Species densities, biological interactions and benthic ecosystem functioning: an in situ experiment

摘要

Understanding how biota affect the functioning of ecosystems is imperative if we are to predict the impacts of ongoing biodiversity change on ecosystem service provision. Evidence from marine sediments-the most widespread habitat on earth-suggests that ecological function delivery is driven by the presence and densities of certain species. However, most experiments have been conducted using fixed density treatments and run for short durations (<4 wk) within homogenous laboratory microcosms. In nature, the impact of changing density in one species may depend on consequent changes in the densities of others. Moreover, evidence from vegetation assemblages suggests that the influence of complementarity among species increases in heterogeneous environments and over time. Here, we simulated a realistic pattern of biodiversity change by transplanting the macroinfaunal bivalve Scrobicularia plana into an intertidal mudflat at various densities. The impact on redox potential discontinuity (RPD) depth (a proxy for benthic functioning) was measured at 1, 5 and 9 wk. Increasing S. plana density negatively affected RPD depth (i.e. RPD depth became shallower) by causing the density of a functionally dominant species, Corophium volutator, to decline. Furthermore, the influence of density-dependent interspecific interactions (among macroinfauna) on RPD depth became increasingly positive as the experiment progressed. Our results reaffirm the direct functional importance of certain species in a natural ecosystem and highlight the indirect importance of other species to which their density is tightly coupled. An implication is that species loss could enhance functioning if it causes the density of a functionally dominant species to increase. Nevertheless, the apparent temporal emergence of interspecific facilitation suggests that diverse species assemblages promote high function delivery.