Contrasting effects of urbanization on arboreal and ground-dwelling land snails: role of trophic interactions and habitat fragmentation
Contrasting effects of urbanization on arboreal and ground-dwelling land snails: role of trophic interactions and habitat fragmentation
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DOI：
10.1007/s11252-020-00930-6
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发表时间：
2020-02
期刊：
影响因子：
2.9
通讯作者：
I. Saeki;S. Niwa;N. Osada;W. Azuma;T. Hiura
中科院分区：
文献类型：
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作者：
I. Saeki;S. Niwa;N. Osada;W. Azuma;T. Hiura
城市化通常会减少野生动物的数量。然而，个别物种的反应往往是高度可变的，这种可变性可以解释为物种生态性状的差异。为了检验这一假设，我们集中在两个共同发生的土地蜗牛，Ezohelix gainesiandEuhadra brandtii札幌;前者是地面居住，后者是树栖。我们首先估计了它们在沿着城市化梯度分布的9个地点的人口密度：3个位于连续的天然森林中，3个位于天然森林的边缘，其余的位于城市地区的小型孤立森林中。因此，地面居住。gainesi发生密度最高的城市森林，其次是林缘和连续森林。相比之下，树。B. sapporo在连续林中的发生密度最高，而在林缘和城市森林中则有所下降。然后，我们进行了操纵现场实验，以量化这些物种的捕食压力的变化。地面束缚E. gainesiandE. B.在连绵的森林中，sapporowere一再被森林哺乳动物捕食，但它们在森林边缘和城市森林中的存活率有所增加。相比之下，树冠束缚E。B.在所有三种森林类型中，sapporo都保持了较高的存活率。结果表明，缺乏哺乳动物的捕食者，使地面居住的物种发生在高密度的城市森林，而树栖物种没有受到这种捕食者放松效应。物种特有的行为特征和捕食者群落在城市化梯度上的变化相结合，对城市生态系统的生物多样性产生重要影响。
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 gainesiandEuhadra 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-dwellingE. gainesioccurred at highest density in urban forests, followed by forest edges and continuous forests. By contrast, the arborealE. b. sapporooccurred 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-tetheredE. gainesiandE. b. sapporowere repeatedly predated upon by forest-living mammals in continuous forests, but their survival rates increased in forest edges and urban forests. By contrast, canopy-tetheredE. b. sapporomaintained 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.