Trophic interactions across tree regeneration stages

点击翻译按钮获取中文摘要

Wider research context: The Janzen-Connell hypothesis states that tree diversity in species-rich forest ecosystems is maintained by trophic interactions that adversely affect tree recruitment and are positively related to density of conspecific recruits and negatively to distance from mother trees. Important interactions in this process are seed predation and seedling herbivory. While many studies testing the Janzen-Connell hypothesis on insect-mediated trophic interactions focused on single tree species, it is ultimately a community-level hypothesis.Hypotheses: Here we propose to study plant-predator and plant-herbivore interactions across tree regeneration stages with an entomocentric view of the Janzen-Connell hypothesis along a tree diversity gradient in the BEF-China experiment. We hypothesize that (i) tree recruitment, (ii) the associated function of pre- and post-dispersal seed predation as well as seedling herbivory and (iii) the contribution of generalists and specialists to these functions will vary along the gradient of tree diversity, (iv) Janzen-Connell effects in these functions will depend on community composition of trees and insect seed predators and herbivores.Methods: We will quantify regeneration stages as well as pre- and post-dispersal seed predation and seedling herbivory of selected fruiting tree species with differing fruit traits with observational and experimental approaches. In all core plots, we will study pre-dispersal seed predation with the help of seed traps under individuals of selected tree species. Bagging of premature and ripe fruits will help to identify insect predators and predation levels at the pre-dispersal stage. Post-dispersal seed predation will be studied using seed cards of the selected tree species in cages that exclude vertebrates or vertebrates and invertebrates or allow unhindered access of seed predators. In all VIP plots, we will assess natural recruitment success. For selected tree species, we will also assess leaf damage due to insect herbivory and fungal infection on the offspring. Germination and seedling herbivory will also experimentally be assessed for our selected tree species by adding seeds and seedlings in invertebrates exclosures and controls in home and away situations along the tree diversity gradient. Identification of insect agents delivering these functions will be supported by molecular techniques.Innovation: We will study Janzen-Connell effects for predation of seeds as well as germination of and herbivory on seedling as crucial life stages during tree reproduction with an entomocentric view. By trying to identify agents of seed predation and herbivory, we will add a decisive component of the trophic network in subtropical forest ecosystems. In concert, our approaches will complement our basic knowledge of how species interact in this system across trophic levels and thus how tree diversity is maintained.