SP6: Plant animal-interactions - pollination, parasitism, and seed dispersal

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Land-use intensification is an important driver of the loss of biodiversity locally (α-diversity) and, due to more homogenous landscapes, also on the regional level, with communities becoming more similar (decreasing β-diversity) with decreasing habitat heterogeneity among patches. Since higher α-diversity translates into higher levels of ecosystem functionality decreasing β-diversity is also expected to reduce multifunctionality over larger spatial scales. Thus, by enhancing structural complexity within forest stands on the β-level landscape-level γ-multidiversity and γ-multifunctionality should increase. Plant regeneration, an essential component of maintaining biodiversity and ecosystem functions of forests, largely depends on animal-mediated functions such as pollination and seed dispersal. Both functions are sensitive to forest management and disturbance, suggesting that more diverse animal communities increase resilience and performance of these functions.In this subproject we first aim to understand the impact of forest management (Enhancement of Structural Alpha complexity, ESC) on the diversity and composition of seed dispersers and pollinators, on their interactions with plants and higher trophic levels, and on related ecosystem functions, such as seed removal rates, pollination, and parasitism. We will test whether high heterogeneity in forest management practices, as experimentally introduced by Enhanced Structural Beta Complexity (ESBC), increases the turnover of seed-disperser and pollinator species and/or functional group (and parasitoids) and translates into complementary species interactions, increasing seed dispersal and pollination rates at the landscape scale. We expect a higher γ-diversity and, importantly, a higher γ-multifunctionality in seed dispersal and pollination in landscapes with ESBC practices, than in control districts. We will quantify the taxonomic, functional and phylogenetic diversity of invertebrate seed-dispersers and pollinators, and their parasites on all patches. Seed-removal rate will be quantified in relation to the functional diversity of the respective groups by monitoring removal of seeds with camera traps. Plant-pollinator interaction networks will be calculated based on observed plant-pollinator interactions complemented with metabarcoded pollen samples collected from the body surface of pollinators. Pollination limitation and seed set will be measured by experimental pollinator exclusion and supplementary pollination on three focal plant species. Site-specific parasitism rates will be monitored in trap-nesting bees and wasps to enable the establishment of tritrophic networks. By investigating the diversity of seed-dispersers and pollinators and two crucial functions in plant reproduction our subproject will substantially contribute to our understanding on what kind of forest management is needed to counteract ongoing species and ecosystem function losses at local and landscape scales.