Abstract The conversion of natural lands in urban areas is exponentially increasing worldwide, causing a major decline in biodiversity. Environmental alterations caused by urbanization, such as land conversion and isolation of natural patches, favour tolerant and generalist species, causing both species loss and replacement. In addition, selective pressure is exerted on particular functional traits, driving a functional homogenization or turnover of biotic communities. We sampled ground arthropods within the municipality of Turin (NW-Italy), wherein an isolated and a connected control subplot were repeatedly sampled at 15 stations distributed along a gradient of increasing urbanization. Such a nested sampling design allowed us to investigate the taxonomic and the functional responses of carabids and spiders to both the urbanization level and patch isolation. First, we highlighted the dominant role played by species homogenization (nestedness) in explaining both taxonomic and functional variation in both groups of arthropods. Secondly, we showed that urbanization causes simultaneously functional homogenization and replacement in both carabid and spider assemblages, whereas patch isolation influences carabid species composition and homogenizes and shifts spider taxonomic and functional composition. Lastly, by relating community-weighted means of body length, dispersal capacity and trophic strategy to the urbanization and isolation gradients, we demonstrated that urbanization alters the trophic structure of both taxonomic groups and increases the average dispersal capacity of spiders. On the other hand, patch isolation affected the functional composition of spiders only, reducing the body size and increasing dispersal capacity and the proportion of web-builder species. Our results demonstrate that both urbanization and patch isolation alter species composition by causing functional and taxonomic homogenization. In addition, they exert a strong filtering effect on community functional traits, increasing the proportion of phytophagous species in carabids, and increasing dispersal capacity and web-builders occurrence in spiders, while reducing spider body size.

中文翻译：

---

城市中的岛屿：城市化和碎片化驱动地面节肢动物的分类和功能变化

摘要 世界范围内城市地区自然土地的转化呈指数级增长，导致生物多样性大幅下降。城市化引起的环境改变，例如土地转换和自然斑块的隔离，有利于宽容和通才的物种，导致物种损失和更替。此外，对特定功能性状施加选择压力，推动生物群落的功能同质化或周转。我们对都灵市（意大利西北部）内的地面节肢动物进行了采样，其中一个孤立的和连接的控制子小区在 15 个沿城市化程度增加的梯度分布的站点上重复采样。这种嵌套的抽样设计使我们能够研究carabids 和蜘蛛对城市化水平和斑块隔离的分类和功能反应。首先，我们强调了物种同质化（嵌套）在解释两组节肢动物的分类学和功能变异方面所起的主导作用。其次，我们表明城市化同时导致了carabid和蜘蛛组合的功能同质化和更替，而补丁隔离影响carabid物种组成并使蜘蛛分类和功能组成均质化和变化。最后，通过将社区加权的体长、扩散能力和营养策略与城市化和隔离梯度相关联，我们证明了城市化改变了两个分类群的营养结构并增加了蜘蛛的平均传播能力。另一方面，斑块隔离仅影响蜘蛛的功能组成，减小了体型，增加了散布能力和织网物种的比例。我们的结果表明，城市化和斑块隔离都通过导致功能和分类同质化来改变物种组成。此外，它们对群落功能性状有很强的过滤作用，增加了甲虫中植食性物种的比例，增加了蜘蛛的传播能力和建网者的发生率，同时减少了蜘蛛的体型。斑块隔离仅影响蜘蛛的功能组成，减小了体型，增加了散布能力和织网物种的比例。我们的结果表明，城市化和斑块隔离都通过导致功能和分类同质化来改变物种组成。此外，它们对群落功能性状有很强的过滤作用，增加了甲虫中植食性物种的比例，增加了蜘蛛的传播能力和建网者的发生率，同时减少了蜘蛛的体型。斑块隔离仅影响蜘蛛的功能组成，减小了体型，增加了散布能力和织网物种的比例。我们的结果表明，城市化和斑块隔离都通过导致功能和分类同质化来改变物种组成。此外，它们对群落功能性状有很强的过滤作用，增加了甲虫中植食性物种的比例，增加了蜘蛛的传播能力和建网者的发生率，同时减少了蜘蛛的体型。