Abstract
Suboptimal environmental conditions are ubiquitous in nature and commonly drive the outcome of biological interactions in community processes. Despite the importance of biological interactions for community processes, knowledge on how species interactions are affected by a limiting resource, for example, low food availability, remains limited. Here, we tested whether variation in food supply causes nonadditive consumption patterns, using the macroinvertebrate community of intertidal sandy beaches as a model system. We quantified isotopically labeled diatom consumption by three macroinvertebrate species (Bathyporeia pilosa, Haustorius arenarius, and Scolelepis squamata) kept in mesocosms in either monoculture or a three‐species community at a range of diatom densities. Our results show that B. pilosa was the most successful competitor in terms of consumption at both high and low diatom density, while H. arenarius and especially S. squamata consumed less in a community than in their respective monocultures. Nonadditive effects on consumption in this macroinvertebrate community were present and larger than mere additive effects, and similar across diatom densities. The underlying species interactions, however, did change with diatom density. Complementarity effects related to niche‐partitioning were the main driver of the net diversity effect on consumption, with a slightly increasing contribution of selection effects related to competition with decreasing diatom density. For the first time, we showed that nonadditive effects of consumption are independent of food availability in a macroinvertebrate community. This suggests that, in communities with functionally different, and thus complementary, species, nonadditive effects can arise even when food availability is low. Hence, at a range of environmental conditions, species interactions hold important potential to alter ecosystem functioning.
Highlights
We document a strong influence of diatom density on diatom consumption by intertidal macroinvertebrate species, both for single species and in species mixtures
The nonadditive effects on consumption observed in this intertidal macroinvertebrate community were independent from diatom density and concomitant changes in macroinvertebrate species interactions
We found that B. pilosa remained the most successful species in terms of consumption, with a higher consumption than S. squamata and H. arenarius in community
Summary
To investigate the effect of diatom density on consumption by the three macroinvertebrate species both in monoculture and in community, we performed a mesocosm experiment in a fully controlled climate room in which diatom density was manipulated. Diatom consumption by the three macroinvertebrate species over the experimental period varied strongly (maximum consumption was 0.24, 0.10, and 0.14 mg diatom/mg animal for B. pilosa, H. arenarius, and S. squamata, respectively) with diatom density and differed between monocultures and communities (Figure 1). An in-d epth analysis is given by separate comparisons for each level of diatom density Both macroinvertebrate species (two-way ANOVA, df = 2, F = 14.1, p < .001) and community composition (two-way ANOVA, df = 1, F = 10.6, p < .01) had a significant effect on diatom consumption at FIGURE 1 Diatom consumption of three macroinvertebrate species (b, Bathyporeia pilosa; h, Haustorius arenarius; s, Scolelepis squamata) at three different diatom densities (percentage dilution of ad libitum diatom supply) either in monoculture (Mono) or in a three- species community (Com). For the net diversity effect, the selection effect was canceled out by a slightly higher complementarity effect at high diatom density (Figure 2)
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