Biomass–Diversity Responses and Spatial Dependencies in Disturbed Tallgrass Prairies

Abstract

Monotonic, hump-shaped and zero-correlation productivity-diversity relationships have been found to date in many ecosystems. This diversity of responses has puzzled ecologists in their search for general principles on ecosystem functioning. Some state that the scale of observation is crucial in defining this relationship. We have developed a spatial model of tallgrass prairies where biomass and litter dynamics are defined by uncoupled difference equations. In this system, we periodically apply prescribed fire as a disturbance that propagates through neighboring cells. The model shows percolation thresholds at points where small-scale spatial heterogeneity and large-scale, global correlation coexist, resulting in power-law distributions in available areas for non-dominant species. These points maximize the biomass-diversity relationship. Our results suggest that spatial dependencies and the disturbance heterogeneity hypothesis are the cornerstone processes accounting for unimodality in productivity-diversity relationships.

Gap percolation in rainforests

“…When sets of neighbouring, connected small‐scale sites define a cluster spanning the entire system under consideration, such cluster is called a percolation cluster (Stauffer and Aharony 1985, Peitgen et al 1992, Milne et al 1996, Keitt et al 1997). Percolation phenomena influence metapopulation dynamics (Andren 1994, Bascompte and Solé 1996, Wiens et al 1997, With and King 1999), invasion processes (Loehle et al 1996, With 2002), and are relevant to conservation biology (With 1997, Bunn et al 2000) and ecosystem function (Gamarra and Solé 2002).…”