Abstract
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.
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Change history
03 March 2020
The original version of the article unfortunately contained mistakes in the legends of Fig. 3. The legends (1) Blue square: <Emphasis Type="Italic">Euhadra brandtii sapporo</Emphasis>, ground is changed to Blue square: <Emphasis Type="Italic">Euhadra brandtii sapporo</Emphasis>, canopy (2) Red circle: <Emphasis Type="Italic">Euhadra brandtii sapporo</Emphasis>, canopy is changed to Red circle: <Emphasis Type="Italic">Euhadra brandtii sapporo</Emphasis>, ground.
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Acknowledgments
We sincerely thank Dr. T. Nakaji, Dr. H. Ishii, Dr. K. Nakai, Dr. A. Agetsuma, Dr. O. Kishida, Dr. Y. Okuzaki, Ms. R. Uchida, Mr. J. Uchida, Mr. A. Okuda, Mr. Y. Sasabe, Mr. W. Mukaimine, and staff members of the Tomakomai city government, the Hokkaido Prefectural government, and the Nihon-seishi Corporation for their support. This research was funded by the Japan Society for Promotion of Sciences (grant no. 17 K07270).
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IS, SN, and NO designed research, collected and analysed data, and wrote the manuscript. WA and TH collected data and revised the manuscript. All authors contributed critically the drafts and gave final approval for publication
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Saeki, I., Niwa, S., Osada, N. et al. Contrasting effects of urbanization on arboreal and ground-dwelling land snails: role of trophic interactions and habitat fragmentation. Urban Ecosyst 23, 603–614 (2020). https://doi.org/10.1007/s11252-020-00930-6
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DOI: https://doi.org/10.1007/s11252-020-00930-6