Classical models and empirical work of population spreads and range dynamics have generally assessed species spread in homogeneous landscapes. They thereby assume constant growth rates, random or constant local movement and no systematic change in abiotic conditions. Virtually all natural ecosystems, however, are characterized by a patchy distribution of resources affecting species’ growth rates, by environmental cues modulating species’ movement and dispersal decisions or by environmental gradients of various kinds. These factors are not only universal, but also especially prone to be affected by global changes. We addressed both theoretically as well as experimentally how heterogeneous distributions of environmental resources, environmental gradients and non-random movement of individuals affect invasion and spread dynamics. Specifically, we advanced the use of a protist microcosm system, using Tetrahymena pyriformis and Euglena gracilis, such that we could individually disentangle the role of these factors affecting invasion dynamics.
We find both theoretically and experimentally that increasing the resource autocorrelation lengths in experimental landscapes results in a reduction of average invasion speeds. Thereby, environmental heterogeneity intensifies the role of demographic stochasticity and the ability of species to plastically adjust their movement based on locally available information, eventually affecting landscape-level invasion and range shift dynamics. In addition, the presence of environmental gradients and the organisms’ ability to integrate information on those gradients slowed down population spread and invasion dynamics. Our results indicate that both resource autocorrelation length and the distribution of environmental resources are key modulators of a landscape’s susceptibility to biological invasions and must be considered for predicting or controlling biological invasions.