COS 132-1
Biodiversity, productivity, and the spatial insurance hypothesis revisited
Accelerating rates of biodiversity loss have led ecologists to explore the effects of species richness on ecosystem functioning and the flow of ecosystem services. One explanation of the relationship between biodiversity and ecosystem functioning lies in the spatial insurance hypothesis, which centers on the idea that productivity and stability increase with biodiversity in a temporally varying, spatially heterogeneous environment. The greater the number of spatially distributed species, the greater the functional redundancy of species at particular locations, and the more the system is protected against spatial environmental variability including spatially distributed anthropogenic shocks.
In a pivotal theoretical framework, Loreau et al.(2003) developed and corroborated this hypothesis. However, there has been little work on the impact of dispersal where environmental risks are more or less spatially corroborated, or where dispersal rates are variable. In this study, we re-evaluate the original Loreau model and extend it to consider stochastic temporal variation in resource availability, which we refer to as "environmental risk," and heterogeneity in dispersal rates.
Results/Conclusions
Our central finding is that the stabilizing effect of dispersal is more robust to local risk factors than to global risk factors. We find that asynchronies across communities and species provide community-level stabilizing effects on productivity, despite varying levels of species richness. Although intermediate dispersal rates play a role in mitigating environmental risk, they are much less effective in insuring productivity against global (metacommunity-level) than local (individual community-level) risks.
Communities and ecosystems have become both more connected worldwide and more exposed to global risk events. Anthropogenic dispersal of species through trade and travel has led to the significantly higher dispersal rates and the homogenization of many ecosystems, with consequences for both biodiversity and productivity. At the same time, the increasing connectivity of ecosystems as a result of globalization has affected the spatial distribution of environmental risk. Given the potentially irreversible consequences of high dispersal rates in these circumstances it may be useful to have a sense of the tradeoff between dispersal, biodiversity, productivity and the spatial correlation of risk in real systems. From a policy or management perspective, this may be critically important when deciding whether to invest in adaptation to or mitigation of environmental change.
Loreau, M., Mouquet, N., Gonzalez, A. 2003. Biodiversity as spatial insurance in heterogeneous landscapes. PNAS. 100(22):12765-12770.