BIODIVERSITY MEDIATES PRODUCTIVITY THROUGH DIFFERENT MECHANISMS AT ADJACENT TROPHIC LEVELS.pdf

Ecology, 88(11), 2007, pp. 2821–2829  2007 by the Ecological Society of America BIODIVERSITY MEDIATES PRODUCTIVITY THROUGH DIFFERENT MECHANISMS AT ADJACENT TROPHIC LEVELS ZACHARY T. LONG,1,2,4 JOHN F. BRUNO,3 AND J. EMMETT DUFFY2 1Institute of Marine Sciences, The University of North Carolina, Chapel Hill, Morehead City, North Carolina 28557 USA 2School of Marine Sciences, The College of William and Mary, Gloucester Point, Virginia 23062-1346 USA 3Department of Marine Sciences, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3300 USA Abstract. Biodiversity may enhance productivity either because diverse communities more often contain productive species (selection effects) or because they show greater complementarity in resource use. Our understanding of how these effects influence community production comes almost entirely from studies of plants. To test whether previous results apply to higher trophic levels, we first used simulations to derive expected contributions of selection and complementarity to production in competitive assemblages defined by either neutral interactions, dominance, or a trade-off between growth and competitive ability. The three types of simulated assemblages exhibited distinct interaction signatures when diversity effects were partitioned into selection and complementarity components. We then compared these signatures to those of experimental marine communities. Diversity influenced production in fundamentally different ways in assemblages of macroalgae, characterized by growth– competition trade-offs, vs. in herbivores, characterized by dominance. Forecasting the effects of changing biodiversity in multitrophic ecosystems will require recognizing that the mechanism by which diversity influences functioning can vary among trophic levels in the same food web. Key words: biodiversity; complementarity effect; ecosystem functioning; food web; selection effect; tripartite partition. INTRODUCTION The potential