Contrasted responses of orchid occurrence between community and species level to the vegetation dynamics in Mediterranean region: first lessons from a 30 year long sampling interval using a Site-Occupancy Model
Résumé
There is an increasing interest in understanding and evaluating shifts in biodiversity induced by the ongoing global change. Orchids are particularly relevant organisms to investigate diachronic variations because they respond to anthropic pressure (land-use change, habitat fragmentation, etc.). Here we used a Site-Occupancy Model in order to describe the dynamics of orchid occurrence in Corsica at community and species level, and evaluate the influence of land-use change on orchid occurrence. We compared the occurrence of 45 orchid species at 62 locations in Corsica between 1982?1984 and 2009?2011. Data were collected by the same observer during the two sampling periods applying the same protocol of species inventories. We considered environmental factors and species biological traits as co-factors in the Site-Occupancy Model to estimate the probability of species detection. At community level, we found no significant difference in orchid occurrence between the two sampling periods, in contrast to the species level. Species responded differently to the increase of vegetation cover. We concluded that (i) conservation strategies should be species-dependent, as we observed contrasted responses to the land-use change between species, and (ii) that the use of Site-Occupancy Models is an appropriate way to analyze temporal dynamics of orchids and to investigate the ecological processes underlying these dynamics.