DOI: 10.5061/dryad.18931zcs6
title: Invasion of freshwater ecosystems is promoted by network connectivity to hotspots of human activity

description: Aim: Hotspots of human activity are focal points for ecosystem disturbance
 and non-native introduction, from which invading populations disperse and
 spread. As such, connectivity to locations used by humans may influence
 the likelihood of invasion. Moreover, connectivity in freshwater
 ecosystems may follow the hydrological network. Here we tested whether
 multiple forms of connectivity to human recreational activities promotes
 biological invasion of freshwater ecosystems. Location: England, UK. Time
 period: 1990-2018. Major taxa studied: 126 non-native freshwater birds,
 crustaceans, fish, molluscs and plants. Methods: Machine learning was used
 to predict spatial gradients in human recreation and two high risk
 activities for invasion (fishing and water sports). Connectivity indices
 were developed for each activity, in which human influence decayed from
 activity hotspots according to Euclidean distance (spatial connectivity)
 or hydrological network distance (downstream, upstream and along-channel
 connectivity). Generalised linear mixed models identified the connectivity
 type most associated to invasive species richness of each group, while
 controlling for other anthropogenic and environmental drivers. Results:
 Connectivity to humans generally had stronger positive effects on invasion
 than all other drivers except recording effort. Recreation had stronger
 influence than urban land cover, and for most groups high risk activities
 had stronger effects than general recreation. Downstream human
 connectivity was most important for invasion by most of the groups,
 potentially reflecting predominantly hydrological dispersal. An exception
 was birds, for which spatial connectivity was most important, possibly
 because of overland dispersal capacity. Main conclusions: These findings
 support the hypothesis that freshwater invasion is partly determined by an
 interaction between human activity and species dispersal in the
 hydrological network. By comparing alternative connectivity types for
 different human activities, our approach could enable robust inference of
 specific pathways and spread mechanisms associated with particular taxa.
 This would provide evidence to support better prioritisation of
 surveillance and management for invasive non-native species.
description: Raster files showing estimated relative spatial gradients in the
 intensity of all recreation, fishing and watersports in England are
 contained within files: 
 fishing.tif recreation.tif
 watersports.tif  These gradients
 were produced by modelling destinations of visits to freshwater ecosystems
 (lakes, rivers and canals) in the Monitor of Engagement with the Natural
 Environment survey data (Natural England 2017). Visit locations within
 this dataset were modelled using machine learning to generate gradients in
 relative visit intensity. The files are in geoTIFF format 1x1 km rasters
 with OSGB 1936 British National Grid projection (EPSG:27700).
   In addition, indices of connectivity to
 these human activity gradients are contained in the other raster files.
 The file name indicates: the human activity
 (recreation, fishing, watersports) the form of
 connectivity (sp2d = spatial, down = downstream, up = upstream, along =
 along-channel) the distance decay in connectivity
 (x_km)    
 <strong>Reference</strong> Natural
 England (2017) <i>Monitor of Engagement with the Natural
 Environment: The National Survey on People and the Natural Environment.
 Technical Report to the 2009-16 surveys</i>, Natural England,
 Peterborough, UK