Daniel S. Chapman1, Iain D. M. Gunn2, Henrietta E. K. Pringle3, Gavin M. Siriwardena3, Philip Taylor2, Stephen J. Thackeray4, Nigel J. Willby1 and Laurence Carvalho2
1Biological and Environmental Sciences, University of Stirling, Stirling, FK9 4LA, UK
2Centre for Ecology & Hydrology, Penicuik, EH26 0QB, UK
3British Trust for Ornithology, The Nunnery, Thetford, IP24 2PU, UK
4Centre for Ecology & Hydrology, Lancaster Environment Centre, Library Avenue, Lancaster, LA1 4AP, UK
Hotspots of human activity act as hubs for ecosystem disturbance and non-native species introduction, from which invading populations disperse and spread. As such, connectivity to locations used by humans may have an important influence on large-scale patterns of biological invasion. Moreover, in freshwater ecosystems, this connectivity may reflect preferential dispersal of invading species within the hydrological network. Here, we tested how well the connectivity to human activities explains invasion of freshwater ecosystems using 125 species of non-native plants, birds, crustaceans, fish and molluscs across England, UK. We first predicted spatial gradients in human recreation, fishing and water sports using machine learning, demonstrating the importance of vehicle parking, fishing and boating infrastructure for human activity. We then developed a range of connectivity indices, in which human influence percolated away from activity hotspots in all directions (spatial connectivity) or within the hydrological network (downstream, upstream and along-channel connectivity). Connectivity to human activities was positively related to invasion by all taxonomic groups. Furthermore, the human connectivity index that best explained the invasion of each group was generally consistent with its predominant human spread pathway and dispersal mode. For example, fishing and water sports both disturb ecosystems and spread aquatic non-native species and had stronger associations with invasion than general recreation or urban land cover. In addition, downstream human connectivity was most important for mainly aquatic and passively dispersed groups, such as plants, while by contrast spatial connectivity was most important for groups with overland dispersal capacity, such as birds. These findings support the hypothesis that the distributions of invasive non-native species are structured by an interaction between human activity, species dispersal and spread behaviour. By modelling human activity, network connectivity and invasion, we offer a general framework for inferring invasion processes from spatial data and improving predictions of risk that should assist in prioritizing surveillance and management for invasive non-native species.