Abstract
Central in this project is the notion that when studying the effects of habitat fragmentation and isolation on biodiversity, it is pivotal to investigate the relevant multitrophic interactions of the species of interest, how habitat changes effect these interactions and the functioning of the multitrophic system as a whole. We want to test the general hypotheses that as a result of habitat fragmentation and isolation the stability of multitrophic systems decreases because i) within multitrophic systems there are differences in dispersal ability of the participants ii) these differences can lead to local absence of the participants with the lowest dispersal capacity iii) in turn this may lead to overexploitation by species at a lower trophic level iv) these processes are enforced by habitat fragmentation and isolation. More specifically we assume that especially parasitoids or predators are susceptible to habitat fragmentation compared to their hosts leading to the absence of parasitoids in fragmented populations and a greater extinction risk of the system as a whole. Therefore, in this project we will concentrate on the sensitivity of the hervbivore to fragmentation. As a model system we will use Senecio jacobaea, its specialized herbivore Tyria jacobaeae and the specialized parasitoid Cotesia popularis. For this tritrophic system, the dispersal abilities of the component species and the effects of habitat fragmentation and isolation on the dynamics of the system will be studied both on a local and regional scale. In joint effort with projects 3 and 5 a broad scale inventory for a large number of species will be made. For the selected species the (changing) distribution of the participants of the multitrophic system will be related to habitat fragmentation, in order to study the sensitivity of the systems to fragmentation in relation to dispersal rates and other life history traits. With respect to conservation purposes this project and projects 3 and 5 in combination with the results from the theoretical study (project 1 ), should lead to an operational system to derive thresholds for spatial and temporal standards for different landscape types to be developed in project 2.
Netherlands