Biodiversity mediates temporal sensitivity of ecosystems to climate variability

Brunno F. Oliveira, Environmental Science and Policy, University of California Davis, Davis, CA and Xiaoli Dong, Environmental Science and Policy, University of California, Davis, Davis, CA

Background/Question/Methods
Ecosystem processes vary through time in response to environmental fluctuations and disturbances. The sensitivity of ecosystems to such external forces is a key component of resilience. Accumulating evidence indicates that biodiversity can reduce ecosystem sensitivity (enhance resilience). This effect has been attributed to complementarity in resource consumption, reduced density-dependent herbivore and pathogen pressure, facilitation, or higher chance that productive species are present at the community. Although a positive biodiversity effect on ecosystem resilience relationship is the most common pattern, variation in the strength and shape of this relationship along environmental gradients has led to debates about the generality of these patterns and their casual mechanisms. Yet, previous studies on this topic typically used isolated ground-based observations or experimental manipulations over relatively short spatial and temporal scales.
Here, we investigate (1) whether biodiversity affects sensitivity of ecosystems to temperature and precipitation, and (2) how the strength of this effect changes along aridity gradients across the entire Western Hemisphere. To do so, we combine plant biodiversity data and satellite-based proxies of ecosystem primary productivity (EVI) and climate conditions (temperature, precipitation and aridity). We estimate three dimensions of plant biodiversity—species richness, phylogenetic diversity and functional diversity, using data from BIEN. First, using times series of 20-year monthly averaged values, we quantify the sensitivity of EVI to precipitation and temperature. We then fitted spatial models to evaluate (1) whether the three dimensions of biodiversity affect ecosystem sensitivity and (2) how the effect changes along the aridity gradient.

Results/Conclusions
We found that biodiversity decreases sensitivity to temperature, but increases sensitivity to precipitation. When looking at these effects along a gradient of increasing aridity, we identified an erosion of biodiversity effects on both ecosystem sensitivity to temperature and precipitation. In contrast, towards more humid regions, biodiversity reduces sensitivity to temperature while increases sensitivity to precipitation. This reveals a mediating effect of aridity in a trade-off that determines whether biodiversity benefits ecosystem sensitivity to thermal vs hydric stress.