Area, isolation and climate explain the diversity of mammals on islands worldwide

Barreto et al. (2021) – Proceedings B

Insular biodiversity is expected to be regulated differently than continental biota, but their determinants remain to be quantified at a global scale. We evaluated the importance of physical, environmental, and historical factors on mammal richness and endemism across 5592 islands worldwide. We fitted generalized linear and mixed models to accommodate variation among biogeographic realms and performed analyses separately for bats and non-volants. Richness on islands ranged from one to 234 species, with up to 177 single island endemics. Diversity patterns were most consistently influenced by the islands’ physical characteristics. Area positively affected mammal diversity, in particular the number of non-volant endemics. Island isolation, both current and past, was associated with lower richness but greater endemism. Flight capacity modified the relative importance of past versus current isolation, with bats responding more strongly to current and non-volant mammals to past isolation. Biodiversity relationships with environmental factors were idiosyncratic, with a tendency for greater effects sizes with endemism than richness. The historical climatic change was positively associated with endemism. In line with theory, we found that area and isolation were among the strongest drivers of mammalian biodiversity. Our results support the importance of past conditions on current patterns, particularly of non-volant species.


Turnover-driven loss of forest-dependent species changes avian species richness, functional diversity, and community composition in Andean forest fragments

Jones et al. (2021) – Global Ecology and Conservation

Andean forests, a hotspot of biodiversity, have suffered extensive fragmentation, yet we have little understanding of how this process has affected biodiversity. We surveyed bird communities across a gradient of fragment sizes (10–170 ha) and a continuous forest reference site in the Colombian Western Andes. Using a multi-species occupancy model to combine survey data from audio-visual transect surveys, mist-netting, and playbacks for owls, we estimated alpha and beta taxonomic and functional diversity. We asked whether (1) habitat amount (patch size), edge effects, or selective logging affect bird occupancy and drive changes to diversity, (2) functional and taxonomic diversity respond similarly to fragmentation, and (3) compositional changes result from species turnover or nested species loss. Species richness declined with decreasing habitat amount, increasing edge density, and increasing disturbance through selective logging. These effects were driven by the loss of forest-dependent species, which were also area sensitive: 30 such species were absent from fragments, even the largest ones (>150 ha). Area-sensitive species were also edge sensitive and increased in occupancy in unlogged forest. We further found high beta diversity (0.78) driven by species turnover (85% of dissimilarity) along the gradient. Despite extensive turnover to non-forest species within functional groups, functional trait richness and dispersion significantly declined with habitat amount. Small fragments may mimic the structure and composition of early-successional Andean forests, driving spatial turnover patterns favoring disturbance-adapted species at the expense of primary-forest specialists. Large forest reserves are therefore required to conserve forest-dependent Andean birds.


Spatial variation in direct and indirect effects of climate and productivity on species richness of terrestrial tetrapods

Barreto et al. (2021) – Global Ecology and Biogeography

We aimed to dissect the spatial variation of the direct and indirect effects of climate and productivity on the global species richness of terrestrial tetrapods. We used a geographically weighted path analysis to estimate and map the direct and indirect effects of temperature, precipitation and primary productivity on species richness of terrestrial tetrapods across the globe. We found that all relationships shift in magnitude, and even in direction, among taxonomic groups, geographical regions and connecting paths. Direct effects of temperature and precipitation are generally stronger than both indirect effects mediated by productivity and direct effects of productivity. Richness gradients seem to be driven primarily by the effects of climate on organismal physiological limits and metabolic rates rather than by the amount of productive energy. Reptiles have the most distinct relationships across tetrapods, with a clear latitudinal pattern in the importance of temperature versus water.


Quantitative genetics of extreme insular dwarfing: The case of red deer on Jersey

Diniz-Filho et al. (2021) – Journal of Biogeography

The Island Rule—that is, the tendency for body size to decrease in large mammals and increase in small mammals on islands has been commonly evaluated through macroecological or macroevolutionary, pattern-orientated approaches, which generally fail to model the microevolutionary processes driving either dwarfing or gigantism. Here, we seek to identify which microevolutionary process could have driven extreme insular dwarfism in the extinct dwarf red deer (Cervus elaphus) population on the island of Jersey, UK (Channel Islands). We applied an individual-based quantitative genetics model parameterized with red deer life-history data to study the evolution of dwarfism in Jersey’s deer, considering variations in island area and isolation through time due to sea-level changes. The body size of red deer on Jersey decreased fast early on, due to phenotypic plasticity, then kept decreasing almost linearly over time down to the actual
body size of the Jersey deer (36 kg on average). Only 1% of 10,000 replicates failed to reach that size in our simulations. The distribution of time to adaptation in these simulations was right-skewed, with a median of 395 generations (equivalent to roughly 4 kyr), with complete dwarfism effectively occurring in less than 6 kyr 84.6% of times. About 72% of the variation in the time to adaptation between simulations was collectively explained by higher mutational variance, the number of immigrants from the continent after isolation, available genetic variance, heritability, and phenotypic plasticity. The extreme dwarfing of red deer on Jersey is an expected outcome of high mutational variance, high immigration rate, a wide adaptive landscape, low levels of inbreeding, and high phenotypic plasticity (in the early phase of dwarfing), all occurring within a time window of around 6 kyr. Our model reveals how extreme dwarfism is a plausible outcome of common, well-known evolutionary processes.


Environmental niche and functional role similarity between invasive and native palms in the Atlantic Forest

Bello et al. (2020) – Biological Invasions

Invasive species can significantly affect native species when their niches are similar. Ecological and morphological similarities between the invasive Australian palm, Archontophoenix cunninghamiana, and the native palm from the Brazilian Atlantic Forest, Euterpe edulis, suggest that they have similar environmental requirements and functional roles (i.e., the function a species performs in an ecosystem). This similarity raises concerns about how the invasive palm could impact the native species in the present and future. We used spatial (species occurrences) and ecological information (frugivory events) to characterize the environmental niche and functional role of the two palms and assess their overlap. In addition, we predicted the potential area of occurrence of each palm within the Brazilian Atlantic Forest under current and future climate conditions. We estimated the environmental conditions used by the invasive plant based on its native distribution only and based on all areas where the species is able to establish across the globe. We found that the environmental niches of the two palm species overlap up to 39%, which corresponds to 50% of the current geographic distribution of E. edulis in the Atlantic Forest. In the areas where the two species potentially co-occur, the impact of the invasive species on the native should be influenced by the invasive species interactions with frugivores. We found that the frugivory functional role of the two palms was similar (84% overlap) which suggests that A. cunninghamiana might disrupt the seed dispersal of the native palm. However, co-occurrence between the palms may decline with future climate change, as the potential environmental suitable area for the invasive palm is predicted to decline by 10% to 55%. Evaluating the similarity in both the environmental niche, of the native and global extent, and the functional role of native and invasive plants provides a detailed understanding of the potential impact of invasive species on native species now and in the future.


Environmental factors explain the spatial mismatches between species richness and phylogenetic diversity of terrestrial mammals

Barreto, Graham & Rangel (2019) – Global Ecology and Biogeography

We explored the spatial variation of the relationships between species richness (SR), phylogenetic diversity (PD) and environmental factors to infer the possible mechanisms underlying patterns of mammalian diversity in different regions of the globe. We used a hexagonal grid to map SR and PD of mammals and four environmental factors (temperature, productivity, elevation and climate‐change velocity since the Last Glacial Maximum). We related those variables through direct and indirect pathways using a novel combination of path analysis and geographically weighted regression to account for spatial non-stationarity of path coefficients. We found that species richness, PD and environmental factors relate differently across the geographical space, with most relationships varying in both magnitude and direction. Species richness is associated with lower PD in much of the tropics and in the Americas, which reflects the tropical origin and the recent diversification of some mammalian clades in these regions. Environmental effects on PD are predominantly mediated by their effects on SR. But once richness is controlled for, the relationships between environmental factors and PD (i.e., PDSR) highlight environmentally driven changes in species composition. Environmental–PDSR relationships suggest that the relative importance of different mechanisms driving biodiversity shifts spatially. Across most of the globe, temperature and productivity are the strongest predictors of richness, whereas PDSR is best predicted by temperature. In conclusion, richness explains most spatial variation in PD, but both dimensions of biodiversity respond differently to environmental conditions across the globe, as indicated by the spatial mismatches in the relationships between environmental factors and these two types of diversity. We show that accounting for spatial non‐stationarity and environmental effects on PD while controlling for richness uncovers a more complex scenario of drivers of biodiversity than previously observed.


PALEO-PGEM v1.0: a statistical emulator of Pliocene–Pleistocene climate

Holden et al. (2019) – Geoscientific Model Development

We describe the development of the “Paleoclimate PLASIM-GENIE (Planet Simulator–Grid-Enabled Integrated Earth system model) emulator” PALEO-PGEM and its application to derive a downscaled high-resolution spatiotemporal description of the climate of the last 5 x 106 years. The 5 x 106-year time frame is interesting for a range of paleo-environmental questions, not least because it encompasses the evolution of humans. However, the choice of time frame was primarily pragmatic; tectonic changes can be neglected to first order, so that it is reasonable to consider climate forcing restricted to the Earth’s orbital configuration, ice-sheet state, and the concentration of atmosphere CO2. The approach uses the Gaussian process emulation of the singular value decomposition of ensembles of the intermediate-complexity atmosphere–ocean GCM (general circulation model) PLASIM-GENIE. Spatial fields of bioclimatic variables of surface air temperature (warmest and coolest seasons) and precipitation (wettest and driest seasons) are emulated at 1000-year intervals, driven by time series of scalar boundary-condition forcing (CO2, orbit, and ice volume) and assuming the climate is in quasi-equilibrium. Paleoclimate anomalies at climate model resolution are interpolated onto the observed modern climatology to produce a high-resolution spatio-temporal paleoclimate reconstruction of the Pliocene–Pleistocene.


Drivers of geographic patterns of North American language diversity

Coelho et al. (2019) – Proceedings B

Although many hypotheses have been proposed to explain why humans speak so many languages and why languages are unevenly distributed across the globe, the factors that shape geographical patterns of cultural and linguistic diversity remain poorly understood. Prior research has tended to focus on identifying universal predictors of language diversity, without accounting for how local factors and multiple predictors interact. Here, we use a unique combination of path analysis, mechanistic simulation modelling, and geographically weighted regression to investigate the broadly described, but poorly understood, spatial pattern of language diversity in North America. We show that the ecological drivers of language diversity are not universal or entirely direct. The strongest associations imply a role for previously developed hypothesized drivers such as population density, resource diversity, and carrying capacity with group size limits. The predictive power of this web of factors varies over space from regions where our model predicts approximately 86% of the variation in diversity, to areas where less than 40% is explained.


Canopy height explains species richness in the largest clade of Neotropical lianas

Meyer et al. (2019) – Global Ecology and Biogeography

Tall and structurally complex forests can provide ample habitat and niche space for climbing plants, supporting high liana species richness. We test to what extent canopy height (as proxy of 3D habitat structure), climate and soil interact to determine species richness in the largest clade of Neotropical lianas. We expect that the effect of canopy height on species richness is higher for lianas from closed tropical rainforests compared to riparian and savanna habitats. We used structural equation models to evaluate direct and indirect effects of canopy height, climate (temperature, precipitation and precipitation seasonality), and soil (cation exchange capacity and soil types) on overall Bignonieae species richness (339 liana species), as well as on species richness of lianas from forest, riparian and savanna habitats, respectively. We further performed multiple regression models with Moran’s eigenvector maps to account for spatial autocorrelation. Canopy height was a key driver of liana species richness, in addition to climate and soil. Both, overall species richness and forest species richness showed a strong positive relationship with canopy height whereas the relationship was less pronounced for riparian species. Richness of savanna species even decreased with increasing canopy height. Climate also explained a substantial proportion of variation in liana species richness whereas soil variables showed little explanatory power. The relationship between canopy height and liana species richness differs among habitats. While forest and riparian lianas probably benefit from physical support to reach the forest canopy to escape low light availability in the understory, a high light availability in open habitats and an increased risk of embolism of conductive vessels for lianas with long stems living in areas with high seasonality might explain the inverse relationship between species richness and canopy height in savannas.