Urbanization generally reduces wildlife populations. Individual species responses, however, are often highly variable, and such variability can be explained by differences in species ecological traits. To examine this hypothesis, we focused on two co-occurring land snails, Ezohelix gainesi and Euhadra brandtii sapporo; the former is ground-dwelling and the latter is arboreal. We first estimated their population densities at nine sites distributed along an urbanization gradient: three were located in continuous natural forests, three at the edge of natural forests, and the rest in small isolated forests in urban areas. As a result, the ground-dwelling E. gainesi occurred at highest density in urban forests, followed by forest edges and continuous forests. By contrast, the arboreal E. b. sapporo occurred at highest density in continuous forests, but declined in forest edges and urban forests. We then conducted manipulative field experiments to quantify changes in predation pressure on these species. Ground-tethered E. gainesi and E. b. sapporo were repeatedly predated upon by forest-living mammals in continuous forests, but their survival rates increased in forest edges and urban forests. By contrast, canopy-tethered E. b. sapporo maintained high survival rates in all three forest types. The results indicate that a lack of mammalian predators enables ground-dwelling species to occur at high densities in urban forests, whereas the arboreal species was not affected by this predator relaxation effect. The combination of species-specific behavioural traits and changes in predator communities across an urbanization gradient has important effects on the biodiversity of urban ecosystems.

中文翻译：

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城市化对树木和栖地蜗牛的影响：营养相互作用和生境破碎化的作用

城市化通常会减少野生动植物的数量。但是，单个物种的反应通常是高度可变的，而这种可变性可以通过物种生态特征的差异来解释。为了检验这一假设，我们集中研究了两种同时发生的蜗牛，即埃佐海利克斯·埃涅西（Ezohelix gainesi）和Euhadra brandtii札幌；前者是住宅，后者是树木。我们首先在沿城市化梯度分布的九个地点估算了它们的人口密度：三个地点位于连续的天然林中，三个地点位于天然林的边缘，其余地点位于市区的小片孤立森林中。结果，居住在地面上的E. gainesi发生在城市森林中密度最高的地方，其次是森林边缘和连续森林。相比之下，树栖植物E．札幌在连续森林中以最高密度发生，但在森林边缘和城市森林中下降。然后，我们进行了操纵性野外实验，以量化这些物种的捕食压力变化。地面束缚的E. gainesi和E. b。在连续森林中，居住在森林中的哺乳动物反复捕食札幌，但在森林边缘和城市森林中，它们的成活率有所提高。相比之下，树冠拴住的E. b。札幌在所有三种森林类型中均保持较高的成活率。结果表明，缺乏哺乳动物的捕食者使得居住在地面上的物种能够以高密度出现在城市森林中，而树栖物种不受这种捕食者放松效应的影响。特定物种的行为特征与整个城市化梯度中捕食者群落的变化相结合，对城市生态系统的生物多样性具有重要影响。