Trophic interactions across tree regeneration stages

更广泛的研究背景：Janzen-Connell假说指出，物种丰富的森林生态系统中的树木多样性是由营养相互作用维持的，这些相互作用对树木的招募产生不利影响，并与同种新枝的密度呈正相关，与距母树的距离呈负相关。在这一过程中重要的相互作用是种子捕食和幼苗草食。虽然许多关于昆虫介导的营养相互作用的研究集中在单一树种上，但这最终是一个群落水平的假设。假设：在BEF-中国实验中，我们建议以昆虫为中心的观点来研究跨树木更新阶段的植物-捕食者和植物-食草动物的相互作用。我们假设(I)树木更新，(Ii)扩散前后种子捕食和苗木食草的相关功能，以及(Iii)通才和专家对这些功能的贡献将随着树木多样性的梯度而变化，(Iv)这些功能中的Janzen-Connell效应将取决于树木和昆虫种子捕食者和草食动物的群落组成。方法：我们将用观察和实验的方法量化具有不同果实特性的果树物种的更新阶段以及扩散前后种子捕食和苗木食草。在所有核心地块中，我们将借助种子诱捕器在选定树种的个体下研究预扩散的种子捕食。早熟和成熟果实的套袋将有助于识别昆虫捕食者和散布前阶段的捕食程度。将使用所选树种的种子卡在不包括脊椎动物或脊椎动物和无脊椎动物的笼子中或允许种子捕食者不受阻碍地进入笼子中，研究散布后的种子捕食行为。在所有VIP地块中，我们将评估自然招聘成功。对于选定的树种，我们也会评估因昆虫食草性和真菌感染对后代造成的叶片损害。我们还将对我们选定的树种进行发芽和苗木食草性的实验评估，方法是在无脊椎动物中添加种子和幼苗，并在家中和远方的情况下沿着树木多样性梯度进行对照。提供这些功能的昆虫制剂的鉴定将得到分子技术的支持。创新：我们将从昆虫中心论的角度研究Janzen-Connell对种子捕食以及幼苗萌发和草食的影响，这是树木繁殖过程中的关键生命阶段。通过试图确定种子捕食和草食的因素，我们将在亚热带森林生态系统中增加营养网络的决定性组成部分。总之，我们的方法将补充我们的基本知识，即物种如何在这个系统中跨营养水平相互作用，从而如何维持树木多样性。

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.