Climate change is altering natural ecosystems in diverse ways. Shifts in species ranges and biological invasions are two of the most consequential of these impacts. These processes are associated with regional reductions in biodiversity, altered ecosystem function and reorganized species interactions. Yet for species-rich Mediterranean ecosystems, there is little experimental data on how communities will respond to climate change. We use these data to better our understanding of how and whether annual plant species (be they from a neighboring region or exotics) will invade natural plant communities under climate change scenarios.
Taking advantage of a strong precipitation gradient present in Israel, we worked at two sites, representing Mediterranean and semi-arid climates. At each site, we manipulated rainfall by using rainout shelters to simulate predicted drought in the middle of the century. Across a range of microsites at both sites, and at two precipitation treatments (drought and natural rainfall), we have assessed the success of planted invaders (both neighboring region and exotic species) relative to each other, to planted natives, and to the surrounding native community.
We determine that habitat heterogeneity and year to year variation are important factors contributing to the ability of species to survive in semi-arid and Mediterranean ecosystems. In particular, the range of variability in abiotic conditions (soil temperature, soil moisture, etc) is large and may well serve to maintain diversity under climate variability. We propose that annual plants integrate over a relatively small physical area and that this may serve to buffer them from changes in average precipitation. We also compare our experimental results to a bioclimatic approach and determine that while there is some overlap for some species, experimental data is better suited to quantify the complexity of future trends.