Species interactions under global change: can ecosystem processes be maintained in species assemblages with altered species composition?

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Global changes are predicted to alter the distribution of species. This will inevitably also change the species composition of local species assemblages. However, we currently lack an understanding of the consequences of altered species compositions for the maintenance of ecological processes in local species assemblages.Many key ecological processes, e.g. predation, seed-dispersal or pollination, involve species interactions, and within a given ecological process, each species fulfills a certain functional role. Changes in the species composition in local species assemblages might disrupt interactions between species, e.g. due to local extinctions, which could ultimately lead to the loss of distinct functional roles. The magnitude of these losses, however, depends on the degree to which a local interaction network can be re-wired, that is whether the remaining and/or newly arriving species can take over the functional roles of locally extinct species.In my project I propose to investigate how changes in species composition affect the diversity of functional roles in local species assemblages, using a dataset on mutualistic plant-bird interactions from a regional seed-dispersal system. First, I will assess the functional roles of frugivorous bird species in the current local interaction networks, using a recently established method that characterizes the functional role of species via their foraging niche. I will then model the potential future distribution of all frugivorous bird species from the regional species pool and assess how this affects the species composition in the local species assemblages. I will then model potential interactions between the species in the future species assemblages based on species' foraging niches. Finally, I will investigate how the expected future changes in species compositions affect the diversity of functional roles in the local interaction networks in order to assess the degree to which the seed-dispersal mutualism is going to be affected by the expected future changes in species distributions.The modeling of species interactions and the re-wiring of interaction networks is a relatively new line of research and the methodology is still being developed. My study therefore also involves a methodological part, as I aim to refine the methodology to model individual interactions from species intrinsic properties, i.e. their functional traits. Building upon a methodological framework that I recently developed, I aim to derive a model for general relationships between the traits of interacting species groups. Once established, such a model would facilitate the modeling of interactions independent of empirical data and across spatial scales, with a wide range of potential applications, for instance, the incorporation of species interactions into models of future species distributions and the study of functional roles in ecological processes on large spatial scales.