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There is still considerable debate about which mechanisms drive the relationship between biodiversity and ecosystem function (BEF). Although most scientists agree on the existence of two underlying mechanisms, complementarity and selection, experimental studies keep producing contrasting results on the relative contributions of the two effects. We present a spatially explicit resource competition model and investigate how the strength of these effects is influenced by trait and environmental variability, resource distribution, and species pool size. Our results demonstrate that the increase of biomass production with increasing species numbers depends on the concurrence of environmental and trait variability: BEF relationships are stronger if functionally different species coexist in a landscape with heterogeneous resource supply. These large biodiversity effects arise from complementarity effects, whereas selection effects are maximized when broad trait ranges coincide with narrow ranges of resource supply ratios. Our results will therefore help to resolve the debate on complementarity and selection mechanisms. [ABSTRACT FROM AUTHOR]

Ecological communities are often characterised by many species occupying the same trophic level and competing over a small number of vital resources. The mechanisms maintaining high biodiversity in such systems are still poorly understood. Here, we revisit the role of prey selectivity by generalist predators in promoting biodiversity. We consider a generic tri-trophic food web, consisting of a single limiting resource, a large number of primary producers and a generalist predator. We suggest a framework to describe the predator functional response, combining food selectivity for distinctly different functional prey groups with proportion-based consumption of similar prey species. Our simulations reveal that intermediate levels of prey selectivity can explain a high species richness, functional biodiversity, and variability among prey species. In contrast, perfect food selectivity or purely proportion-based food consumption leads to a collapse of prey functional biodiversity. Our results are in agreement with empirical phytoplankton rank-abundance curves in lakes. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms driving species biogeography and biodiversity remains a major challenge in phytoplankton ecology. Using a model of two phytoplankton species with a gleaner-opportunist trade-off and competing for light and a limiting nutrient, we show that the diel light cycle may be an essential factor to explain large-scale ecological patterns. When only the seasonal light cycle is considered (control scenario) the model predicts that, independently of the nutrient supply, gleaners should dominate across all latitudes and opportunists can obtain a temporal niche only at high latitudes. However, the diel light cycle makes the competition outcome also a function of nutrient supply by affecting the amplitude of diel nutrient oscillations, with gleaners dominating when nutrient supply is low, opportunists when nutrient supply is high, and both species coexisting at intermediate levels of nutrient supply. The combined effects of seasonal and diel light cycles (diel scenario) shape a latitudinal diversity gradient with decreasing diversity towards higher latitudes and a unimodal dependence of diversity on nutrient supply and, therefore, on ecosystem productivity. The proposed mechanism can help interpret the biogeography of major phytoplankton functional groups in the global ocean and link them with large-scale biodiversity patterns. [ABSTRACT FROM AUTHOR]