resulted in well-documented declines and extinctions of multiple amphibian species. However, the current state of Bd occurrence, host range, host impacts, and ecological drivers remains poorly understood outside of the most negatively affected amphibian species and regions. Our objective was to describe the macroecology of Bd occurrence and infection intensity on caudates (salamanders) across the United States and to compare these patterns with better-studied anurans (frogs and toads). We collected swabs from 11,183 amphibians at 609 sites from 54 species across the United States from 2015 to 2017. We analyzed the prevalence and intensity of Bd infection jointly using a Bayesian hurdle model with covariates of site-level temperature and precipitation, as well as individual characteristics and species identification. Bd was distributed widely across sites and species sampled across the spatial extent of the conterminous United States. We found that Bd prevalence and intensity were most strongly influenced by temperature in the month preceding sampling and by differences among taxon groups. We estimated that temperature had a strong and nonlinear influence on both Bd prevalence and intensity with peak infection at intermediate temperatures and lower infection at low and high temperatures. We found Caudate hosts tended to have higher prevalence than Anuran hosts and Anuran hosts tended to have higher intensity at optimal temperatures for Bd infection. Our findings suggest that Bd has an amphibian-wide host range, temperature gradients exert a strong influence on Bd, and enzootic transmission likely encompasses a much larger spatial and species distribution than previously recognized across North America.

The strength of biodiversity–ecosystem functioning (BEF) relationships varies within and across studies, depending on the investigated ecosystem function and diversity facet (e.g., species richness or functional composition), limiting our ability to translate BEF results into recommendations for management and conservation. The variability in BEF relationships is particularly high when considering complex multitrophic communities and can be explained by food web contexts. Here we examine how different plant diversity facets affect biomass stocks and energy flows of each trophic group depending on their position in the trophic network. We used coupled aboveground–belowground multitrophic networks of energy dynamics, assembled across the experimental gradients of grassland plant species richness, functional diversity, and presence of plant functional groups. We compared the strengths of these diversity effects between trophic groups, trophic levels, aboveground versus belowground subnetworks, and types of ecosystem functions. Plant species richness, functional trait diversity, and the presence of legumes and grasses were influential drivers of ecosystem energetics. The effects of plant species richness across the food web often operated through mechanisms of plant functional-trait diversity. The effects of plant species richness attenuated across trophic levels. Legume presence strengthened the top-down control (predation) of primary consumers. We found an overall mismatch in the strength of diversity effects on flows versus stocks. Some trophic groups showed even contrasting direction in responses of their stocks and flows to plant diversity. This indicates that plant diversity constrains consumer functioning by means other than only altered consumer biomass. Responses of flows and stocks to plant diversity differed between trophic groups, and aboveground versus belowground parts. Individual stocks and energy flows were responsive to different biodiversity facets, highlighting the importance of the explicit consideration of individual functions and diversity facets for a comprehensive multitrophic understanding. For example, legume presence increased aboveground processes but reduced plant carbon uptake and belowground plant production. Plant communities containing legumes lost more biomass to herbivores, had faster decomposition, and channeled less energy to soil detritus. An important implication of these results is that targeted grassland management would profit from focusing on specific plant diversity facets depending on the ecosystem function or service of interest.

Deadwood stores about 8% of global carbon stock, and its decomposition is a key factor in forest ecosystems. Deadwood-associated (saproxylic) organisms constitute a food web that sustains a substantial part of biodiversity globally. After fungi, saproxylic beetles are the most prominent agents of structural deadwood decomposition in forests. They are often classified according to their presumed link to the deadwood decomposition gradient, generally as feeding on fresh wood, decayed wood, fungi, or predators. These classifications are, however, based on ecomorphological characters (e.g., trophic morphology, habitat use) while information on their diet is globally limited. Carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios represent potential useful tracers to improve knowledge on the trophic ecology of this model group and the whole decomposition food web. We performed stable isotope analysis on 121 beetle species (530 samples) from a mixed-deciduous forest in Central Europe in order to (1) characterize drivers of saproxylic beetles' isotopic variability with respect to potential food sources along the wood decomposition gradient and in relation to the potentially key intrinsic factors such as phylogeny and body size and (2) to assess how isotope information matches with two trophic guild classifications based on ecomorphological characters which are commonly used in ecological studies. The analysis revealed a clear pattern of δ¹³C increase and simultaneous C:N ratio decrease across potential food sources along the gradient from fresh to decayed deadwood and fungi. Beetle phylogeny and body size explained a significant part of their isotope variability, with values of δ¹³C being lower in smaller species. After filtering out these effects, the δ¹³C values reflected the position of beetle species on the decomposition gradient only loosely. Fungi-feeding guilds had higher δ¹³C values than the guilds dependent on fresher deadwood, but otherwise the guilds were indistinguishable. Deadwood consumers did not differ from predators. The isotopic niches of different feeding guilds largely overlapped, and the large observed variation suggests that not only fungi feeders but species from most guilds may depend considerably on fungi and that mixed trophic strategies may be more common in the decomposition food web than currently acknowledged.

Freshwater snails play a key role in the transmission of schistosomiasis, a tropical parasitic disease affecting over 150 million people. Adaptation of these snails to local climatic conditions is a critical factor in determining how climate change and other environmental factors influence disease transmission dynamics, yet this potential adaptation has remained unexplored. Bulinus truncatus is the schistosome intermediate host snail with the widest geographic distribution and is therefore an important factor determining the maximum range of urogenital schistosomiasis. In this study, we assessed the local adaptation capacity of B. truncatus to temperature through an integrative approach encompassing phenotypic, ecophysiological, and genomic data. Ten snail populations from diverse thermal environments were collected in three countries, with eight populations reared in a common garden. The F2 generation (N = 2304) was exposed to eight chronic temperature treatments (±36 snails/population/temperature treatment) and various life history traits were recorded for over 14 weeks. Subsequently, ecophysiological analyses were conducted on the 10 last surviving snails per population. Genotyping the parental generation collected in the field using a genotyping-by-sequencing (GBS) approach, revealed 12,875 single-nucleotide polymorphisms (SNPs), of which 4.91% were potentially under selection. We observed a significant association between outlier SNPs, temperature, and precipitation. Thermal adaptations in life history traits were evident, with lower survival rates at high temperatures of warm-origin snails compensated for by higher reproduction rates. Cold-origin snails, on the other hand, exhibited higher growth rates adapted to a shorter growing season. Ecophysiological adaptations included elevated sugar and hemoglobin contents in cold-adapted snails. In contrast, warm-adapted snails displayed not only increased protein levels but also more oxidative damage. Furthermore, heightened phenoloxidase levels indicated a more robust immune response in snails from parasite-rich regions. These morphological and physiological differences provide convincing evidence for a genetic basis of local adaptation. This in turn holds profound implications for the snail's response to climate change, future schistosomiasis risk, and the effectiveness of schistosomiasis control measures.

Quantifying terrestrial carbon (C) sequestration potential is crucial for climate change mitigation and achieving C neutrality. Ecosystem manipulative experiments (EMEs) provide valuable in situ assessments of terrestrial C dynamics under global change. Although EMEs have expanded rapidly in China, their current state and role in elucidating spatial drivers of the country's terrestrial C sink and responses to major global change factors remain underexplored. This study systematically reviewed 1140 publications on Chinese EMEs, compiling a dataset of net primary productivity (NPP) and net ecosystem productivity (NEP). We identified 558 EMEs in China since 1991, marked by two phases: (1) a preliminary stage (1991–2004) and (2) exponential growth (2005–present). Most EMEs focused on grasslands, with limited emphasis on CO₂ enrichment and studies in Northwest China. Our findings revealed that China's terrestrial ecosystems serve as a significant C sink (positive NEP), with sink strength positively associated with temperature, soil clay, silt, and nitrogen (N) contents, and negatively with soil sand content and bulk density. Optimal conditions for NPP and NEP were observed at precipitation levels of 850–1176 mm and soil pH between 6.5 and 7.0. Elevated CO₂ levels stimulated NPP and NEP when combined with N addition, particularly organic N, and effects varied with temperature and soil texture (clay, silt, and sand contents). Warming impacts differed by ecosystem and facility type, reducing NPP in wetlands and NEP in open-top chambers. Combined warming with water or N addition generally increased NPP and NEP, while coupling it with reduced precipitation caused declines. Warming above 1.5°C often had adverse impacts. Both NPP and NEP responded nonlinearly to precipitation, exhibiting negative asymmetry in their responses to anomalies. Nitrogen addition consistently stimulated NPP and NEP, with responses influenced by application rates, frequency, duration, and soil texture and pH. Additive effects of combined global change factors on NPP and NEP were common. To improve our understanding of terrestrial C feedbacks to anthropogenic changes, future research should focus on long-term, multifactor studies in mature forests and wetlands, aiding in the pursuit of net-zero targets.

Pollinator-mediated and pollinator-independent interactions both affect plant reproductive success but are often studied independently. Evaluating the separate and cumulative effect of both types of interactions is necessary to understand population dynamics and species coexistence. Here, we ask how interactions during growth and flowering contribute to pollinator-mediated and pollinator-independent density dependence in components of reproduction and total fecundity in communities of Clarkia species. Using experimental plots embedded in natural communities of forbs and grasses, we examine the response of flower number, ovule number per flower, seed set (% of ovules in a fruit that are filled seed), and total fecundity (total seed number per plant) of focal plants of four Clarkia species to varying densities of background Clarkia, forbs, and grasses, with (control) or without supplemental pollination of focal flowers. A comparison of seed set and total fecundity between control and pollen-supplemented flowers provided an estimate of pollen limitation to reproduction, which was largely pollinator mediated in this study. Forbs and grasses exerted a density-dependent, pollinator-independent competitive effect on all reproductive components and on total fecundity. By contrast, interactions between focal and background Clarkia were entirely density-independent, pollinator-mediated, and affected only seed set. Pollinator-mediated effects on seed set between pairs of focal and background Clarkia species were largely competitive, and in line with the known pollination biology of Clarkia species. Our results point to the importance of evaluating pollinator-mediated interactions in the context of natural communities, and that pollinator-mediated interactions between Clarkia species, while strong, are not likely to affect population dynamics at the scale of the small local neighborhood but may do so at larger spatial and/or temporal scales.

Spatial variations in food availability may influence life-history traits of wildlife species, particularly in capital-breeding species that store energy when food is widely available and catabolize it during energy-intensive reproductive periods. The reproductive success of capital breeders is thus highly dependent on the accumulation of fat reserves. Reproductive success may also improve with access to alternative food resources provided by environments with strong human footprint and anthropogenic disturbances, but these environments may also increase mortality risks of wildlife. We performed a systematic review to extract reproduction and survival traits reported in studies on the American black bear (Ursus americanus), a capital breeder. Based on 94 studies widely distributed across North America, we conducted meta-regression analyses to assess whether interpopulation variation in age at primiparity, litter size of cubs, annual cub survival, and annual survival of adult females were associated with environmental conditions, that is, habitat quality, habitat productivity, and anthropogenic disturbances. We found that mean age at primiparity decreased from around 5 to 4 years old in areas with the highest habitat quality and productivity as well as the highest human population densities compared with those with poor habitat quality and productivity and low human population densities. Mean litter size increased by approximately 13% (from 2 to 2.25 cubs per litter) in areas with the highest compared with the lowest proportion of deciduous forest, while cub survival increased by about 13% (from 60% to 73%) in areas with the highest compared with the lowest coverage of agricultural crops. Adult female survival decreased from 92% to 85% in areas where hunting was allowed. These results provide new insights into the factors associated with variations in reproductive success and survival across populations of a widely distributed species, demonstrating the impact of both natural and anthropogenic factors. Our study highlights the necessity of considering the ongoing changes in the distribution and growth of potential food resources, as well as the growing encroachment of humans into wildlife habitats, when planning management and conservation actions at the scale of a species distribution range.

The behavior and abundance of sympatric predators can be affected by a complex dominance hierarchy. The strength of antagonistic interactions in predator communities is difficult to study and remains poorly understood for many predator assemblages. Predators directly and indirectly influence the broader ecosystem, so identifying the relative importance of competition, prey, and habitat in shaping predator interactions has broad conservation and management implications. We investigated space use among five predator species (black bear [Ursus americanus], bobcat [Lynx rufus], coyote [Canis latrans], mountain lion [Puma concolor], and gray wolf [Canis lupus]) across three temporal scales in northern Idaho, USA. We used camera trap data to test whether potentially subordinate predators spatially avoided dominant predators and how prey availability influenced those relationships. We found few instances of subordinate predators spatially avoiding dominant predators and only at the finest temporal scale of our analyses. Instead, habitat features generally influenced predator space use patterns at coarser scales whereas prey and competitor presence influenced space use patterns at finer scales. Co-occurrence was positively associated between coyotes and bobcats at coarser timescales and between mesopredators and apex predators at finer timescales. Bobcats and mountain lions temporarily delayed the use of sites recently visited by coyotes and black bears, respectively. And all predator species used sites sooner following the detection of a competitor in areas with higher relative abundances of prey (primarily white-tailed deer [Odocoileus virginianus]). Our results suggest attraction to shared habitats and prey resources influenced space use in the predator community more than avoidance of competitors. We propose that the effects of interspecific interactions on predator distributions were most evident for mesopredators because their trophic position requires balancing risks and rewards associated with prey, apex predators, and other mesopredators. In addition, relatively high densities of a common prey source likely facilitated the spatial coexistence in this predator community. Our study demonstrates the value of simultaneously assessing multiple interspecific interactions across different spatiotemporal scales to discern relationships within the predator guild.