Comprehending the mechanisms that drive spatial-temporal variation in biological diversity is at the core of ecological inquiry. How species distribution and abundance vary in space is strongly related to “natural” environmental gradients, in which the diversity of site characteristics allow the establishment and persistence of different sets of species. However, the current fast pace of natural habitat conversion is leading to a spatial-temporal reorganization of species distributions and to high levels of biodiversity loss. Moreover, species are being transported and released outside of their native ranges at unprecedented rates, making it imperative to ecologists to understand how ecological communities and ecosystems respond to species introductions. Thus, discriminating the relative role of environmental and anthropocentric factors as drivers of native and non-native biodiversity patterns is important not only for understanding the fundamental processes that shape species diversity dynamics across heterogeneous landscapes, but also for developing sound conservation policies capable to mitigate biodiversity loss.
In a recent published contribution led by Rodrigo S. Bergamin, we investigated how environmental and anthropogenic drivers affect native and alien plant species in the Rio de la Plata Grasslands.
The Río de La Plata Grassland Bioregion
The Río de la Plata grassland region (RPG) is one of the largest extensions of temperate grassland ecosystems in the world. Located in the Southern America realm, the RPG extends across an estimated area of 111 million hectares, from the drylands east of the Andes to the Atlantic Ocean, and it contains five ecoregions: Uruguayan Savanna, Espinal, Humid Pampas, Paraná Flooded Savanna, Southern Cone Mesopotamian Savanna. This vast and heterogeneous open-vegetation ecosystem harbours not only grasslands and savannas but also a myriad of wetlands and riverine and coastal ecosystems and forests, being home to at least 4,904 vascular plant species, of which about 8% are endemic to the RPG and more than 10% are allochthonous (see for also Andrade et al. 2018). Despite its great diversity and extensive natural landscapes, in the past years the RPG has become one of the regions of the world with the highest rates of change in land cover and use; Cropland, planted pastures and afforestation have replaced RPG’s natural ecosystems at alarming rates (Baeza & Paruelo 2020).
Patterns of alien and native grassland diversity across scales
To examine the role of environmental and anthropogenic drivers in shaping components of grassland diversity across different spatial scales, we compiled a large-scale data set of vascular plant communities in remnants of native grasslands in the RPG. Based on this data we partitioned both native and alien plant species diversity into two spatial components: alpha diversity ( i.e., diversity within an ecological community) and beta-diversity (i.e., changes in species composition among ecological communities). We then investigated how environmental and anthropogenic variables affected these two spatial components of ecological diversity.
We found that native species richness is still highly shaped by “natural gradients”, while alien species richness is shaped by both natural environmental and anthropogenic factors. Species diversity for native species is higher in sites with less demanding environmental conditions, whereas the number of alien species increases in more alkaline soils, and with cropland density and road density. Both environmental and anthropogenic factors affected native and alien beta-diversity, with areas within a similar geographical context sharing more taxonomically similar assemblages. Compositional dissimilarity of alien plants decreased with increasing road density, which means that road encroachment homogenizes communities due to the presence of introduced species.
Our results shed light on the processes shaping diversity patterns in the RPG, and they stress that in this grassy ecosystem the richness of native plants is still mainly shaped by environmental factors, while natural and anthropogenic factors shape alien species diversity and distribution.
To find out more, read our new paper “Native and alien grassland diversity respond differently to environmental and anthropogenic drivers across spatial scales” just published in the Journal of Vegetation Science.
Geekcologist 