Locations of study areas.

<p>Small map: grey shading indicates the study region ‘Münsterland’ in Northwest Germany. Large map: locations of areas (squares) within the study region (Coordinate system: UTM 32N); grey shading represents larger forest areas. Base maps: map tiles by Stamen Design, under CC BY 3.0; data by OpenStreetMap, under CC BY SA.</p

Dispersal pathways deduced from statistical results for different types of plants.

<p>(A) Species confined to semi-natural grasslands and dispersed only short distances rely on multi-generational migration through Linear Landscape Elements (LLE). (B) Grassland species with mechanisms of long-distance dispersal (wind, animals) mainly disperse through the agricultural landscape matrix, while migration through LLE is less important. (C) Nitrophilous tall herbs find habitat on small fallow spots within the landscape matrix, and, thus, disperse through the matrix by stepwise migration from one fallow habitat to the next, if they lack mechanisms of long-distance dispersal.</p

Modelling results of Generalised Linear Mixed Models (GLMM) of Jaccard similarity vs. Euclidean distance and resistance distance for different phytosociological species groups and dispersal-distance classes.

<p>Modelling results of Generalised Linear Mixed Models (GLMM) of Jaccard similarity vs. Euclidean distance and resistance distance for different phytosociological species groups and dispersal-distance classes.</p

Predicted Jaccard similarities of relevés located on field margins at minimum and maximum values of Euclidean distance and resistance distance.

<p>Predicted Jaccard similarities of relevés located on field margins at minimum and maximum values of Euclidean distance and resistance distance.</p

Jaccard similarity vs. the isolation metrics Euclidean distance and resistance distance of linear landscape elements.

<p>Jaccard similarity was calculated for different species groups: (a, b) all vascular plant species, (c, d) species typical of <i>meadows and pastures</i>, (e, f) species with short-distance dispersal, and (g, h) species with medium-distance dispersal (cf. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0199980#pone.0199980.s002" target="_blank">S2 Table</a>). There were two types of LLE (field margins and ditches) and, consequently, three combinations of LLE types in the calculations of Jaccard similarity: margin compared with margin, margin compared with ditch, and ditch compared with ditch. Prediction curves are from binomial Generalised Linear Mixed Models (GLMM). Inset p-values (upper right corner) are from parametric bootstrap tests of the GLMM. Significance levels of simple regression slopes within LLE-type combinations: ns, not significant; *, p < 0.05; **, p < 0.01; ***, p < 0.001.</p

Effect of vegetation parameters on abundances of arthropods and the shading preference values of spiders in native and non-native urban woodlands.

<p>Only taxa/ecological preference values were analyzed which differed between native and non-native woodlands (Tables <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137723#pone.0137723.t003" target="_blank">3</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137723#pone.0137723.t004" target="_blank">4</a>). Differences were tested with GLMMs. Significant results at <i>p</i> < 0.05 are shown in bold.</p

Effects of a Major Tree Invader on Urban Woodland Arthropods

<div><p>Biological invasions are a major threat to biodiversity; however, the degree of impact can vary depending on the ecosystem and taxa. Here, we test whether a top invader at a global scale, the tree <i>Robinia pseudoacacia</i> (black locust or false acacia), which is known to profoundly change site conditions, significantly affects urban animal diversity. As a first multi-taxon study of this kind, we analyzed the effects of <i>Robinia</i> dominance on 18 arthropod taxa by pairwise comparisons of woodlands in Berlin, Germany, that were dominated by <i>R</i>. <i>pseudoacacia</i> or the native pioneer tree <i>Betula pendula</i>. As a negative effect, abundances of five arthropod taxa decreased (Chilopoda, Formicidae, Diptera, Heteroptera, Hymenoptera); 13 others were not affected. Woodland type affected species composition of carabids and functional groups in spiders, but surprisingly did not decrease alpha and beta diversity of carabid and spider assemblages or the number of endangered species. Tree invasion thus did not induce biotic homogenization at the habitat scale. We detected no positive effects of alien dominance. Our results illustrate that invasions by a major tree invader can induce species turnover in ground-dwelling arthropods, but do not necessarily reduce arthropod species abundances or diversity and might thus contribute to the conservation of epigeal invertebrates in urban settings. Considering the context of invasion impacts thus helps to set priorities in managing biological invasions and can illustrate the potential of novel ecosystems to maintain urban biodiversity.</p></div

Combined number of endangered carabid [51] and spider [50] species in native (<i>Betula pendula</i>) and non-native (<i>Robinia pseudoacacia</i>) woodlands.

<p>Differences were not significant (GLMM: <i>t</i> = -2.092, <i>p</i> = 0.066).</p

Variances in species composition (beta diversity) for a) carabids and b) spiders of native (<i>Betula pendula</i>) and non-native (<i>Robinia pseudoacacia</i>) woodlands.

<p>To test whether variances (multivariate dispersion) differed between the two woodland types, the distances of group members to the group centroid were subjected to ANOVA (carabids: <i>F</i> = 3.164, <i>p</i> = 0.092; spiders: <i>F</i> = 0.082, <i>p</i> = 0.779).</p

Measures of alpha diversity and ecological indicator values for shading and moisture (mean ± standard error) of carabid beetles and spiders in native (<i>Betula pendula</i>) and non-native (<i>Robinia pseudoacacia</i>) woodlands.

<p>Differences were tested with Gaussian GLMMs on log10(x+1) transformed data. Significant results at <i>p</i> < 0.05 are shown in bold.</p