Rafael Molina-Venegas

Disentangling environmental correlates of vascular plant biodiversity in a Mediterranean hotspot

We determined the environmental correlates of vascular plant biodiversity in the Baetic-Rifan region, a plant biodiversity hotspot in the western Mediterranean. A catalog of the whole flora of Andalusia and northern Morocco, the region that includes most of the Baetic-Rifan complex, was compiled using recent comprehensive floristic catalogs. Hierarchical cluster analysis (HCA) and detrended correspondence analysis (DCA) of the different ecoregions of Andalusia and northern Morocco were conducted to determine their floristic affinities. Diversity patterns were studied further by focusing on regional endemic taxa. Endemic and nonendemic alpha diversities were regressed to several environmental variables. Finally, semi-partial regressions on distance matrices were conducted to extract the respective contributions of climatic, altitudinal, lithological, and geographical distance matrices to beta diversity in endemic and nonendemic taxa. We found that West Rifan plant assemblages had more similarities with Andalusian ecoregions than with other nearby northern Morocco ecoregions. The endemic alpha diversity was explained relatively well by the environmental variables related to summer drought and extreme temperature values. Of all the variables, geographical distance contributed by far the most to spatial turnover in species diversity in the Baetic-Rifan hotspot. In the Baetic range, elevation was the most significant driver of nonendemic species beta diversity, while lithology and elevation were the main drivers of endemic beta diversity. Despite the fact that Andalusia and northern Morocco are presently separated by the Atlantic Ocean and the Mediterranean Sea, the Baetic and Rifan mountain ranges have many floristic similarities – especially in their western ranges – due to past migration of species across the Strait of Gibraltar. Climatic variables could be shaping the spatial distribution of endemic species richness throughout the Baetic-Rifan hotspot. Determinants of spatial turnover in biodiversity in the Baetic-Rifan hotspot vary in importance between endemic and nonendemic species.

Climatic and topographical correlates of plant palaeo- and neoendemism in a Mediterranean biodiversity hotspot

Background and Aims Understanding the evolutionary and ecological forces contributing to the emergence of biodiversity hotspots is of outstanding importance to elucidate how they may withstand current climate changes. Here we explored patterns of phylogenetic and non-phylogenetic plant endemism in a Mediterranean biodiversity hotspot. We hypothesized that areas with wet and equable climatic conditions would be prone to long-term persistence of endemic lineages (palaeoendemism), whilst areas of recent local speciation (neoendemism) would be more related to harsher environmental conditions and to high topographical relief promoting speciation. Methods We focused on the Baetic–Rifan biodiversity hotspot (southern Iberian Peninsula and northern Morocco) in combination with molecular phylogenetic information and relative phylogenetic endemism (RPE), a recent phylogenetic measure of endemism, allowing us to discern centres of palaeo- from those of neoendemism. Using eco-geographical regions as study units, we explored correlations between both RPE and endemic species richness with precipitation- and temperature-related variables and with elevation range. Key Results Centres of neoendemism were concentrated towards the easternmost part of the hotspot, while centres of palaeoendemism were clustered in the vicinity of the Strait of Gibraltar. The RPE index, indicating more palaeoendemism, was positively correlated with total annual precipitation, while endemic species richness showed a poor correlation. In contrast, elevation range and mean annual temperature were poor predictors of RPE, despite elevation range showing a strong correlation with endemic species richness. Conclusions The Baetic–Rifan biodiversity hotspot shows clearly differentiated centres of neo- and palaeoendemism. Topographical relief may have driven evolutionary diversification of newly evolved species, while water availability seems more critical for the long-term persistence of ancient lineages in refuge areas of smoother topography. Given climatic trends towards increasing aridification, conservation planners should pay particular attention to preserve areas retaining older phylogenetic lineages, as these areas act as ‘natural museums’ of biodiversity within the Baetic–Rifan biodiversity hotspot.

The building of a biodiversity hotspot across a land-bridge in the Mediterranean.

Many of the macroevolutionary processes that have shaped present-day phylogenetic patterns were caused by geological events such as plate tectonics and temporary land-bridges. The study of spatial patterns of phylogenetic diversity can provide insights into these past events. Here we focus on a western Mediterranean biodiversity hotspot located in the southern Iberian Peninsula and northwest Africa, two regions that are separated by the Strait of Gibraltar. We explore the spatial structure of the phylogenetic relationships within and across large-scale plant assemblages. Significant turnover in terminal lineages tends to occur between landmasses, whereas turnover in deep lineages tends to occur within landmasses. Plant assemblages in the western ecoregions of this hotspot tend to be phylogenetically overdispersed but are phylogenetically clustered on its eastern margins. We discuss our results in the light of potential scenarios of niche evolution (or conservatism) and lineage diversification. The significant turnover between landmasses suggests a common scenario of allopatric speciation that could have been facilitated by the intermittent joining of the two continents. This may have constituted an important stimulus for diversification and the emergence of this western Mediterranean biodiversity hotspot.

How soil and elevation shape local plant biodiversity in a Mediterranean hotspot

Elucidating how evolutionary and ecological factors drive the assemblage of communities in biodiversity hotspots remains an important challenge. This currently impedes our ability to predict the responses of communities to the ongoing global changes in these major world’s biodiversity reservoirs. Here, we focus on the Sierra Nevada mountain range, a core region of the Baetic-Rifan biodiversity hotspot in the western Mediterranean, and explore the relative importance of soil properties and elevation in shaping phylogenetic and functional diversity of shrub communities. We recorded the total number of each species in community transects across elevation gradients and contrasting soil conditions, and measured some ecologically relevant functional traits (specific leaf area, leaf carbon:nitrogen ratio, plant height and blooming duration). Phylogenetic distances among species were inferred from a genus-level time-calibrated molecular phylogeny. Elevation was the main factor predicting phylogenetic and functional alpha diversity of plant communities. Species in high-elevation communities were phylogenetically distant but functionally similar, being relatively smaller and having relatively short blooming durations, whilst species in low-elevation communities showed the opposite pattern. Beta diversity in SLA and leaf C:N ratio based on species incidences were positively correlated with a soil pH and micronutrient gradient. Specifically, communities that develop on soils of high pH and low micronutrient concentrations showed low SLA values and high leaf C:N ratios, whilst communities on soils of lower pH and high micronutrient concentrations showed the opposite pattern. We conclude that soil properties and elevation simultaneously shape the structure of Mediterranean shrub communities by differentially acting on the different dimensions of the species niches. Elevation seems to filter plant height and phenology-related traits whereas nutrient-related functional traits are more related to soil properties. Our study illustrates the primary role of environmental heterogeneity for the maintenance of diversity in Mediterranean mountain ecosystems.

Using floristics, modern systematics and phylogenetics for disentangling biodiversity hotspots across scales: a Mediterranean case study

Abstract Biodiversity comprises various levels of biological organisation. Global patterns of biodiversity are well established based on species occurrence. However, functional and historical processes underlying biodiversity patterns have been only recently approached. The increasingly active field of phylogenetics has allowed the rise of phylofloristic studies to help in elucidating the historical, evolutionary causes of plant biodiversity in addition to most commonly approached ecological correlates. Here, we review recent phylogeny-based studies disentangling the role of eco-geographic and historical factors on the biodiversity patterns of the Baetic–Rifan range and exemplify the use of barcoding to explore the evolutionary assembly of woody flora in the Spanish Sierra Nevada mountain range super-hotspot. Our species-level DNA barcoding approach resulted in a phylogeny potentially improving refinement of hypotheses in comparison with previous approaches based on phylogenies at genus level, and providing insights into the woody flora of Sierra Nevada subjected to systematic discussion. We show that the roles of elevation and substrate in biodiversity distribution vary according to the biodiversity component considered and also between endemic and non-endemic flora. We aim to illustrate how modern methods can further our understanding of the mechanisms underlying the assemblage of species and, consequently, the conservation of biodiversity.

Evolutionary history predicts the response of tree species to forest loss: A case study in peninsular Spain

Evolutionary history can explain species resemblance to a large extent. Thus, if closely related species share combinations of traits that modulate their response to environmental changes, then phylogeny could predict species sensitivity to novel stressors such as increased levels of deforestation. To test this hypothesis, we used 66,949 plots (25-m-radius) of the Spanish National Forest Inventory and modelled the relationships between local (plot-level) stem density of 61 Holarctic tree species and forest canopy cover measured at local and landscape scales (concentric circles centred on the plots with radiuses of 1.6, 3.2 and 6.4 km, respectively). Then, we used the output model equations to estimate the probability of occurrence of the species as a function of forest canopy cover (i.e. response to forest loss), and quantified the phylogenetic signal in their responses using a molecular phylogeny. Most species showed a lower probability of occurrence when forest canopy cover in the plots (local scale) was low. However, the probability of occurrence of many species increased when forest canopy cover decreased across landscape scales. We detected a strong phylogenetic signal in species response to forest loss at local and small landscape (1.6 km) scales. However, phylogenetic signal was weak and non-significant at intermediate (3.2 km) and large (6.4 km) landscape scales. Our results suggest that phylogenetic information could be used to prioritize forested areas for conservation, since evolutionary history may largely determine species response to forest loss. As such, phylogenetically diverse forests might ensure contrasted responses to deforestation, and thus less abrupt reductions in the abundances of the constituent species.