Network approach to metacommunities with passive dispersal mediated by ocean flows and wind fields

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According to the overarching goals of the research units our project will focus on the role of passive dispersal in the emergence of biodiversity patterns in metacommunities. Our aim is to bring together two different modelling approaches: the theory of island biogeography with the idea of connectivity graphs reflecting passive dispersal (of seeds) by ocean flows and predominant wind fields on two different spatial scales (regional: 10-100km and global: 100km-1000km). Therefore, we will combine modelling of meta food webs as networks of networks, i.e. having a food web in island (node of the network) which is linked to other islands by a connectivity graph which is entirely determined by hydrodynamic and atmospheric flows as well as movement traits like size, density and/or terminal velocity of seeds. This connectivity graph reflecting the probabilities of different seeds to reach other islands possesses a strong seasonal and annual variability due to variable weather conditions. Employing those network models of interconnected food webs, we study the interplay between movement, tolerance and interaction traits in highly dynamic environments, thereby contributing to the main objectives of the research unit (hypothesis H1). We study the impact of the variability of connectivity graphs on source-sink dynamics, colonization and rescue effects at the base of the food web and the propagation of these effects to higher trophic levels. With this investigation we will gain insights into the role of dynamic passive dispersal for the stability of meta-ecosystems (hypothesis H2) and the emergence of heterogeneous biodiversity patterns across islands. Furthermore, this network approach can be used to compare the dichotomic role of passive and active dispersal, since passive dispersal facilitates destabilization and inhomogeneous distributions of species across a meta-ecosystem due to the predominantly uni-directional dispersal, while active dispersal being mainly bi-directional leads to a homogenization and stabilization (hypothesis H3). We validate our results on the impact of passive dispersal on the regional scale with data from the colonization of an emerging island in the German Bight (from SP1) and on the global scale with abundance data of various species from 8 different archipelagos worldwide (from SP8 and SP9).