Influence of predator defense mechanisms on predator-prey interactions in forest food-webs

• Applicant: Dr. Katja Wehner
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 419020906

Predation is an important factor that influences species interactions and may affect species distribution among forest microhabitats. The functional response of predation is shaped by multiple factors (search- and handling-time, size and body mass, population densities of predator and prey). However, many prey species have evolved defensive traits that significantly influence the predation success. Predator-prey interactions of soil arthropods in forest microhabitats are complex and difficult to monitor in nature due to the small size of the species involved and the complexity of the microhabitats. Oribatid mites are ideal models to investigate the structure and dynamics of predator-prey interactions in forest microhabitats because (a) they are extremely old and among the first animals on land, (b) they are ubiquitous on tree bark, in grassy sods, litter, dead wood, mosses and lichens and may play an important role as prey organisms in forest food webs due to their high abundances and (c) they evolved several effective predator-defense mechanisms and hence were hypothesized to somehow live in a functional “enemy-free space”. Predator-defense mechanisms in adult oribatids comprise morphological and chemical aspects. Morphological adaptations are permanent and comprise strong hardening of the cuticle, ptychoidy, and pteromorphes. Chemical defense is a dynamical mechanism based on the secretion of complex mixtures of aromatics, terpenes, hydrocarbons, alkaloids and cyanogenic compounds. The distribution of oribatid mite species with either morphological and/or chemical defense in different forest microhabitats may depend on predator abundances, predator size and body mass and predator feeding behavior. The current project aims to investigate the dynamics of predator-prey interactions in forest microhabitats by studying potential predator species and the ecological role of oribatid mites as prey and their potential microhabitat-specific functional trait composition against predation. In feeding experiments oribatid mite species found on tree bark, grass sods, litter, dead wood, mosses, and lichens will be confronted with predatory arthropods with different compositions of predatory adaptations (e.g. small/large size, biting/sucking, foraging strategies). Predators will be characterized by their body mass, size, the functional morphology of their mouthparts (feeding behavior) and oribatid mites will be characterized by their morphological defensive traits and their defensive secretions. Furthermore, chemical defense will be manipulated prior to feeding experiments, i.e. specimens will be chemically disarmed and their defense success will be compared to that of chemically defended specimens. Additionally, the degree of sclerotization of the model organism Archegozetes longisetosus will be modified by culturing specimens on wheatgrass with different amounts of the amino acid tyrosine/phenylalanine which are essentially involved in sclerotization.

• DFG Programme: Research Grants