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Copyright notice Chapters 2-13 have been either published, accepted for publication, or are in preparation for publication in international ecological journals. Copyright of the text and figures is with the authors. However, the publishers own the exclusive right to publish or use the material for their purposes. Reprint of any of the materials presented in this thesis requires permission of the publishers and of the author of this thesis. Introduction and overview Plant traits affecting herbivory on tree recruits in highly diverse subtropical forests published as: Schuldt A, Bruelheide H, Durka W, Eichenberg D, Fischer M, Kröber W, Härdtle W, Ma K, Michalski S, Palm WU, Schmid B, Welk E, Zhou H, Assmann T (2012) Plant traits affecting herbivory on tree recruits in highly diverse subtropical forests. Ecology Letters 15: 732-739 Functional and phylogenetic diversity of woody plants drive herbivory in a highly diverse forest published as: Schuldt A, Assmann T Bruelheide H, Durka W, Eichenberg D, Härdtle W, Kröber W, Michalski SG, Purschke O (2014) Functional and phylogenetic diversity of woody plants drive herbivory in a highly diverse forest. New Phytologist 202: 864-873 Early positive effects of herbivory in a large-scale forest biodiversity experiment submitted as: Schuldt A, Assmann T, Bruelheide H, Härdtle W, Li Y, Ma K, von Oheimb G, Zhang J: Early positive effects of herbivory in a large-scale forest biodiversity experiment Woody plant phylogenetic diversity mediates bottom-up control of arthropod biomass in species-rich forests published as: Schuldt A, Baruffol M, Bruelheide H, Chen S, Chi X, Wall M, Assmann T (2014) Woody plant phylogenetic diversity mediates bottom-up control of arthropod biomass in species-rich forests. Oecologia 176: 171-182 Predator diversity and abundance provide little support for the enemies hypothesis in forests of high tree diversity published as: Schuldt A, Both S, Bruelheide H, Härdtle W, Schmid B, Zhou H, Assmann T (2011) Predator diversity and abundance provide little support for the enemies hypothesis in forests of high tree diversity. PLoS ONE 6: e22905 Predator assemblage structure and temporal variability of species richness and abundance in forests of high tree diversity published as: Schuldt A, Bruelheide H, Härdtle W, Assmann T (2012) Predator assemblage structure and temporal variability of species richness and abundance in forests of high tree diversity. Biotropica 44: 793-800 Tree diversity promotes functional dissimilarity and maintains functional richness despite species loss in predator assemblages published as: Schuldt A, Bruelheide H, Durka W, Michalski SG, Purschke O, Assmann T (2014) Tree diversity promotes functional dissimilarity and maintains functional richness despite species loss in predator assemblages. Oecologia 174: 533-543 Tree diversity promotes predator but not omnivore ants in a subtropical Chinese forest published as: Staab M, Schuldt A, Assmann T, Klein AM (2014) Tree diversity promotes predator but not omnivore ants in a subtropical Chinese forest. Ecological Entomology, DOI: 10.1111/een.12143 Ant community structure during forest succession in a subtropical forest in South-East China submitted as: Staab M, Schuldt A, Assmann T, Bruelheide H, Klein AM (submitted) Ant community structure during forest succession in a subtropical forest in South- East China Effects of ants on the functional composition of spider assemblages increase with tree species richness in a highly diverse forest submitted as: Schuldt A, Staab M (submitted) Effects of ants on the functional composition of spider assemblages increase with tree species richness in a highly diverse forest Scale-dependent diversity patterns affect spider assemblages of two contrasting forest ecosystems published as: Schuldt A, Assmann T, Schaefer M (2013) Scale-dependent diversity patterns affect spider assemblages of two contrasting forest ecosystems. Acta Oecologica 49: 17-22 Non-native tree species (Pseudotsuga menziesii) strongly decreases predator biomass and abundance in mixed-species plantations of a tree diversity experiment published as: Schuldt A, Scherer-Lorenzen M (2014) Non-native tree species (Pseudotsuga menziesii) strongly decreases predator biomass and abundance in mixed-species plantations of a tree diversity experiment. Forest Ecology and Management 327: 10-17 General discussion and conclusions Biodiversity loss is one of the major results. The analyses in this thesis go beyond components of global change, affecting and the effects of mere species richness and, threatening the functioning and service where possible, incorporate functional and provisioning of ecosystems worldwide. phylogenetic data of the producer or Although much progress has been made over consumer assemblages to help unveil the the last decades in understanding the potential mechanisms and evolutionary relationships between biodiversity and dependencies underlying biodiversity effects. ecosystem functioning (BEF), much of our The studies presented in this thesis knowledge stems from simplified or relatively identify key plant functional traits and low-diverse agricultural and grassland systems. multivariate trait complexes that determine More complex systems such as forests, which herbivory levels within and among woody play a crucial role in regulating global plant species, and they show that the biogeochemical cycles and mitigating climate functional and phylogenetic diversity of change effects, have received less attention in woody plant communities strongly promotes the context of BEF research until recently. herbivore damage—indicating a strong impact This applies particularly to subtropical and of generalist herbivores that benefit from tropical forests, which contribute substantially dietary mixing of different plant species. The to primary production, carbon sequestration extent to which the distribution and diversity and climate regulation, and which harbor a of key palatability and defense traits in plant large part of terrestrial biodiversity. communities are affected by changes in plant Importantly, the functioning and biodiversity diversity thus strongly determine the strength maintenance of these forests are often of plant diversity effects on herbivory. considered to be strongly affected by trophic Likewise, a strong impact of plant interactions. Trophic complexity is phylogenetic diversity and, at the same time, a increasingly being recognized as a key lack of effect of plant species richness on determinant of biodiversity-ecosystem herbivore biomass and abundance in the functioning relationships in many ecosystems. studied forests indicate that the diversity- And yet, it is poorly explored how higher dependence of herbivore-mediated ecosystem trophic levels and their interaction effects on processes may fundamentally depend on the structure and functioning of ecosystems nonrandom associations among plant and are altered by biodiversity loss in species-rich herbivore species. Scenarios of random systems such as (sub)tropical forest, where species loss may thus underestimate the these interaction effects may be particularly consequences for ecosystem functions if these relevant. scenarios do not reflect the driving forces of The studies united in this thesis community assembly. In contrast to address major aspects of these shortcomings herbivores, overall patterns in predator and analyze the impacts of plant diversity and abundance and diversity appear to be little its loss on the diversity and functional impact affected by plant diversity in the studied forest of, and the potential interactions among, key systems. The results suggest that predator top- functional groups of primary (herbivores) and down control is not necessarily promoted by secondary consumers (predators) in forests— higher plant diversity, neither in species-rich with a primary focus on highly diverse subtropical forests nor in less diverse subtropical forests. Particular attention is temperate forests. However, differential given to (near)natural forests, as they have the responses of predator functional diversity and advantage of providing insight into ecosystem species richness to changes in plant diversity functioning based on established communities highlight the complexity of diversity patterns of plants and animals under natural even within individual trophic levels. The conditions. Experimental studies in tree results of this thesis indicate that this diversity experiments are used to back up and complexity could lead, via intraguild verify the causality of important observational interactions among predators, to plant diversity-mediated shifts in the functional herbivore damage observed in the studied structure of important predatory guilds. These forests can be expected to cause direct shifts, in turn, could potentially influence the feedbacks on the producer level. Higher overall strength of predator top-down effects. damage on more common than rare plant Altogether the results of this thesis species might lead to a positive feedback loop point to an important role of plant diversity in of bottom–up controlled herbivores on plant regulating particularly herbivore assemblage diversity maintenance, and increasing damage patterns and in mediating plant-herbivore levels with increasing plant diversity at the interactions at the levels of both individual community-level are likely to affect the way plant species and entire plant communities in plant diversity impacts on processes such as species-rich subtropical forests. Herbivores