From patches to richness: assessing the potential impact of landscape transformation on biodiversity

Background/Question/Methods

The world is a patchy place.  Natural patchiness and human fragmentation means that habitats are not continuously distributed. We propose a framework to extend the species-area relationship approach and analyze how changes in patches that compose a habitat in a landscape modify the habitat richness. We assume that the communities that inhabit the patches can (1) be affected or unaffected by human activity, (2) have null or unlimited migration and (3) be composed of species that interact neutral- or niche-like. These three criteria define extreme situations of species richness, thus the richness of a real community - with intermediate characteristics- should be contained within the range defined by these extremes. We graphically show how patches make up habitats under present and future conditions, summarizing patch size information and facilitating the interpretation of common fragmentation metrics. Similarly, we propose an index to measure the impact of habitat transformation using the extreme community responses. We use the graph and the index to estimate the impact of (1) current land use change and (2) 2010-2069 climate change scenarios (ensemble of eight climate models for A1B and A2 emission scenarios) on eight biomes of the Tropical Andes.

Results/Conclusions

Using the graph and the index of the framework we find that (1) glacier and cryoturbated areas and paramo grasslands are the most affected biomes by natural patchiness; (2) current land use change affects evergreen montane forest and paramo grasslands more than other biomes; (3) projected climate change impacts are greatest on glacier and cryoturbated areas and paramo grasslands; and (4) the combined effects of land use and projected climate change are also greater for  paramo grasslands and evergreen montane forest. All these biomes are important for water provision and regulation. Dryer biomes are less affected by land use change and have different future trends: Deciduous montane forest has a consistent increase in the expected richness due to climate change, while shrublands, xeric puna grassland and prepuna have uncertain future trends, with mixed results. Finally, the uncertainty due to our lack of knowledge of migratory capability is more important than uncertainties about climate change or human impact. This framework provides a simple and useful approach to understand patchiness effect on biodiversity. Some potential extensions of the model to assess its robustness to continuous migratory capabilities and to other assumptions and simplifications are also discussed.