Does disturbance drive the collapse of biotic interactions at the severe end of a diversity–biomass gradient?
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It has been recently proposed that the decrease in diversity towards the severe end of the humped-back diversity–biomass model of Grime was driven by a collapse of facilitation due to extreme conditions of either stress or physical disturbance. In order to test the hypothesis that disturbance is the primary direct factor driving the collapse of interactions occurring along environmental severity gradients, we conducted a removal experiment in the highly stressed French coastal dunes along a gradient of disturbance due to sand burial. Four dune species were used as targets and transplanted with and without neighbours in four communities along the gradient. The experiment was conducted twice, a dry and an average year. Results of the experiment showed that during the dry year the effect of the environment was prominent and only one species was facilitated for survival in the least disturbed community. During the average year, interactions for growth were important only in the same community, with positive or negative responses depending on the natural position of the target species within the coastal dune gradient. In accordance with our hypothesis, most interactions for both survival and growth were observed in the least disturbed community exhibiting the highest diversity. There were no interactions in the most disturbed community with the lowest diversity.
KeywordsCoastal sand dunes Competition Facilitation Physical disturbance Stress
This research was funded by the “Région Aquitaine”. We are grateful to the “Office National des Forêts” (O·N.F.) for permission to work in public coastal sand dunes. We sincerely thank Jean Laporte-Cru, Annie Laporte-Cru, Priscillia Trouillard, Laurène Claudel, David Rosebery, David Richin, and Bénédicte Roux for their help in the field during the experiment. We also thank Sylvain Delzon for statistical and methodology advices and Lohengrin Cavieres, Yoann Le Bagousse-Pinguet and Sabrina Sérac for their comments on this manuscript.
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