Biodiversity as spatial insurance in heterogeneous landscapes

Abstract

The potential consequences of biodiversity loss for ecosystem functioning and services at local scales have received considerable attention during the last decade, but little is known about how biodiversity affects ecosystem processes and stability at larger spatial scales. We propose that biodiversity provides spatial insurance for ecosystem functioning by virtue of spatial exchanges among local systems in heterogeneous landscapes. We explore this hypothesis by using a simple theoretical metacommunity model with explicit local consumer-resource dynamics and dispersal among systems. Our model shows that variation in dispersal rate affects the temporal mean and variability of ecosystem productivity strongly and nonmonotonically through two mechanisms: spatial averaging by the intermediate-type species that tends to dominate the landscape at high dispersal rates, and functional compensations between species that are made possible by the maintenance of species diversity. The spatial insurance effects of species diversity are highest at the intermediate dispersal rates that maximize local diversity. These results have profound implications for conservation and management. Knowledge of spatial processes across ecosystems is critical to predict the effects of landscape changes on both biodiversity and ecosystem functioning and services.T he potential consequences of biodiversity loss for ecosystem functioning and services have received considerable attention during the last decade (1-3). Several controlled experiments have now established that species diversity influences ecosystemlevel processes such as primary production in grasslands (4-7) and heterotrophic consumption of suspended resources in streams (8). These experiments, however, have typically been performed over small spatial and temporal scales relative to the size and generation time of the organisms involved. At these small scales, uncontroversial effects of biodiversity due to functional complementarity among species with different traits have been shown only at low to moderate levels of diversity (1).It is possible that the functional significance of biodiversity will fully appear only at larger spatial and temporal scales. The insurance hypothesis (9) proposes that species or phenotypes that are functionally redundant for an ecosystem process at a given time may show temporal complementarity because of asynchronous responses to environmental fluctuations. In this case, biodiversity acts as insurance for ecosystem functioning against temporal environmental change because functional compensations among types provide enhanced and more predictable aggregate ecosystem properties. A number of theoretical studies have provided support for this hypothesis (9-15) although experimental evidence remains scanty and controversial (reviewed in ref. 16). Similarly, species or phenotypes may complement each other in space, such that a more diverse species pool allows better occupation of spatial gradients (17).This theoretical work has usually not considered explicitl...

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