We assessed the influence of island isolation on the composition of insular bird assemblages with a particular focus on species traits associated with dispersal. To do so, we tested whether ecomorphological metrics of dispersal ability, namely hand-wing index and Kipp's distance, increase with increasing island isolation.
Global.
Birds.
We integrated global datasets of island characteristics with distribution and ecomorphological trait information of birds; our final dataset comprised information for 2034 native, resident and terrestrial species inhabiting 2399 islands. Species restricted to islands were removed to avoid potentially confounding effects of speciation, such as the evolution of flightlessness or poor flight on islands. Using the generalised additive models, we tested for the relationship between hand-wing index or Kipp's distance and island isolation, accounting for the effects of island area and spatial autocorrelation. We performed the analyses separately for (i) continental and oceanic islands and (ii) for all terrestrial birds and for passerine birds only.
Hand-wing index and Kipp's distance were positively related to island isolation on oceanic islands, that is bird communities on more isolated oceanic islands were composed of species with wings that had a higher aspect ratio and were more elongated. However, this relationship did not hold for continental islands. We found these patterns to be consistent for all terrestrial birds as well as for passerine birds only.
Our study provides strong evidence that island isolation influences the trait composition of island bird assemblages at a global scale. Our results highlight the variation of dispersal-related ecomorphological traits among bird assemblages on islands, suggesting that these traits play an important role in mediating the influence of island isolation on community assembly processes on islands.
An ecological community consists of species of various abundances that reflect their responses to the environmental conditions. A classic macroecological pattern, the species abundance distribution (SAD), has been studied for diverse taxa and communities and integrated into numerous modelling tools. Despite its widespread use, a mathematical model that can capture variations in the empirical SAD and describe its response to environmental changes is still lacking. By integrating the Maximum Entropy Theory of Ecology (METE) with a generalised entropy called Rényi's entropy, we aim to develop a new ecoinformatic model that can predict the variation of empirical SAD along multiple environmental gradients.
Panama.
Angiosperms.
We extend the METE using the Rényi's entropy as an uncertainty measure. We apply this extended METE, called Rényi model, to the tree abundance data from 49 plots in Panama and predict the SAD within each plot. We estimate Rényi's parameter q by fitting the predicted SAD to the empirical SAD in each plot. We further compile climate and soil data from the Panama plots and analyse their relationships with the estimated q using multiple regressions.
Rényi model provides adequate description of the empirical SADs and outperforms lognormal or log-series models in 40 of the 49 tree plots, according to the Akaike information criterion. Variations in Renyi's q estimates (from 1/2 to 1) reflect shifts in the empirical SADs. Multiple regressions reveal that P, Al and NH4, three soil chemicals that are important for tree growth and species distribution, significantly affect Renyi's q across plots.
These findings suggest that the Rényi model and Rényi's q can characterise the SAD of communities under environmental changes. They also indicate the potential of using generalised entropies to predict macroecological patterns in stressed ecosystems.
Ecologically similar species living in sympatry are expected to segregate to reduce the effects of competition where resources are limiting. Segregation from heterospecifics commonly occurs in space, but it is often unknown whether such segregation has underlying environmental causes. Indeed, species could segregate because of different fundamental environmental requirements (i.e., ‘niche divergence’), because competitive exclusion at sympatric sites can force species to either change the habitat use they would have at allopatric sites (i.e., ‘niche displacement’) or to avoid certain areas, independently of habitat (i.e., ‘spatial avoidance’). Testing these hypotheses requires the comparison between sympatric and allopatric sites. Understanding the competitive mechanisms that underlie patterns of spatial segregation could improve predictions of species responses to environmental change, as competition might exacerbate the effects of environmental change.
North Atlantic and Arctic.
Common guillemots Uria aalge and Brünnich's guillemots Uria lomvia.
Here, we examine support for these explanations for spatial segregation in two closely-related seabird species, common guillemots (Uria aalge) and Brünnich's guillemots (U. lomvia). For this, we collated a pan-Atlantic data set of breeding season foraging tracks from 1046 individuals, collected from 20 colonies (8 sympatric and 12 allopatric). These were analysed with habitat models in a spatially transferable framework to compare habitat preferences between species at sympatric and allopatric sites.
We found no effect of the distribution of heterospecifics on local habitat preferences of the focal species. We found differences in habitat preferences between species, but these were not sufficient to explain the observed levels of spatial segregation at sympatric sites.
Assuming we did not omit any relevant environmental variables, these results suggest a mix of niche divergence and spatial avoidance produces the observed patterns of spatial segregation.
Australia's distinct geological history provides key insights into the diversity of its flora. While previous studies have predominantly focused on climate as the main driver of species richness, growing evidence suggests that geological factors also play an important role. This study aims to investigate the influence of Cenozoic volcanic lithologies on terrestrial vascular plant diversity in eastern Australia, disentangling the relative contributions of climate and geology to biodiversity patterns.
Eastern Australia.
Terrestrial vascular plants.
We assessed the patterns of species richness in this region by examining whether sites with Cenozoic volcanic lithologies harbour greater vascular plant diversity, using a permutational multivariate analysis of variance (PERMANOVA). We then used a supervised machine learning algorithm (decision trees) coupled with partial canonical correspondence analysis (CCA) to discriminate the environmental variables influencing species richness and site composition in 230 sites in Queensland, New South Wales, Victoria and Tasmania.
Soil profile variability and terrain ruggedness, influenced by underlying volcanic lithologies, emerged as primary predictors of species richness. We found species composition, indicative of distinct ecological communities, showed greater similarity within lithological types and varied significantly across volcanic complexes at different latitudes. Notably, areas of higher species richness corresponded with a greater diversity of stratigraphic units within protected zones.
Our study reveals a significant imprint of Cenozoic volcanic activity on present-day plant species richness and distribution in eastern Australia. We show that geological features, particularly lithology and site complexity, play a crucial role in shaping species richness beyond previously recognised climatic factors. These findings highlight the importance of integrating geological and edaphic factors into conservation strategies, thereby broadening our understanding of ecological dynamics, and guiding more effective biodiversity conservation.
To examine the species richness, distribution and macroecological patterns of elasmobranch assemblages across a broad latitudinal gradient in the Eastern Pacific Ocean (EPO).
The study area encompasses the Pacific coast of the American continent, spanning from 65°N to 60°S, and extending from the coastline to approximately 1000 km offshore, encompassing the oceanic archipelagos.
Elasmobranchs.
Utilising the established distribution ranges of 190 elasmobranch species (comprising 89 sharks and 101 rays), we assessed the richness and spatial distribution of these species across the EPO. Subsequently, three macroecological patterns were scrutinised: Rapoport's rule, the Mid Domain Effect with its association to Mean Sea Surface Temperature, and the correlation between body size and latitudinal distribution.
The analysis of species richness along latitudinal gradients unveiled a bimodal pattern, reaching peaks between 30° to 20°N and 10°N to 5°S. A decline in species richness was observed from tropical to polar regions. Contrary to Rapoport's Rule, Stevens' and midpoint methods demonstrated higher geographic range values at lower latitudes, diminishing towards higher latitudes. Additionally, the mid-domain effect model exhibited a robust correlation with the mean sea surface temperature. Exploring the interspecific relationship between body size and extent of occurrence, it was found that 29 out of 190 species are more susceptible to extinction.
Marine elasmobranchs of the EPO defy conventional latitudinal richness patterns and deviate from Rapoport's rule. Furthermore, our findings indicate a robust correlation between observed richness and both sea surface temperature and environmental heterogeneity. The proportion of species vulnerable to human or stochastic impacts potentially leading to extirpation in relation to their geographic range was low across the majority of examined provinces.
The combined influences of demographic dynamics and gene flow on local adaptation in plants is still poorly understood. Here, we used a genome scan approach on three closely related Neotropical palms, Acrocomia aculeata, A. intumescens and A. totai, to identify the evolutionary processes generating shared and lineage-specific patterns of differentiation and selection across the genomic landscape.
Amazonia, Atlantic Forest, Cerrado and Caatinga ecoregions of Brazil.
Arecaceae.
We used target sequence capture and analysis of climatic correlation, detection of selective sweeps, balancing selection, and spatial and non-spatial models to identify signatures of natural selection and admixture. We also determined temporal dynamics in spatial distribution and demographic changes.
We found a higher number of lineage-specific than shared adaptive sites (SNPs) and no evidence of selective sweeps in shared genes, suggesting lineage specific natural selection across species. Further, evidence of balancing selection in several genes was also identified in the three species. Niche-based and coalescent models suggest that shifts in spatial range during the Quaternary caused overlapping distributions between species, leading to hybridisation between parapatric localities.
Interspecific hybridisation may have spread both neutral and adaptive SNPs, which may explain the shared adaptive genes between species. Taken together, we show how genomic adaptation can occur despite introgression, through evolutionary processes that likely drive similar patterns of adaptation in other organisms.
To test if temperature significantly influences the global biogeographic distribution of marine epifaunal bivalves via their skeletal mineralogy.
Global.
Marine, epifaunal bivalves.
The skeletal mineralogy of 45,789 epifaunal bivalve occurrences from 669 species from the Ocean Biodiversity Information System (OBIS) was related to sea surface temperatures from Bio-ORACLE. Binomial regression was used to assess the influence of temperature and seasonality on the distribution of aragonitic and calcite-secreting bivalve occurrences, aggregated in equal-area grid cells.
The proportion of aragonitic bivalve occurrences significantly increases with mean annual temperature in our global analysis and most marine biogeographic realms. A greater prevalence of calcite-secreting bivalves in seasonal climates could be shown at low mean annual temperatures at the global scale but not within biogeographic realms.
The global biogeographic distribution of epifaunal bivalves is significantly influenced by water temperature via their skeletal mineralogy. The mechanism driving this pattern is best explained by the temperature modulation of the effect of Mg2+ on calcite growth. Although this Mg2+ effect predicts an advantage for aragonite secretion at higher temperatures, poleward migration in response to higher temperature extremes will expose tropical taxa to cooler temperatures in the cold season, which may impede aragonite secretion in taxa not adapted to these climates.
Our results suggest that skeletal mineralogy is likely to influence ocean warming-induced migration patterns.
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