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Abstract
Understanding how space affects the occurrence of native and non-native species is essential for inferring processes that shape communities. However, studies considering spatial and environmental variables for the entire community – as well as for the native and non-native assemblages in a single study – are scarce for animals. Harvestmen communities in central Europe have undergone drastic turnovers during the past decades, with several newly immigrated species, and thus provide a unique system to study such questions. We studied the wall-dwelling harvestmen communities from 52 human settlements in Luxembourg and found the assemblages to be largely dominated by non-native species (64% of specimens). Community structure was analysed using Moran's eigenvector maps as spatial variables, and landcover variables at different radii (500 m, 1000 m, 2000 m) in combination with climatic parameters as environmental variables. A surprisingly high portion of pure spatial variation (15.7% of total variance) exceeded the environmental (10.6%) and shared (4%) components of variation, but we found only minor differences between native and non-native assemblages. This could result from the ecological flexibility of both, native and non-native harvestmen that are not restricted to urban habitats but also inhabit surrounding semi-natural landscapes. Nevertheless, urban landcover variables explained more variation in the non-native community, whereas coverage of semi-natural habitats (forests, rivers) at broader radii better explained the native assemblage. This indicates that some urban characteristics apparently facilitate the establishment of non-native species. We found no evidence for competitive replacement of native by invasive species, but a community with novel combination of native and non-native species.
Highlights
Urban areas are recognized as centres of biological invasions, and there is strong empirical support for a gradient of increasing species richness and abundance of non-native species at the expense of native species towards highly urbanized areas [1,2,3,4,5]
Since our study focused on house-dwelling harvestmen, we included the coverage of Buildings in the 500 m radius as obtained from a Luxembourg-specific layer as a fine-scale parameter in addition to CORINE landcover (CLC) landcover variables
The expansive Mediterranean species Opilio canestrinii, which has probably colonized the country since the 1980s, is by far the most common species dominating communities (53.5% of all specimens) and found at 94% of all localities
Summary
Urban areas are recognized as centres of biological invasions, and there is strong empirical support for a gradient of increasing species richness and abundance of non-native species at the expense of native species towards highly urbanized areas [1,2,3,4,5]. Some analyses suggest that native communities could be primarily structured by environmental conditions, whereas non-native communities are predominantly structured by human-mediated dispersal [11,12]. In combination with dispersal limitation, anthropogenic transport may result in autogenic spatial structure of non-native communities which is referred to as spatially autocorrelated distribution [13,14]. Recently spatial structure was analysed with respect to urban communities [18,19]. Using Moran’s eigenvector maps (MEM) to estimate the spatial component, Sattler et al [20] found very little spatial variation in urban communities of individual cities of three distinct taxa (spiders, bees, birds). The authors suggested that the absence of spatial structure may be a typical feature of urban species assemblages, owing to the high degree of anthropogenic disturbance. The general value of this suggestion needs to be tested with empirical studies from additional regions and taxa
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