Clustered or scattered? The impact of habitat distribution on establishment dynamics

One of the major predictors of establishment success for an introduced species is the match between its intrinsic characteristics and the biotic and abiotic conditions of its new environment. Yet, the introduction area is likely a landscape made up of heterogenous habitats. Right after their introduction, individuals might disperse across the landscape and colonize other habitat patches. The quality of the habitat surrounding the introduction site is thus as critical to the persistence of introduced population as the quality of the introduction site itself. The spatial distribution of favorable habitats across the landscape is especially important, as it will directly determine the success of secondary colonizations. Moreover, mechanisms like Allee effects or dispersal mortality can also hamper the colonization of other habitat patches, regardless of their quality. Therefore, the interplay between these mechanisms and the spatial structure of the landscape heterogeneity might impact establishement dynamics. We investigated the impact of favorable habitat clustering on establishment in a spatially structured landscape. We first simulated introductions in one-dimensional landscapes with varying parameter values for connectivity, dispersal mortality and Allee effect. The landscapes differed by the level of clustering of favorable habitat patches (either "clumped" or "scattered"). We identified combinations of parameter values promoting invasion in either the "clumped" or the "scattered" landscapes. We then tested the results from simulations by performing experimental introductions of hymenopteran parasitoids in similar artificial landscapes, for different levels of connectivity and dispersal mortality.