Ecography最新文献

Niche partitioning is one of the key mechanisms allowing species coexistence and is especially relevant in species-rich communities. For pollinators, morphology is a major axis in which species differentiate their foraging niche, as it influences the match with flower morphology. Bumblebees Bombus spp. are important pollinators globally, showing their highest diversity of co-occurring species in the Hengduan Mountains region of southwestern China. This community context makes this region an ideal model system to test the importance of niche partitioning for plant–pollinator interactions. In high-elevation, flower-rich meadows, we sampled over four years pollinator–plant interaction networks containing 12 sympatric bumblebee species, varying more than fourfold in tongue length from 4.7 to 21.7 mm. We then assessed the degree of niche partitioning occurring between these bumblebees. We analysed bumblebees' foraging niche widths and overlap, and found that species with longer tongues foraged from a narrower range of flowers. Accordingly, bumblebee species with shorter tongues, who visited a higher diversity of flowering species also showed consistently higher floral overlap with other bumblebee species across years. Despite this morphology-driven niche pattern for species, the interaction network was consistently characterised by a high degree of generalisation across the years. Our results indicate that the co-occurrence of a large number of potentially competing pollinators with high generalisation and niche overlap is possible in flower-rich habitats. We suggest that, in regions of extraordinarily high plant and pollinator diversity and abundance, diverse pollinator communities may also be maintained without strong foraging niche partitioning.

Diel activity rhythms, representing the behavioral pattern of the sleep–wake cycle, may be adjusted by wildlife in response to changes in environmental conditions. An increase in nocturnality is typically recognized as an adaptive strategy to segregate from humans and mitigate heat stress. Numerous studies have investigated spatial patterns and habitat use of large carnivores in human-modified landscapes, but little research has examined their activity rhythms. We compiled Global Positioning System data (2004–2022) for 139 brown bears Ursus arctos from six populations across Europe, representing a human-modified landscape, and the Greater Yellowstone Ecosystem, U.S.A., representing a landscape with limited human impact, which we used to calculate hourly movement rates as an activity proxy. Using a Bayesian approach to model the temporal autocorrelation of activity data, we tested if the extent of nocturnality in brown bears is modulated by intensity of human encroachment, accounting for primary productivity and maximum ambient temperature. All bear populations exhibited a predominantly bimodal, crepuscular pattern of activity, although Yellowstone bears were proportionally more crepuscular and diurnal. Whereas the effect of primary productivity was variable, all European populations became more nocturnal in response to higher human encroachment and reduced diurnal and crepuscular activity at higher summer temperatures, decreasing overall diel activity levels. Yellowstone bears displayed the greatest shift towards nocturnality among all populations in response to increasing human encroachment, and increased nocturnal activity to compensate for lower diurnal and crepuscular activity at higher summer temperatures. Our research indicates that European bears in human-modified landscapes may be reaching a limit in the behavioral plasticity they can manifest in their activity patterns, being already constrained into increased nocturnality. Our findings enhance the understanding of brown bear adaptive capacity to accommodate future changes, such as urbanization and increasing temperatures, to the ecosystems they inhabit.

Terrestrial mammals are found nearly everywhere on Earth. Yet, most taxa are endemic to a single continent; geological, evolutionary, ecological, or physiological filters constrain geographic distributions. Here, we synthesize data on geography, taxonomy, lineage age, dispersal, body size, and diet for > 4000 terrestrial mammals prior to detectable human-mediated biodiversity losses and quantify factors correlated with the likelihood of dispersal between continents. We confirm the uniqueness of being on multiple continents: excluding humans and commensals, only 260 mammals are found on two continents, while six span three or more continents (the red deer, red fox, brown bear, least weasel, and common bent-wing bat), and just a single species – the lion – once had a geographic range that included four continents. Clearly the challenges of colonizing and persisting on multiple continents are severe. No single characteristic enables taxa to be on more than one continent. Rather, a suite of prerequisite conditions under some circumstances lead to distributions spanning multiple continents. The suite of factors facilitating the occupation of two continents, like being volant, are distinct from those that lead to the occupation of three or more, which are primarily faunivores. Other than humans and our commensals, very few species have become truly cosmopolitan over evolutionary time and geographic space.

Phytoplankton communities affect carbon dynamics worldwide, strongly influencing the quality and quantity of organic carbon in coastal ecosystems. Yet, we still know little about the impacts of changing phytoplankton community composition on the potential carbon pathways in estuaries and coasts. Here, we sampled 25 sites along a coastal salinity and nutrient gradient, collecting water for water chemistry and phytoplankton for community composition analyses. For each site, we determined phytoplankton taxonomic diversity and used Bayesian joint species distribution models considering species interactions, taxonomic relatedness and traits to identify key environmental factors driving phytoplankton community composition. Subsequently, we used structural equation modelling to establish direct and indirect links between the identified key environmental factors, taxonomic diversity (richness and evenness) and particulate organic carbon (POC). We found that the phytoplankton distribution along the estuarine gradient was mainly driven by changes in salinity. Increasing salinity (ranging between 0.8–6.4) benefited motile species and reduced the phytoplankton richness, which resulted in a decrease in POC concentration. This indirect effect of salinity on POC was stronger than a direct one, highlighting the mediating role of phytoplankton richness. This emphasizes the importance of diversity regulating coastal biogeochemical processes and suggests that future changes in salinity might shift coastal carbon dynamics due to changes in phytoplankton community composition.

Sampling bias is an inherent problem in widely available biodiversity data, undermining the robustness of correlative species distribution models (SDMs). To some extent, subsampling occurrence data can account for uneven sampling efforts; yet, conventional approaches subsample in geographical space, while subsampling in environmental space remains underexplored. Here, we compared the effectiveness of subsampling methods that correct sampling bias either in geographical space (spatial gridding, spatial distance thinning) or directly in environmental space (environmental gridding), including two novel approaches introduced here: environmental clustering and environmental distance thinning. We hypothesised that environmental subsampling methods would be more effective in improving SDM performance across its three primary uses: explaining, predicting, and projecting. Using a virtual ecologist framework, we assessed SDM performance against four evaluation tests: replicating true species–environment response curves, predicting within the sampling region via internal cross-validation and evaluation against independent data, and projecting outside the sampling region. Our findings demonstrate that environmental subsampling methods, especially environmental clustering and environmental distance thinning, outperformed other methods in yielding robust SDMs in almost all evaluation tests. Interestingly, cross-validation favoured SDMs with no sampling bias correction, highlighting the inability of cross-validation to identify unbiased models. Our findings emphasise a critical conceptual disconnect: SDMs appearing to perform well in predicting species' distributions may not reliably estimate species–environment relationships, nor transfer predictions onto novel environments. Environmental subsampling methods are reliable approaches for all uses, but are particularly suited for explaining species' niches and transferring predictions across space and/or time, such as when anticipating species' responses to climate change or assessing the risk of biological invasions. Conversely, geographic subsampling methods may suffice for predicting species' distributions within their current environmental context, as required in conservation planning. Our study firmly establishes the critical importance of correcting environmental sampling bias, while also providing reliable solutions for supporting biodiversity conservation in an ever-changing world.

Understanding how species' ecological partitioning functions across biomes is fundamental to macroecology and conservation biology. Here, we examine the global distribution of dietary strategies in terrestrial mammals, focusing on how biome specialization modulates trophic diversity and structure at a broad geographical scale. Using species-level data from over 3600 terrestrial mammal species, we constructed a multivariate dietary space and quantified the area, redundancy, dispersion, uniqueness, and turnover of trophic strategies across ten major biomes. Species were classified as biome specialists, moderate generalists, or extreme generalists based on their biome breadth. By analysing biome specialists and generalists separately, we show that biome specialists tend to exhibit more constrained and compositionally distinct dietary niches in less productive biomes, while generalists, particularly moderate generalists, dominate functional space occupancy in all biomes, even the harsher ones such as tundra and taiga. This highlights how environmental constraints and ecological roles shape trophic strategies at a global scale. Notably, extreme generalists tended to exhibit more carnivorous or insectivorous diets, suggesting a strategy based on mobile predation or opportunism rather than a highly diversified omnivory. Despite these general patterns, highly productive biomes supported the greatest diversity of dietary strategies, with higher functional redundancy and niche packing. Nestedness and turnover analyses revealed that biome specialists diets are often subsets of generalists diets, but with significant compositional shifts across biomes. These findings underscore the dual role of biome generalists as both functional stabilizers and potential limiters of ecological diversity, and highlight the vulnerability of specialist species to global change. Our study offers a mechanistic framework for understanding how dietary strategies interact with environmental filtering, and for identifying functional risks in changing ecosystems.

Extreme climatic events are increasing with climate change, producing changes in communities' climatic characterization. So, mismatches (climatic disequilibrium, CD) between climatic conditions inferred from species' requirements (community inferred climate, CIC) and macroclimate may undergo changes with extreme climatic events. Climatic resilience is defined as the ability to maintain or recover community climatic characteristics, regardless of species' identity, after disturbance or stress.

We evaluated the dynamics of plant community climatic characterization in Mediterranean shrublands that experienced a drought event, considering CIC and CD. CIC was calculated by averaging species' climatic niche centroids, weighted by species' relative abundances, in the multivariate environmental space obtained from the climate of the species' geographical occurrence. CD was estimated as Euclidean distance in this space between the observed historic macroclimate and CIC. Climatic resistance was inferred by the distance between pre-drought and drought CIC, climatic resilience by the distance between pre-drought and post-drought CIC, and relative climatic resilience by the same distance weighted by the climatic displacement suffered during the drought. We found a significant reduction in community CD after drought, with CIC becoming more arid, likely due to environmental filtering of those species with wetter distribution. Communities with less pre-drought CD showed higher climatic resistance but pre-drought CD did not explain climatic resilience. Communities with more arid CIC exhibited high climatic resilience regardless of drought impact (high relative climatic resilience), except for certain communities exhibiting highly arid CICs. Communities with less arid CIC showed low relative climatic resilience, as their resilience was associated with high resistance.

The study highlights community impacts by extreme droughts through filtering of species distributed in more humid climates. This produces changes in the CD of communities, whose resilience is determined by CIC, pre-drought CD, and drought impact in terms of CIC change.

Montane species utilize various habitats along elevations to adapt to seasonality, providing an ideal opportunity to study how species respond to shifting environments. This study characterizes seasonal changes in community structure and elevational distributions across multiple taxa in the Central Himalayas. We compared species richness, community co-occurrence network, and composition of mammals and birds across twelve 300-m elevational bands during the warm and cold seasons. We calculated seasonal shifts in the species elevational ranges, assessing how species traits influenced these shifts and testing the most widely accepted hypotheses for seasonal shifts in elevation distribution: the ‘food-limitation hypothesis' and the ‘climatic constraint hypothesis'. Simpler community network structures emerge during cold seasons, with distinct patterns observed across taxa. Mammals and birds exhibit a hump-shaped elevational pattern in species richness, with peak richness shifting to lower elevations in the cold season as high-elevation species moved downslope. Temporal beta diversity from warm to cold seasons were primarily caused by species losses rather than species gains in high- and middle-elevation communities for both taxa. High- and middle-elevation mammals and birds, as well as insectivorous birds, significantly shifted their upper elevational boundaries downslope in the cold season. Innovatively, we analyzed the seasonal distribution shifts of congeneric competing species to understand the interplay between abiotic and biotic factors in driving species' adaptive responses. From warm to cold season, high-elevation genera increased spatial separation while low-elevation genera decreased it, indicating that interspecies relationships adjust to environmental fluctuations and vary across contexts. This study provides empirical evidence of seasonal variations in community structure and species distributions across Himalayan taxa, highlighting how seasonality drives shift in species distributions across elevations and emphasizing the dynamic nature of elevational ranges over time. This variability underscores the need to incorporate elevational range flexibility into climate change research to understand climate-driven distribution shifts.

Globally, forest disturbances caused by herbivorous insects and plant pathogens (i.e. biotic disturbances) have increased since the 1990s, a trend linked in part to climate warming. With increases in biotic disturbance activity, an emerging ecological phenomenon has been documented: biotic disturbance ‘hotspots', or areas where two or more biotic disturbance agents co-occur in space and time. Biotic disturbance hotspots may have important implications for forest resilience, particularly if they erode mechanisms of post-disturbance forest recovery. The factors leading to hotspot occurrence, however, remain poorly understood. We characterized the patterns and drivers of biotic disturbance hotspots occurring from 2000 to 2020 across three broad forested regions in the western United States (US; the Southern Rockies, Middle Rockies, and Cascades). Using Bayesian spatio-temporal models, we evaluated whether hotspots can be predicted from predisposing factors expected to increase forest susceptibility to biotic disturbance (i.e. forest composition, topography, and average climate), as well as inciting factors known to trigger individual bark beetle and pathogen outbreaks (i.e. annual weather). Biotic disturbance hotspots exhibited distinct spatio-temporal patterns and trends within each region. Forest structure and composition were the strongest and most consistent drivers of hotspots. Other factors varied in their importance by region, reflecting regional differences in biophysical context. Relative to the predictor variables included in our models, estimated spatio-temporal random effects were more closely correlated with model predictions, suggesting that dynamic factors such as outbreak spread strongly shape patterns of biotic disturbance hotspots. Our results illustrate the widespread nature of biotic disturbance hotspots across western US coniferous forests and demonstrate the importance of forest structure and regional outbreak dynamics in anticipating hotspots at regional scales. These findings provide a deeper understanding of interacting forest disturbances and have important implications for the resilience of forests during a period marked by continued increases in disturbance activity.