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Biodiversity and ecosystem functioning (BEF) research advocates that biodiversity loss has a drastic alteration on ecosystem functioning. However, studies have barely investigated how the evolutionary dependence of species traits affects EF. Here, we developed an integrated approach combining functional (FD) and phylogenetic diversity (PD) into a single space to disentangle the effects of diversity on leaf decomposition. We conducted an experiment manipulating plant leaves into litterbags containing four species (from a pool of 27) combined in four different treatments represented by low or high FD and PD; these treatments present different scenarios of trait evolution and, therefore, a treatment with high FD and low PD, for instance, mimics a community assembled by divergent trait evolution of close relatives. We found that leaf decomposition was 30% slower in pools with high FD and PD. We show species pool with higher FD and PD have non-additive effects on decomposition, which means there is a negative effect of mixtures combining species with great functional and evolutionary differences. In addition, interactive effects of PD and FD were more important to leaf decomposition than their isolated effects. Our results suggest that PD and FD have interactive effects on decomposition and represent different axes of ecosystem variation, indicating we should avoid using phylogenies as a proxy for functional diversity. We argue that future BEF experiments may alter their design by considering a multifaceted scenario investigating community effects on ecosystem functioning, and idiosyncratic effects of key traits which may determine community assembly and ecosystem processes. [ABSTRACT FROM AUTHOR]

The enemies hypothesis states that reduced insect herbivory in mixed-species stands can be attributed to more effective top-down control by predators with increasing plant diversity. Although evidence for this mechanism exists for invertebrate predators, studies on avian predation are comparatively rare and have not explicitly tested the effects of diversity at different spatial scales, even though heterogeneity at macro- and micro-scales can influence bird foraging selection. We studied bird predation in an established forest diversity experiment in SW Finland, using artificial larvae installed on birch, alder and pine trees. Effects of tree species diversity and densities on bird predation were tested at two different scales: between plots and within the neighbourhood around focal trees. At the neighbourhood scale, birds preferentially foraged on focal trees surrounded by a higher diversity of neighbours. However, predation rates did not increase with tree species richness at the plot level and were instead negatively affected by tree height variation within the plot. The highest probability of predation was observed on pine, and rates of predation increased with the density of pine regardless of scale. Strong tree species preferences observed may be due to a combination of innate bird species preferences and opportunistic foraging on profitable-looking artificial prey. This study therefore finds partial support for the enemies hypothesis and highlights the importance of spatial scale and focal tree species in modifying trophic interactions between avian predators and insect herbivores in forest ecosystems. [ABSTRACT FROM AUTHOR]

Resource partitioning, facilitation, and sampling effect are the three mechanisms behind the biodiversity effect, which is depicted usually as the effect of plant-species richness on aboveground net primary production. These mechanisms operate simultaneously but their relative importance and interactions are difficult to unravel experimentally. Thus, niche differentiation and facilitation have been lumped together and separated from the sampling effect. Here, we propose three hypotheses about interactions among the three mechanisms and test them using a simulation model. The model simulated water movement through soil and vegetation, and net primary production mimicking the Patagonian steppe. Using the model, we created grass and shrub monocultures and mixtures, controlled root overlap and grass water-use efficiency (WUE) to simulate gradients of biodiversity, resource partitioning and facilitation. The presence of shrubs facilitated grass growth by increasing its WUE and in turn increased the sampling effect, whereas root overlap (resource partitioning) had, on average, no effect on sampling effect. Interestingly, resource partitioning and facilitation interacted so the effect of facilitation on sampling effect decreased as resource partitioning increased. Sampling effect was enhanced by the difference between the two functional groups in their efficiency in using resources. Morphological and physiological differences make one group outperform the other; once these differences were established further differences did not enhance the sampling effect. In addition, grass WUE and root overlap positively influence the biodiversity effect but showed no interactions. [ABSTRACT FROM AUTHOR]