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Functional mechanisms of community assembly in semi-arid Mediterranean shrublands

2011Functional mechanisms of community assembly in semi-arid Mediterranean shrublands.SORIANO MORALES Sara Isabel (Mexico)
Organisation:University of Poitiers, Poitiers (FR)Supervisor :
Summary: Plant functional traits vary along environmental gradients: both between and within communities. Community assembly theory suggests two processes driving trait distribution between communities: habitat filtering (HF) and niche differentiation (ND). Within communities, biotic interactions impact the spatial distributions of plants and determine community response to environmental changes. We quantify trait distribution patterns along an aridity gradient in Spanish Mediterranean shrublands with a multi-scale analysis. Vegetation structure and biotic interactions have been proposed as key factor determining this ecosystem response to global desertification. Using a null model approach, we show that functional structure in Spanish shrublands results of deterministic processes. Both HF and ND were find determining community structure. Within communities, an original methodology is proposed based on community traits spatial distribution and neighborhood trait distribution to detect the effect of biotic interactions as a structuring force. Contrary with previous studies, we found that at community scale, trait spatial organization is drive by competition while at local scale, facilitation determined the species coexistence. Non-linear vegetation changes might be product of facilitation collapse at community level, occurring twice along the aridity gradient. This study is the first step in the comprehension of the response and effect of semi-arid ecosystems toward the global change.