MultiTroph SP4

MultiTroph Cavity-nesting Hymenoptera and multi-trophic interactions

Subproject 4 aims to distinguish tree diversity driven bottom up functions, acting on quantitative interaction networks of cavity-nesting Hymenoptera across trophic levels, including their food resources and natural enemies and tests drivers of cavity-nesting community establishment under natural conditions in dead wood as alternative nests. We will focus on separated overarching objectives in three work packages (WP): Forest succession and the effects of tree diversity in multi-trophic interactions WP1 will address how tree diversity alters multi-trophic cavity-nesting Hymenoptera communities and their interactions with parasitoids. This first WP will study, for the first time, the influences of tree diversity along temporal changes of forest succession over a period of 10 years (2013-2024) at the 64 VIP plots. We will additionally analyse the relative importance of the different tree diversity components (taxonomic, functional and phylogenetic tree diversity) on cavity-nesting bees, wasps and their natural enemies in a controlled diversity gradient, installing, for the first time, reed nests at all 300 core plots. WP1 will test two hypotheses: (1) Tree diversity changes cavity-nesting communities, but only starting at the point after canopy closure with forest succession. This assumption is based on our comparison of cavity-nesting communities at the experimental sites during the first years of plot establishment with established old-growth forest plots. (2) Tree functional diversity explains higher complementarity of resources than taxonomic and phylogenetic tree diversity and should therefore be a strong predictor of the diversity of bee/wasp-parasitoid interactions. Traits affecting functions are not only related to bee and wasp feeding but also to nesting such as tree resin, which is beneficial for bee health. Multi-trophic network extension facilitated by DNA barcoding to link wasps to their herbivorous food prey WP2 will extend the parasitoid-host interactions so far studied with reed nests to prey and food resources of hosts. This provides the unique opportunity to establish a mechanistic interaction link to the experimentally controlled trophic level of forest trees. Observed multi-trophic interactions of more than two trophic levels involving primary producers are lacking across forest BEF-studies worldwide (except for investigations on trophobiotic tree-ant-Hemiptera interactions at the BEF-China sites when trees were small and leaves accessible). With the identification of herbivorous prey, we aim to establish the feeding links between herbivore-hunting wasps with trees (together with SP3). Additionally, bee pollen will be directly attributed to flowering trees. We will establish the methodology of continuous prey identifications using barcoding and ultimately metabarcoding. As this is methodologically challenging, we will establish a DNA barcoding approach optimized for high-throughput sequencing (e.g. MinION and Illumina novaseq) to study samples taken only at the subset of VIP-plots. Given the challenging data analyses of Next Generation Sequencing (NGS) data, we will rely and refine already approved data analysis pipelines and develop a reference database comprising newly generated DNA libraries and barcodes as basis for the parallel establishment of the metabarcoding approach. WP2 will test two hypotheses: (1) High-throughput barcode analysis leads to high taxonomic resolution and is needed to establish a reliable metabarcoding approach for animal and plant tissue that leads to identifications at family, genus and species levels. (2) Tree diversity explains the degree of specialisation of bees and wasps but this pattern dampens with trophic-distance to the tree food resources. Linking cavity-nesting bees, wasps and parasitoids to dead wood WP3 will use a new cavity-nesting model (already tested in urban gardens in Germany) to link the trophic interactions of Hymenoptera to dead wood (coarse woody debris) and therefore to decomposers and ants. At each VIP plot of both study sites, we will install dead wood with cavities to simulate natural conditions for cavity-nesting Hymenoptera and dead wood decomposers. By comparing exclusion of ants to ant accessing dead wood, and comparing dead wood with drilled cavities to non-prepared dead wood (SP1), we study the competition and synergies between bees, wasps, ants (SP6) and decomposers across the tree diversity gradient (SP1). WP3 tests the hypothesis that nests closer to the ground and nests allowing access for ants have low bee and wasp occupancy with little parasitism rates. This is because bee nests at suboptimal nesting conditions are described to be enemy-released. How the presence of decomposers influence the presence of bees, wasps and their parasitoids (e.g. through ecological engineering of wood-boring beetles), with and without ants, along the tree diversity gradient will be part of SP1.

2024-02-29

2024-02-29