Is there an urban effect in alien plant invasions?

Cities are known to be extraordinarily rich in alien plant species compared to rural environments. This is related to specific attributes of urban areas including the availability of natural resources and habitats (namely geological substrates and land cover), the dispersal pathways and associated propagule pressure due to trade and traffic, and the proximity many urban hubs have to rivers. Here we explored how richness and proportions of alien species introduced after the discovery of the Americas (so-called neophytes), can be explained by environmental covariates along the urbanization gradient from very rural to very urbanized grid cells. We tested whether there is a specific urban effect, either as an interaction effect of urbanized areas that changes these general relationships, or if there is an effect due to specific urban conditions. We found that the environmental covariates explaining richness as well as proportions of neophytes remain largely the same across the rural–urban gradient. There is, however, an effect of urbanized area on neophyte species richness and proportions, which also incorporates strictly urban conditions. Rivers, roads and railroads contribute disproportionately less to the increase of neophyte species diversity in more urbanized areas, which might be due to the already higher number of neophytes in cities. We argue that the conditions determining neophyte richness in cities are not fundamentally different from those in rural environments, but extend on the same environmental axis, i.e. having different positions along the gradient towards the upper end.     

Does plant phylogenetic diversity increase invertebrate herbivory in managed grasslands?

Plant diversity and land-use intensity have been shown to affect invertebrate herbivory. Several hypotheses predict positive (e.g. associational susceptibility) or negative (e.g. associational resistance) relationships of herbivory with plant species richness. Also, the strength and direction of reported relationships vary greatly between studies leading to the conclusion that relationships either depend on the specific system studied or that other unconsidered factors are more important. Here, we hypothesized that plant phylogenetic diversity is a stronger predictor of invertebrate herbivory than plant species richness because it integrates additional information about the phenotypical and functional composition of communities. We assessed the community-wide invertebrate herbivory, plant species richness and phylogenetic diversity across a range of land-use intensities including a total of 145 managed grasslands in three regions in Germany. Increasing land-use intensity decreased plant species richness and phylogenetic diversity. Plant species richness did not predict invertebrate herbivory. By contrast herbivory moderately increased with increasing plant phylogenetic diversity even after accounting for the effects of region and land use. The strength of direct effects of land-use intensity and indirect effects via altered phylogenetic diversity on herbivory, however, varied among regions. Our results suggest that increasing phylogenetic diversity of plant communities increases invertebrate herbivory probably by providing higher resource diversity. Differences between regions underline the need to account for regional peculiarities when attempting to generalize land-use effects on invertebrate herbivory.     

Do protected areas in urban and rural landscapes differ in species diversity?

Previous studies from Central Europe and North America showed that species richness is higher in urban than in rural landscapes. Do protected areas, which can be found in both city and countryside, reflect this species richness pattern? The impact of urban land-use might reduce conservation success and necessitate special management strategies. We compared species richness and species spatial turnover of selected animal and plant taxa (carabids, butterflies, snails, birds, lichens, mosses, vascular plants) in 30 protected areas in the city of Halle and 56 protected areas in the adjacent rural district of Saalkreis (Central Germany). Species were mapped by experienced biologists within a systematic species inventory. We corrected species numbers for the effects of landscape structure (e.g. size, shape and distance of habitats) which might influence species diversity beyond urbanisation effects. Butterflies, birds and lichens had significantly higher species numbers in the rural protected areas. Species spatial turnover was higher among urban areas than among rural areas or pairs of urban and rural areas for most taxa. Diversity in all taxa depended on the size of a protected area. We discussed these patterns in the context of the general urban-rural species diversity patterns. Our results indicate an increasing isolation of species assemblages with urbanisation and highlight that space for protected areas is even more limited in urban than rural areas. An effective conservation of urban species diversity should include both typical urban and semi-natural habitats to cover the full range of species living in cities.     

Where is the UK's pollinator biodiversity? The importance of urban areas for flower-visiting insects

Insect pollinators provide a crucial ecosystem service, but are under threat. Urban areas could be important for pollinators, though their value relative to other habitats is poorly known. We compared pollinator communities using quantified flower-visitation networks in 36 sites (each 1 km²) in three landscapes: urban, farmland and nature reserves. Overall, flower-visitor abundance and species richness did not differ significantly between the three landscape types. Bee abundance did not differ between landscapes, but bee species richness was higher in urban areas than farmland. Hoverfly abundance was higher in farmland and nature reserves than urban sites, but species richness did not differ significantly. While urban pollinator assemblages were more homogeneous across space than those in farmland or nature reserves, there was no significant difference in the numbers of rarer species between the three landscapes. Network-level specialization was higher in farmland than urban sites. Relative to other habitats, urban visitors foraged from a greater number of plant species (higher generality) but also visited a lower proportion of available plant species (higher specialization), both possibly driven by higher urban plant richness. Urban areas are growing, and improving their value for pollinators should be part of any national strategy to conserve and restore pollinators.     

Comparing galling insect richness among Neotropical savannas: effects of plant richness, vegetation structure and super-host presence

Plant species diversity maintains the stability of ecosystems and the diversity of consumer species such as insect herbivores. Considering that gall-inducing insects are highly specialized on their host plants and dependent on the occurrence, abundance and distribution of plants, we evaluated the diversity patterns of gall-inducing insect along Brazilian Neotropical savannas and the potential role of plant species richness, vegetation structure and super-host presence on determining these patterns. We found 1,882 individual plants that belonged to 64 different host plant species grouped in 31 families, associated to 112 galling insect species. The galling richness was positively influenced by plant species richness and the presence of the super-host genus Qualea (Vochysiaceae). Plant species richness explained 48 % of the galling richness and areas with presence of super-hosts had more than twice of galling species than areas where they were absent. On the other hand, we found no evidence that larger plants hosted more species of galling insects. We observed that for the diversity of galling insects in the Brazilian Cerrado, vegetation structure explained almost the same portion as plant richness, because structural variables did not have an effect on residuals of galling richness and plant richness regression. Our findings suggests that plant richness has a more important role on the mitigation of natural enemies and adaptive radiation of galling species, while structural aspects of the vegetation does not seem to have that effect. Furthermore, we show that the super-host taxa provide an increment in local galling richness because they present a great diversity of local number of gall morphospecies (i.e. alpha diversity) and the high turnover of morphospecies among different localities (i.e. beta diversity). Therefore we argue that the quality of resources (richness and super host presence) appears to be a most important factor for the diversity of galling insects in Neotropical systems, than the amount of resources.     

Amphibian Species Contribute Similarly to Taxonomic,but not Functional and Phylogenetic Diversity: Inferences from Amphibian Biodiversity on Emei Mountain

Understanding the relationships between species,communities,and biodiversity are important challenges in conservation ecology.Current biodiversity conservation activities usually focus on species that are rare,endemic,distinctive,or at risk of extinction.However,empirical studies of whether such species contribute more to aspects of biodiversity than common species are still relatively rare.The aim of the present study was to assess the contribution of individual amphibian species to different facets of biodiversity,and to test whether species of conservation interest contribute more to taxonomic,functional,and phylogenetic diversity than do species without special conservation status.To answer these questions,19 000 simulated random communities with a gradient of species richness were created by shuffling the regional pool of species inhabiting Emei Mountain.Differences of diversity values were then computed before and after removing individual species in these random communities.Our results indicated that although individual species contributed similarly to taxonomic diversity,their contribution to functional and phylogenetic diversity was more idiosyncratic.This was primarily driven by the diverse functional attributes of species and the differences in phylogenetic relationships among species.Additionally,species of conservation interest did not show a significantly higher contribution to any facet of biodiversity.Our results support the claims that the usefulness of metrics based only on species richness is limited.Instead,assemblages that include species with functional and phylogenetic diversity should be protected to maintain biodiversity.     

Common species have lower taxonomic diversity Evidence from the urban floras of Brussels and Rome

The species pool hypothesis claims that the large‐scale regional species pool is the chief parameter in determining small‐scale species richness through filtering of species that can persist within a community on the basis of their tolerance of the abiotic environment. Accordingly, different environmental conditions give rise to different species assemblages. From a taxonomic perspective, under the assumption of trait conservatism, co‐occurring species that experience similar environmental conditions are likely to be more taxonomically similar than ecologically distant species. The next step consists in understanding how commonness and rarity of individual species produce the observed taxonomic diversity. In this paper, the importance of environmental filtering in regulating the taxonomic structure of rare and common plant species in the urban floras of Brussels (Belgium) and Rome (Italy) is tested. First, we computed the taxonomic diversity of the rare and common species of Brussels and Rome based on the branching topology of the Linnaean taxonomic trees. Next, using a randomization procedure, we determined whether the taxonomic diversity of the rare species was significantly higher than the diversity of the common species. Results show that, for both urban floras, common species that shape the community matrix and experience similar environmental conditions have a taxonomic diversity that is significantly lower than that of the rare species that represent a relatively incidental set of species of more ‘disperse’ origin. Finally, from a conservation/management perspective our results imply that, given their high taxonomic heterogeneity, the protection of rare species is a central issue for preserving high levels of diversity in urban areas.     

云南被子植物蔷薇分支的进化历史研究

本文以云南被子植物蔷薇分支为研究对象,基于物种间的演化关系,结合其地理分布,从进化历史的角度探讨了物种、特有种、受威胁物种的种类组成及系统发育组成的分布格局,并整合自然保护地的空间分布,对生物多样性的重点保护区域进行识别。结果显示：云南被子植物蔷薇分支的物种密度与系统发育多样性、特有种密度、受威胁物种密度均呈显著正相关,云南南部和西北部是物种丰富度与系统发育多样性最为丰富的区域;就云南整体而言,蔷薇分支的标准化系统发育多样性较低;云南南部、东南部、西北部是蔷薇分支的重点保护区域。     

Avian diversity and function across the world's most populous cities

Understanding the composition of urban wildlife communities is crucial to promote biodiversity, ecosystem function and links between nature and people. Using crowdsourced data from over five million eBird checklists, we examined the influence of urban characteristics on avian richness and function at 8443 sites within and across 137 global cities. Under half of the species from regional pools were recorded in cities, and we found a significant phylogenetic signal for urban tolerance. Site-level avian richness was positively influenced by the extent of open forest, cultivation and wetlands and avian functional diversity by wetlands. Functional diversity co-declined with richness, but groups including granivores and aquatic birds occurred even at species-poor sites. Cities in arid areas held a higher percentage of regional species richness. Our results indicate commonalities in the influence of habitat on richness and function, as well as lower niche availability, and phylogenetic diversity across the world's cities.     

Invasive species removal increases species and phylogenetic diversity of wetland plant communities

Plant invasions result in biodiversity losses and altered ecological functions, though quantifying loss of multiple ecosystem functions presents a research challenge. Plant phylogenetic diversity correlates with a range of ecosystem functions and can be used as a proxy for ecosystem multifunctionality. Laurentian Great Lakes coastal wetlands are ideal systems for testing invasive species management effects because they support diverse biological communities, provide numerous ecosystem services, and are increasingly dominated by invasive macrophytes. Invasive cattails are among the most widespread and abundant of these taxa. We conducted a three‐year study in two Great Lakes wetlands, testing the effects of a gradient of cattail removal intensities (mowing, harvest, complete biomass removal) within two vegetation zones (emergent marsh and wet meadow) on plant taxonomic and phylogenetic diversity. To evaluate native plant recovery potential, we paired this with a seed bank emergence study that quantified diversity metrics in each zone under experimentally manipulated hydroperiods. Pretreatment, we found that wetland zones had distinct plant community composition. Wet meadow seed banks had greater taxonomic and phylogenetic diversity than emergent marsh seed banks, and high‐water treatments tended to inhibit diversity by reducing germination. Aboveground harvesting of cattails and their litter increased phylogenetic diversity and species richness in both zones, more than doubling richness compared to unmanipulated controls. In the wet meadow, harvesting shifted the community toward an early successional state, favoring seed bank germination from early seral species, whereas emergent marsh complete removal treatments shifted the community toward an aquatic condition, favoring floating‐leaved plants. Removing cattails and their litter increased taxonomic and phylogenetic diversity across water levels, a key environmental gradient, thereby potentially increasing the multifunctionality of these ecosystems. Killing invasive wetland macrophytes but leaving their biomass in situ does not address their underlying mechanism of dominance and is less effective than more intensive treatments that also remove their litter.     

Proportion of exotics and relatedness of host species mediate the positive effect of plant richness on the species richness of fruit flies

1. All else being equal, the greater the local species richness of plants, the greater the number of associated herbivore species. Because most herbivore insects feed on a subset of closely related plant species, plant phylogenetic diversity is expected to play a key role in determining the number of herbivore species. What is not well known, however, is how an increase in the species richness of exotic plants affects the species richness of herbivores. 2. In this study, we used plant–fruit fly interactions to investigate the influence of the proportion and species richness of exotic host plants on the species richness of herbivorous insects. We also tested whether the phylogenetic diversity of host plants increases when the number of exotic plant species increases. 3. We found that the species richness of fruit flies is more accurately predicted by the richness of native host plants than by total plant species richness (including both native and exotic species). The proportion of exotic host species and the phylogenetic diversity of host plants had negative and positive effects, respectively, on the species richness of fruit flies. 4. Our findings suggest that a positive effect of plant richness on herbivore richness occurs only when an increase in plant diversity involves plant species with which native herbivores share some evolutionary history.     

Global loss of avian evolutionary uniqueness in urban areas

Urbanization, one of the most important anthropogenic impacts on Earth, is rapidly expanding worldwide. This expansion of urban land‐covered areas is known to significantly reduce different components of biodiversity. However, the global evidence for this effect is mainly focused on a single diversity measure (species richness) with a few local or regional studies also supporting reductions in functional diversity. We have used birds, an important ecological group that has been used as surrogate for other animals, to investigate the hypothesis that urbanization reduces the global taxonomical and/or evolutionary diversity. We have also explored whether there is evidence supporting that urban bird communities are evolutionarily homogenized worldwide in comparison with nonurban ones by means of using evolutionary distinctiveness (how unique are the species) of bird communities. To our knowledge, this is the first attempt to quantify the effect of urbanization in more than one single diversity measure as well as the first time to look for associations between urbanization and phylogenetic diversity at a large spatial scale. Our findings show a strong and globally consistent reduction in taxonomic diversity in urban areas, which is also synchronized with the evolutionary homogenization of urban bird communities. Despite our general patterns, we found some regional differences in the intensity of the effect of cities on bird species richness or evolutionary distinctiveness, suggesting that conservation efforts should be adapted locally. Our findings might be useful for conservationists and policymakers to minimize the impact of urban development on Earth's biodiversity and help design more realistic conservation strategies.     

上海居住区植物多样性的均质化

居住区植被是我国城市植被的重要组成体,其多样性的分布格局将影响城市植被的多样性.通过对上海市中心、市郊和郊县居住区的植被调查,比较了城乡梯度上居住区绿化观赏植物、杂草和自生逃逸植物的多样性和物种组成.结果表明：城乡梯度上,绿化观赏植物和杂草的丰富度不存在显著差异,而市郊自生逃逸植物的丰富度最高;不同城乡梯度居住区中,绿化观赏植物、杂草和自生逃逸植物的物种组成相似,其中40％～50％的物种为共有种.上海城镇居住区植物均质化的主要原因是几近雷同的居住区建造风格和绿化形式,制约了绿化植物的使用和异质生境的营造.     

Mapping Biodiversity and Setting Conservation Priorities for SE Queensland’s Rainforests Using DNA Barcoding

Australian rainforests have been fragmented due to past climatic changes and more recently landscape change as a result of clearing for agriculture and urban spread. The subtropical rainforests of South Eastern Queensland are significantly more fragmented than the tropical World Heritage listed northern rainforests and are subject to much greater human population pressures. The Australian rainforest flora is relatively taxonomically rich at the family level, but less so at the species level. Current methods to assess biodiversity based on species numbers fail to adequately capture this richness at higher taxonomic levels. We developed a DNA barcode library for the SE Queensland rainforest flora to support a methodology for biodiversity assessment that incorporates both taxonomic diversity and phylogenetic relationships. We placed our SE Queensland phylogeny based on a three marker DNA barcode within a larger international rainforest barcode library and used this to calculate phylogenetic diversity (PD). We compared phylo- diversity measures, species composition and richness and ecosystem diversity of the SE Queensland rainforest estate to identify which bio subregions contain the greatest rainforest biodiversity, subregion relationships and their level of protection. We identified areas of highest conservation priority. Diversity was not correlated with rainforest area in SE Queensland subregions but PD was correlated with both the percent of the subregion occupied by rainforest and the diversity of regional ecosystems (RE) present. The patterns of species diversity and phylogenetic diversity suggest a strong influence of historical biogeography. Some subregions contain significantly more PD than expected by chance, consistent with the concept of refugia, while others were significantly phylogenetically clustered, consistent with recent range expansions.     

Ecosystem Functions across Trophic Levels Are Linked to Functional and Phylogenetic Diversity

In experimental systems, it has been shown that biodiversity indices based on traits or phylogeny can outperform species richness as predictors of plant ecosystem function. However, it is unclear whether this pattern extends to the function of food webs in natural ecosystems. Here we tested whether zooplankton functional and phylogenetic diversity explains the functioning of 23 natural pond communities. We used two measures of ecosystem function: (1) zooplankton community biomass and (2) phytoplankton abundance (Chl a). We tested for diversity-ecosystem function relationships within and across trophic levels. We found a strong correlation between zooplankton diversity and ecosystem function, whereas local environmental conditions were less important. Further, the positive diversity-ecosystem function relationships were more pronounced for measures of functional and phylogenetic diversity than for species richness. Zooplankton and phytoplankton biomass were best predicted by different indices, suggesting that the two functions are dependent upon different aspects of diversity. Zooplankton community biomass was best predicted by zooplankton trait-based functional richness, while phytoplankton abundance was best predicted by zooplankton phylogenetic diversity. Our results suggest that the positive relationship between diversity and ecosystem function can extend across trophic levels in natural environments, and that greater insight into variation in ecosystem function can be gained by combining functional and phylogenetic diversity measures.     

Species richness and evenness respond in a different manner to propagule density in developing prairie microcosm communities

Diversity has two basic components: richness, or number of species in a given area, and evenness, or how relative abundance or biomass is distributed among species. Previously, we found that richness and evenness can be negatively related across plant communities and that evenness can account for more variation in Shannon’s diversity index (H′) than richness, which suggests that relationships among diversity components can be complex. Non-positive relationships between evenness and richness could arise due to the effects of migration rate or local species interactions, and relationships could vary depending on how these two processes structure local communities. Here we test whether diversity components are equally or differentially affected over time by changes in seed density (and associated effects on established plant density and competition) in greenhouse communities during the very early stages of community establishment. In our greenhouse experiment, we seeded prairie microcosms filled with bare field soil at three densities with draws from a mix of 22 grass and forb species to test if increased competition intensity or seedling density would affect the relationships among diversity components during early community establishment. Increased seed density treatments caused diversity components to respond in a different manner and to have different relationships with time. Richness increased linearly with seed density early in the experiment when seedling emergence was high, but was unrelated to density later in the experiment. Evenness decreased log-linearly with seed densities on all sampling dates due to a greater dominance by Rudbeckia hirta with higher densities. Early in the experiment, diversity indices weakly reflected differences in richness, but later, after the competitive effects of Rudbeckia hirta became more intense, diversity indices more strongly reflected differences in evenness. This suggests that species evenness and diversity indices do not always positively covary with richness. Based on these results, we suggest that evenness and richness can be influenced by different processes, with richness being more influenced by the number of emerging seedlings and evenness more by species interactions like competition. These results suggest that both diversity components should be measured in plant diversity studies whenever it is possible.     

欧亚大陆东部毛茛科植物多样性格局及主导因子

毛茛科是真双子叶植物的基部类群之一, 包含多种药用植物, 具有较高的保护价值, 但关于毛茛科物种多样性和谱系多样性大尺度格局及其影响因子的研究还比较匮乏, 特别是以较高分辨率分布数据为基础的物种多样性格局研究尚未见报道。本文旨在: (1)建立欧亚大陆东部毛茛科植物分布数据库, 估算不同生活型物种多样性和谱系多样性格局, 并探究格局的形成机制。(2)分析毛茛科物种多样性和谱系多样性的相关关系, 确定多样性热点地区, 为毛茛科保护规划提供依据。根据中国、哈萨克斯坦、吉尔吉斯斯坦、塔吉克斯坦、土库曼斯坦、乌兹别克斯坦、蒙古和俄罗斯等国家的区域和地方植物志, 建立了“欧亚大陆东部地区毛茛科物种分布数据库”。该数据库包含了欧亚大陆东部地区1,688种毛茛科物种的分布数据, 空间分辨率为100 km × 100 km。在此基础上, 估算了毛茛科全部及不同生活型的物种多样性和谱系多样性格局, 并利用广义线性模型和等级方差分离方法分析了毛茛科物种和谱系多样性格局与环境因子的关系。最后比较了物种多样性和谱系多样性的相关关系, 确定了毛茛科的古热点地区。结果显示: (1)欧亚大陆东部毛茛科植物物种和谱系多样性均呈明显的纬度格局, 且在山区具有较高的多样性。(2)毛茛科植物物种和谱系多样性受现代气候、地形异质性和末次冰期以来的气候变化的共同影响, 但不同影响因子的相对贡献率在物种和谱系多样性及不同生活型之间差异显著。(3)中高纬度地区的谱系多样性高于给定物种数的预期, 是毛茛科的古热点地区, 在毛茛科保护规划中应受到重视。     

Does herbivore diversity depend on plant diversity? The case of California butterflies

It is widely believed that the diversity of plants influences the diversity of animals, and this should be particularly true of herbivores. We examine this supposition at a moderate spatial extent by comparing the richness patterns of the 217 butterfly species resident in California to those of plants, including all 5,902 vascular plant species and the 552 species known to be fed on by caterpillars. We also examine the relationships between plant/butterfly richness and 20 environmental variables. We found that although plant and butterfly diversities are positively correlated, multiple regression, path models, and spatial analysis indicate that once primary productivity (estimated by a water-energy variable, actual evapotranspiration) and topographical variability are incorporated into models, neither measure of plant richness has any relationship with butterfly richness. To examine whether butterflies with the most specialized diets follow the pattern found across all butterflies, we repeated the analyses for 37 species of strict monophages and their food plants and found that plant and butterfly richness were similarly weakly associated after incorporating the environmental variables. We condude that plant diversity does not directly influence butterfly diversity but that both are probably responding to similar environmental factors.     

北京城市生态系统植物种类构成及其分布特征

为了认识北京城市生态系统植物的构成特点、变化趋势及保护城市植物多样性 ,进而为北京城市绿化提供科学基础 ,对北京城区五环内各功能类型的植物进行了抽样调查、标本采集、鉴定和研究。结果表明 :(1)北京城区五环内共有维管束植物 99科30 7属 5 36种 ,其中北京本地种 2 79种 ,占总种数的 5 2 .0 5 % ,国内引进种 15 0种 ,占总种数的 2 7.99% ,国外引进种 10 7种 ,占总种数的 19.96 %。 (2 )北京城区植物属的区系地理成分以北温带成分为主 ,占城区总属数的 2 1.0 5 % ,远低于全北京植物北温带成分占 30 .30 %的比例 ;温带亚洲物种、旧世界温带物种、世界分布物种的比例都呈减少趋势 ;除旧世界热带物种成分外 ,其它热带物种成分的比例都有所增加。(3)城区各功能区物种丰富度从大到小的顺序为公园、学校校园、居民小区、道路、体育中心及单位场院、广场及公共建筑。公园、学校校园植物的总种数都占城区五环内植物总种数的 5 0 %以上 ,是城区植物的物种库。但本地植物物种比例在所有的功能区中均较低 ,甚至在公园与学校校园 ,本地物种的比例也分别只有 5 3.86 %与 5 2 .5 2 % ,居民小区和广场及公共建筑的北京本地种比例分别只有 4 1.39%和 4 0 .2 3%。 (4 )公园的乔、灌木植物多样性最高 ,荒地的草本植物     

Alien species richness is currently unbounded in all but the most urbanized bird communities

Urban areas suffer high pressure of introductions of alien species compared to other habitats due to intensive human activities. As trading globally continues to rise, more species will likely be introduced into urban areas. To determine whether this increase in introduction pressure will lead to increased alien species richness in urban areas, or whether other processes would act to impose an upper limit on species richness, we examined how the shape of the relationship between alien species richness and the number of introduced species over time (i.e. introduction pressure) varies along gradients of urbanization. We collected species composition data from urban bird surveys worldwide and used a global database of alien bird introductions to quantify how many species have been introduced over time at different sites. We found that urbanization gradually modified the shape of the studied relationship from linear to asymptotic. Only communities in extremely urbanized environments were associated with an asymptotic relationship, suggesting that alien bird richness has likely not reached its ecological limit in most urban areas. Our results show that urbanization can reduce the importance of introduction pressure in determining alien species richness. Additionally, the results predict that alien species richness will increase at finer spatial scales, especially if the introduced species can survive in urban areas outside of their native range.