Introduction: What conservation problem or question does your study address?Semi-arid systems exhibit striking, scale-free patchiness in vegetation. Recent studies have shown that, these patterns can be explained by local facilitative interactions with global competition for resources. However, no alternative explanations have been investigated. Here, we examine whether such patterns could emerge from only local facilitative and local competitive processes and if so, how the involved processes could then be discerned.
Methods: What were the main research methods you used?We compare and contrast the predictions of two spatially explicit models of vegetation patterns. In addition to the afore-mentioned model of global competition and local facilitation (Kéfi S et. al., (2006). Nature 449(7159):213-217), we analyse a model from the literature of non-equilibrium statistical physics in which both, facilitation and competition, occur at local scales (Lübeck S, (2006). Journal of Statistical Physics 123:193). We have considered two forms of this latter model of local competition – with strong and weak facilitation respectively. We compare the realizations of these models with that of a null model with similar density but no interactions (neither competitive nor facilitative).
Results: What are your most important results?We characterize spatial patterns by using the distribution of patch sizes and power spectrum analyses. We find that both models predict a power-law distribution of patch sizes. However, the two models differ in their prediction of characteristics of the power spectrum. Therefore, our results suggest that an analysis of spatial power spectra can be used to distinguish competitive processes occurring at different scales.
Discussion: What are your important discussion points and what is the relevance of your results to conservation (if any)?Semi-arid ecosystems can exhibit characteristic vegetation patterns resulting from varying scales of competitive and facilitative processes. Elucidating the local scale interactions that generate these macroscopic patterns is of fundamental ecological importance. We have demonstrated the validity of two competing explanations for vegetation patterning in semi-arid landscapes and also proposed a means of distinguishing them.