Trophic interactions and ecological functions of ants under changing tree diversity

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Wider research context: Plant diversity relates to consumer diversity across trophic levels, but only few studies investigated in forests how producer (i.e. tree) diversity influences multitrophic interactions and ecosystem functions of arthropods. Unravelling the relationship between tree diversity and trophic interactions is crucial to understand biodiversity-ecosystem functioning relationships, which are often the outcome of interactions involving arthropods. Occurring in several trophic levels, from phytophagous to highly predacious, with most species being omnivores, ants are ideal for studying multitrophic interactions.Hypotheses: In line with preliminary results, we hypothesize that ant species diversity increases with tree diversity. Following the enemies hypothesis, we hypothesize that the degree of ant predatory life style increases with tree diversity and that functional morphospace shifts towards relatively more predacious communities. Alongside, we expect higher generality and redundancy in resource choice when tree diversity and, thus, ant diversity is high. These tree diversity-mediated changes in trophic interactions relate to realized trophic niches, with higher species-level δ15N indicating a larger share of animal-derived food objects and with broader community isotopic niche breadth indicating trophic redundancy. We hypothesise that the function ‘scavenging’ increases with tree diversity, which is mechanistically related to ant diversity and trait distribution as well as trophic positions, that are all mediated by tree diversity.Methods: In all core plots, we will quantify ant diversity and trait distribution to functionally characterise all collected species. To identify the trophic position of individual species and the entire ant community and to quantify trophic niche breadth and trophic redundancy, we will perform resource-choice experiments and measure δ15N isotope values. We will also test which traits relate to trophic niche breadth and relative trophic position. To link ant diversity and trophic interactions to an ecosystem function, we will measure ‘scavenging’ as the retrieval rate of standard carrion baits in the VIP plots.Innovation: Ants have, with the exception of our initial work, only rarely been studied in tree diversity experiments. By integrating across components of biological organization in a key arthropod taxon we will reveal how the interplay among tree diversity, ant diversity, trait distribution and trophic interactions influences forest ecosystem functionality. Our data will allow predicting if ant diversity decreases in simplified ecosystems and how ant-mediated functions depend on diversity and interactions across trophic levels.Primary researchers involved: This project will be conducted by Michael Staab (PI, Darmstadt) and Heike Feldhaar (Co-PI, Bayreuth), in collaboration with our Chinese partner Xiaojuan Liu (Beijing).