Ecography最新文献

Amphibians exhibit a large diversity in reproductive and developmental strategies, which in turn are linked to their body size, life history and habitat. Here, we explore why terrestrial egg laying frogs are on average smaller than aquatic egg laying ones and whether this pattern also exists in salamanders. We hypothesized that egg deposition site and body mass are not linked directly across species, but that terrestrial egg layers occur in climates and use microhabitats that favor small masses. To test this, we compiled a dataset on egg deposition site (terrestrial or aquatic), development mode (biphasic with larvae or direct development without larvae), body mass, microhabitat use (water-dependent, ground-dwelling or arboreal) and climate within their distribution area (temperature, precipitation and seasonality in both) of 3091 frog and 244 salamander species. We analyzed the interrelations between these traits and environmental factors by using a cross-species approach and phylogenetic generalized least squares analysis. Body masses increased along a gradient from warm, humid and unseasonal climates to cold, dry and seasonal climates in frogs and salamanders. Terrestrial egg deposition was constrained to warm, humid and unseasonal climates only in frogs. Terrestrial eggs and an arboreal microhabitat use were linked in frogs and salamanders, and arboreal frogs were smaller than non-arboreal ones. We confirmed that frogs with terrestrial eggs had smaller average body masses than those with aquatic eggs, irrespective of their development mode, but this difference disappeared when we corrected body masses for the effects of climate and microhabitat use. In salamanders, however, egg deposition site and development mode were neither directly related to body mass, nor indirectly via the effects of climate and microhabitat use. Our results suggest that thermal and hydric environmental conditions determine the geographical distribution of body mass and reproductive strategies in amphibians and set the framework for their evolution.

The positive relationship between species richness and area is regarded as one of the few laws in ecology. Therefore, deviations from predictable species–area scaling, evident as high residual variance in species–area curves, are often interpreted as anomalous behaviour. Small-island systems often do not conform to species–area relationships, yet the high stochasticity in their species–area curves is frequently treated as unexplainable noise or attributed to idiosyncratic extinction rates. Here, we introduce a statistical framework that incorporates the degree of stochasticity in species–area relationships as an explicit, interpretable model parameter. Using a global island plant dataset for atolls (378 islands across 19 atolls) – prototypical examples for small-island dynamics – we show that the degree of residual variance in species–area curves can be captured, modelled, and linked to environmental conditions. Our heteroscedastic modelling approach demonstrates that apparent stochasticity in species–area relationships is not random but predictable through environmental drivers. Specifically, we found that increased rainfall reduces the residual variance around the species–area curve, indicating that resource availability is a critical factor enabling conformity to species–area scaling. Cyclone disturbance frequency did not drive stochasticity, challenging the prevailing view that disturbance regimes drive the stochasticity in species–area scaling on small islands. By treating residual variance as an explicit model parameter in species–area relationships rather than unexplainable noise, our approach provides new insights into the conditions enabling biological communities to conform to species–area scaling. Shifting the focus in species–area studies on the residual variance as an interpretable model parameter that captures the degree of conformity to species–area scaling offers novel perspectives into the environmental factors prerequisite for species–area scaling. This contributes to unifying the apparent anomalous, stochastic nature of small-island systems with the general law of linear species–area scaling.

Boreal and tundra plant communities are expected to change in biodiversity due to increasing global change pressures such as climate warming. One long-term scenario is increasing compositional similarity, i.e. biotic homogenization, which has been relatively little studied in high-latitude plant communities. Here, we study how the composition and diversity of heathland and tundra plant communities have changed in northern Fennoscandia over several decades. In 2013–2023, we resurveyed 275 historic vegetation plots, originally surveyed in 1964–1975, with percentage covers for vascular plant, bryophyte and lichen species. We analyzed temporal changes in community composition and diversity across the study area and in different biogeographic zones, continentality-humidity classes and habitat types. We found a strong homogenization trend across the study area, with plant communities becoming more similar in composition over the decades when all taxa were treated together. The observed homogenization was driven especially by the increased similarity of vascular plant and lichen communities and was largely independent of biogeographic zones or continentality-humidity gradient. Homogenization was particularly associated with the drastic encroachment of the evergreen dwarf shrub Empetrum nigrum in habitat types originally dominated by other species, and with the decrease in lichen cover. In general, our findings suggest that Fennoscandian heathland and tundra vegetation is transforming towards a more homogeneous evergreen dwarf shrub-dominated system, which may threaten ecosystem multifunctionality. Our results highlight the importance of exploring biodiversity among different metrics and growth forms to understand the overall changes in heathland and tundra biodiversity.

Between the 16th and the 20th centuries, European countries established vast colonial empires on all continents. These empires triggered profound environmental, demographic and economic transformations. It is likely that many non-native species have benefited from the newly emerged trade network between European countries and their colonies to spread to new regions, leading to an increase in invasions across countries that belonged to these empires. However, this hypothesis has not been tested, and it is still unknown whether colonial empires influenced non-native species richness and invasion dynamics over the last centuries. Here, we show that prior to 1960, countries that belonged to a colonial empire received more than twice as many non-native ant species than those that did not. During that period, ant species native to parts of an empire spread preferentially to other countries within the same empire. However, after 1960 former colonial ties had no longer an effect on ant introductions. We also found that colonized countries were the most important source of non-native ants, contradicting the ‘Imperialist dogma'. Overall, our findings show that ant invasion dynamics were shaped by the rise and fall of European colonial empires, transitioning from empire-centered invasions before 1960 to a truly global spread of species in the more recent decades.

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.