Frontiers of Biogeography

The longstanding view of Neotropical mountain uplift as a promoter of species diversification has become commonplace in the last decades and could benefit from more specific Earth-Life evolution associations. We now know that mountain formation has contributed to the outstanding levels of richness and endemism of Neotropical mountains. Nonetheless, we are lacking conceptual and empirical frameworks where geological and biological processes are causally linked through testable hypotheses. In this perspective, we present volcanic activity in the Neotropics, not as phenomena occurring “on top of” mountain uplift, the latter being the phenomena of biogeographical interest, but rather as geological processes that directly impact biodiversity and are themselves the phenomenon of biogeographical interest. Volcanoes deserve biogeographical attention because their effects on landscape evolution generate predictable biodiversity process counterparts that can be integrated into biogeographical models enabling hypothesis testing. We review examples in the literature emphasizing the spatio-temporal scale of volcanism’s predicted and recorded effects on biodiversity. We illustrate our perspective by two recent study cases, focusing on wax palms and passerine birds. In the first one, wax palm genomic sampling was used to test 2 hypotheses: that the northern Andes have been disconnected in the past and connected by rapid but repeated eruptions of caldera-forming eruptions in the Colombian Massif fostering episodic dispersal, or alternatively, that they have always been continuous and have gradually uplifted hosting continuous diversification and dispersal through time. In broadly this same area, genetic and phenotypic data revealed the existence of a hybrid zone between species in the warbler genus Myioborus. Because hybridization is likely younger than volcanic activity, topographic connection spurred by volcanism could have also enabled secondary contact between previously isolated species, a hypothesis that merits formal testing. Altogether, we emphasize the pertinence of the volcanic record in offering opportunities for the evaluation of biogeographical hypotheses in the context of Neotropical mountains and their singularly outsized biodiversity.

Species richness, body size, and range size are among key subjects in animal macroecology and biogeography. To date, the species richness–body size–range size nexus remains largely understudied at a global scale and for large taxonomic groups. Here we examine the relative role of species richness and body size in determining species range size among terrestrial vertebrates across spatial and taxonomic scales. We then test related hypotheses in the context of Rapoport’s rule, latitude, and climate variation. To do this, we used simultaneous autoregressive analysis and structural equation modeling to test for statistical relationships among species richness, body size, and range size for all terrestrial vertebrates and for each continent. We then investigated the relative contributions of richness, body size, latitude, climate variation, and their combinations in the variations in species range sizes. We found that species richness consistently shows strong negative correlations with range size at global, regional, and within-region levels, and for all terrestrial vertebrates, and for each of the four classes (i.e., birds, mammals, amphibians, and reptiles). The strength of the relationships increased with richness and with spatial and taxonomic scales. Globally, species richness explained more variation in species range size than did latitude and climates. Body size contributed significantly to the range sizes of all four classes but especially reptiles and amphibians. However, the relative contributions of these factors varied substantially among the continents and terrestrial vertebrate classes. Comparison with the findings of a previous study shows that there were also significant differences in regional patterns between terrestrial vertebrates and plants and the relative contributions of diversity vs. latitude. Our findings show clear relationships among species richness, body size, and range size, but the strength of the relationships varies among regions and taxonomic groups. In general, species richness could predict species range size better than body size, latitude, and climate. These results have important theoretical and applied implications.

Trait measures are affected by intra- and interspecific variability. Most studies aggregate species-level data to averages to analyze patterns of interspecific variation. Reliable per-species averages require data for many individuals per species, which leads to insurmountable measuring effort when studying species-rich assemblages. Here we argue that across a large number of species, patterns and relationships can be precisely recovered even if they are based on measures from a single individual per species. While these deviate to an unknown degree from the true per-species averages, randomly distributed errors will level out across many species. We used subsamples of body size data along elevational gradients for moths and small mammals (dozens to several hundred species per dataset), as well as simulated species assemblages, to illustrate this effect and explore some of its consequences. Single-individual measures correlated well with “true” (i.e., full data) averages. Furthermore, single-individual measures recovered the same conclusions on elevation-body size relationships as true data. Randomly removing individuals per species recovered true elevation-body size relationships very well, while randomly dropping species quickly led to high random variability in relationships across subsampling runs. Simulated species assemblages illustrated how the ratio of intraspecific to interspecific variability affects the correlation between singleton-based and true data. We conclude that trait measures based on single individuals are a viable alternative to multi-individual averages when analyzing assemblages of medium to high species richness. Reducing study effort by limiting the measurement of individuals per species, while retaining all species, is a much more reliable approach than restricting the number of species included in a study.

We tested the hypothesis that, for land snails, long-distance dispersal across oceans is primarily via aerial dispersal (i.e. wind- or bird-mediated), which likely favors so-called micromolluscs through immigrant selection for small (aerially buoyant) body size. Immigrant selection is a filtering process favoring phenotypes conferring greater capacities for long-distance dispersal. We also tested predictions of E. O. Wilson’s taxon cycle, which hypothesizes that descendant species of island colonists are subject to a series of ecological and evolutionary dynamics, resulting over time in progressively more ecologically specialized island endemics with more limited dispersal capacity. We tested predictions of immigrant selection on aerial dispersal and the taxon cycle in native Pacific Island land snails of the Samoan Islands, Mariana Islands, and Lord Howe Island and neighboring small islands using geographic range, shell size, microhabitat, and elevation data compiled from primary and secondary literature. Single-archipelago endemic species found on multiple islands within an archipelago had significantly larger shell sizes than widespread species found in multiple archipelagos and single-island endemic species. Single-archipelago endemic and single-island endemic species were associated with vegetation and ground/rock microhabitats, respectively, whereas widespread species were more likely to be microhabitat generalists. Single-island endemic species were more likely to occur at high-elevation habitats, while widespread species were more likely to be confined to low-elevation habitats. Consistent with predictions of the taxon cycle and immigrant selection on aerial dispersal, Pacific Island land snails endemic to single islands or archipelagos (i.e. those assumed to be later in the taxon cycle) are more likely to have larger body size (archipelago endemics) and to occupy higher elevations (i.e. island interiors; island endemics) in more specialized microhabitats (all endemics).

The ecosystem services and immense biodiversity of Amazon rainforests are threatened by deforestation and forest degradation. A key goal of modern archaeology and paleoecology in Amazonia is to establish the extent and duration of past forest disturbance by humans. Fossil phytoliths are an established proxy to identify the duration of disturbance in lake sedimentary and soil archives. What is not known, is the spatial scale of such forest disturbances when identified by phytoliths. Here we use phytolith assemblages to detect local-scale forest openings, provide an estimate of extent, and consider long-term forest recovery. We use modern phytolith assemblages of 50 Amazonian lakes to i) assess how phytolith assemblages vary across forest cover at 5 spatial scales (100 m, 200 m, 500 m, 1 km, 2 km), ii) model which phytolith morphotypes can accurately predict forest cover at 5 spatial scales, and iii) compare phytoliths with pollen to quantify their relative ability to detect forest cover changes. DCA results show phytolith assemblages could be used to differentiate low, intermediate, and high forest cover values, but not to distinguish between biogeographical gradients across Amazonia. Beta regression models show Poaceae phytoliths can accurately predict forest cover within 200 m of Amazonian lakes. This modern calibration dataset can be used to make quantitative reconstructions of forest cover changes in Amazonia, to generate novel insights into long-term forest recovery. Combining phytoliths and pollen provides a unique opportunity to make qualitative and quantitative reconstructions of past vegetation changes, to better understand how human activities, environmental and climatic changes have shaped modern Amazonian forests.

Mountain shrublands are widespread habitats of the European Alps. Shrub encroachment into above treeline grazed lands profoundly modifies biodiversity and ecosystem functioning. Yet, mountain shrublands remain overlooked in vegetation distribution modeling because it is difficult to distinguish them from productive grasslands. Here, we used the pigment-sensitive spectral indices based on Sentinel-2 bands within a specific phenological window, to produce a high-resolution distribution map of mountain shrublands in the French Alps. We evaluated the performance of our classification using a large dataset of vegetation plots and found that our model is highly sensitive to Ericaceous species which constitute most of the dense alpine shrublands in the French Alps. Our analysis of topoclimatic and land use factors limiting the shrubland distribution at regional scale found that, consistent with the ecophysiology of shrubs, expansion is limited by a combination of water deficit and temperature. We discussed the past and current land-use implications in the observed distribution and put forward hypotheses combining climate and land-use trajectories. Our work provides a baseline for monitoring mountain shrub dynamics and exploring the response of shrublands to past and ongoing climate and land use changes.