Ecography最新文献

Understanding how the remarkable biodiversity of the American tropics developed has been a long-standing question, yet knowledge gaps remain. Previous studies examined the roles of bioregions in shaping diversity patterns but often overlooked speciation, a critical driver of species richness, and insufficiently accounted for temporal changes in speciation and dispersal dynamics. To address this, we investigated the temporal mechanisms of speciation and dispersal that have shaped diversity in the American tropics using ferns (Polypodiopsida) as a model group across nine bioregions. We employed biogeographic stochastic mapping (BSM) and a large-scale phylogenetic tree alongside extensive occurrence records to infer historical patterns of speciation and dispersal. We find that the American tropics function as a biogeographical maze composed of interconnected corridors, characterised by high emigration and immigration rates, rather than isolated regions. The Andes emerged prominently as a biodiversity radiator, playing a dual role by generating substantial species richness through speciation and acting as a primary source of dispersal to neighbouring regions. This unique position underscores the Andes' pivotal role in structuring fern diversity across the American tropics, contrasting with the Amazonian-centred patterns typically observed in angiosperms. Our findings highlight the critical importance of considering speciation and historical contexts in relation to changing environments when interpreting patterns of tropical biodiversity.

There is much contention over the causes and correlates of megafaunal extinctions at the end of the Pleistocene. A major role for human impact such as hunting has been discussed widely. If correct, the overkill hypothesis explains not only why large mammals in general were highly prone to extinction but suggests that extinction may have been selective within large mammals. Among other things, it has been argued that extinct large mammals tended to be large and have small brains. Here we test these hypotheses using a comprehensive global dataset of 22 ecological and life history traits mapped to 120 living and 14 extinct carnivore species. The data document occurrences within 260 distinct fossil assemblages that span the Late Pleistocene and Holocene. To address collinearity and phylogenetic autocorrelation, we first perform least-squares orthogonalisation of the predictor variables and then use phylogenetic comparative methods to carry out regressions. Only basal metabolic rate and diurnality are robust predictors of extinction, even after accounting for phylogenetic and trait uncertainty. Furthermore, we show that living carnivores with high metabolic rates are more likely to be threatened and address the implications for conservation and the current extinction crisis.

The effects of habitat condition on biodiversity have primarily been investigated using discrete (patch-matrix) habitat models, which consider habitat fragments as islands embedded in an inhospitable matrix. Recently, continuum habitat models, which focus on ecological gradients without defining habitat or matrix, have emerged. However, no formal comparison between patch-matrix, continuum, and hybrid habitat models (which combine characteristics of both) has been undertaken globally. Here, we compared the ability of patch-matrix, continuum, and hybrid models of habitat intactness to explain the risk of extinction for terrestrial mammals on a global scale. We found that hybrid models consistently outperform both patch-matrix and continuum models of habitat intactness in predicting extinction risk, regardless of a species' habitat specialization. Moreover, the magnitude of the relationship between habitat intactness and extinction risk was strongest when using hybrid habitat models. Our results suggest that combining discrete habitat patches with gradients of habitat condition, influenced by the surrounding matrix, can improve extinction risk analyses and provide valuable insights for conservation efforts.

Hawaii has experienced profound declines in native avifauna alongside the introduction of numerous bird species. While site-specific population studies are common, landscape-level analyses of avian population dynamics are rare, particularly in island ecosystems. To address this gap, we used a density surface model to create a spatio-temporal projection of population densities and distributions across the Island of Hawai‘i, spanning nearly five decades (1976–2023). We incorporated environmental covariates of habitat, precipitation, and elevation, to further refine our projections. Our analysis encompassed nine native and six non-native bird species, inhabiting a range of ecological niches. We found five out of nine native species have declined in density and range size while four were stable. For non-native species, two were stable, one was decreasing, and three were increasing in density and range size. Our landscape projections can inform management by suggesting areas critical for habitat preservation and land acquisition for conservation, identifying where range fragmentation is occurring, and pinpointing locations of multi-species declines that are likely driven by a common cause. Our study demonstrates how long-term, landscape-level monitoring and analyses can advance understanding and addressing biodiversity loss, particularly in vulnerable tropical island ecosystems.

Many of the world's megafaunal species went extinct during the late Quaternary, leading to dramatic reductions in community and ecosystem functioning. While the nature and severity of the extinctions are well documented on global and continental scales, less is known about local-scale impacts. We quantified the biomass and energy use of 292 pre-extinction and 360 post-extinction fossil assemblages from around the globe to determine effects on large mammal communities. Assemblage energy use was calculated from metabolic rates obtained for 562 individual species, and was compared to species richness along with indicators of taphonomy, archaeology, and biogeography, using three analytical methods: least-squares orthogonalization regression, spatial autoregression, and linear mixed effects model analysis. Globally, total biomass and energy use are greatly reduced in post-extinction assemblages. Human-accumulated assemblages are further homogenised post-extinction due to their high abundances of domesticated species. The presence of domesticates greatly altered the biomass and energy use of assemblages post-extinction, producing strong energetic variation across continents that differs considerably to pre-extinction patterns. This fundamental anthropogenic alteration of communities further exacerbated the impacts of Pleistocene extinctions, even in less severely impacted regions. The results show how human activities have altered mammalian communities for many thousands of years.

Mountains are home to steep elevational gradients in environmental factors, biodiversity and ecosystem functionality. Though these gradients are tightly connected, little is known about the relative contribution of environmental and biotic factors in driving elevational changes in ecosystem functionality. Here, we conducted a comprehensive survey of three > 2000 m long elevational gradients within the Hengduan Mountains region (southern China), quantifying key metrics of ecosystem functionality, as well as community composition and species richness of both plants and soil microbes. We found significant elevational patterns of plant and bacterial richness and ecosystem functionality, varying from unimodal (hump-shaped or U-shaped) to monotonic (linear) among the three mountains. Unexpectedly, plant and bacterial richness were either negatively or not significantly correlated with key indicators of ecosystem functionality. We further demonstrated that climate and soil pH were the key predictors of ecosystem functionality. Ecosystem functionality was additionally affected by changes of the bacterial species composition. Our results suggest that climate and microbial community composition jointly drive elevational changes in ecosystem functionality, with no clear role for species richness per se. These findings advance our understanding of mountain biogeography and the links between biodiversity and ecosystem function.

The center–periphery hypothesis (CPH) states that species' demographic performance declines from the center towards the periphery of their geographic range due to increasingly suboptimal environmental conditions. We tested the predictions under the CPH using two lizard lineages with different activity patterns and distributions, taking lizard body condition and gastrointestinal parasitism as proxies of demographic performance. We sampled Ameiva ameiva, Tropidurus itambere, and T. madeiramamore from core localities and peripheral Cerrado isolates in southwestern Amazonia. To assess predictions under the CPH, we built generalized linear mixed models using the indicators of demographic performance as the response variables. Environmental (climate, elevation, soil) and spatial (landscape parameters, distance to Cerrado's center and periphery) variables were predictor variables, along with lizard genus and their interactions. We applied generalized dissimilarity modeling (GDM) and variance partitioning to assess geographic, environmental, and spatial influences on parasite beta diversity. Lizard lineage was the most important predictor of body condition and lizard parasite abundance/richness. Centrality, connectivity, and precipitation of the warmest quarter significantly predicted lizard gastrointestinal parasitism. Soil, centrality, landscape, and elevation had a non-zero sum of coefficients in GDM's I-spline for lizard parasite beta diversity. Geographic distance had a negligible influence, and environmental variation was the primary driver of parasite beta diversity. For Ameiva, demographic performance did not vary across the sampled central and peripheral areas, both central to Ameiva's distribution, consistent with CPH predictions of stable demographic performance between central areas. Tropidurus displayed better body condition and higher parasite abundance in peripheral isolates, contrary to predictions under the CPH, likely due to ecological release. Soil and proximity to the Cerrado's center were the strongest predictors of parasite beta diversity, suggesting environmental and spatial factors outweigh biotic or climatic influences. These results suggest that the CPH's predictions may not always hold, especially when ecological release affects demographic performance.

Global change will impact the distribution and abundance of predators through a combination of abiotic variables, such as temperature; and biotic variables, such as prey availability. However, there is a poor understanding of how distribution projections with biotic variables differ from those with abiotic variables, particularly in resource-limited marine systems. We address this knowledge gap using the planktonic larvae of iconic and economically important pelagic fish predators. We leverage a multidecadal, long-term sampling program from the western Atlantic Ocean to assess the efficacy of using zooplankton prey (copepods, larvaceans and cladocerans) and climate variables to predict the distribution of larvae of seven pelagic fish species, including tunas, billfishes and mahi-mahi. Zooplankton prey, particularly larvaceans, showed high importance for predicting the distribution of smaller tunas. Temperature showed high importance for true tuna Thunnus spp., billfish and mahi-mahi. Statistical models linking predator, prey and abiotic variables were forced with climate projections from an ensemble of earth system models to assess zooplankton and fish larvae distribution changes. Redistributions and declines of zooplankton prey led to minimal changes in abundance and distribution for most larval taxa. However, direct climate change effects, driven partially by ocean warming, led to increases in abundance and northward distribution shifts for multiple larval taxa. These climate change–zooplankton–fish larvae relationships highlight that future distribution and abundance changes of predators can be dampened when assessing impacts of prey availability changes. We also show that in a resource-limited system, key pelagic predators, many of which produce lucrative fisheries, are spatiotemporally linked with their preferred zooplankton prey.

Biogeographical partitioning of ecological communities has been renewed in recent decades to illustrate broad distributional patterns. In the oceans, observational datasets have grown substantially and open new access to test bioregional patterns beyond classically fixed thresholds of endemism to differentiate regions. This work combines a recently collated dataset of 29 different scientific bottom trawl surveys spanning 21 years with network-based clustering to illustrate biogeographical partitions of vast tracts of the Northern Hemisphere's continental shelf seas. Our work contributes to testing bioregionalization patterns in demersal fishes using observational data, totaling 138 227 trawls and > 1700 species, with bipartite network clustering weighted by species occurrence frequencies. We propose eight major biogeographical partitions of marine demersal fish communities across shelf seas in the Northern Hemisphere. These patterns capture known biogeographical boundaries (e.g. North Sea–Baltic Sea, Cape Hatteras) alongside potential transition areas deduced from uncertainty estimates based on shared network nodes between bioregions. The most species-rich areas include the Southeast US Shelf, Temperate Pacific, Northeast Atlantic Shelf, and the Outer European Shelf – corresponding to relatively high endemicity. However, the relatively species-poor partitions including the Baltic Sea and the North and Celtic Seas display comparatively low endemicity (~10%), illustrating apparent statistical differences in partitions captured by bipartite networks and occurrence frequencies that would otherwise be missed using a fixed endemic criterion. Our proposed bioregionalization can be compared against the growing availability of species occurrence data, dispersal limitations, or other quantitative observations of ecological communities.