Contrasting effects of urbanization on arboreal and ground-dwelling land snails: role of trophic interactions and habitat fragmentation

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.

Harnessing soil biodiversity to promote human health in cities

“…Also, diversity losses of macroinvertebrates in cities may increase CO 2 emissions through reduced carbon and nitrogen sequestration due to reduced litter decomposition and incorporation into the soil [40][41][42] . Further, the loss of top predators (e.g., birds of prey) and altered habitat characteristics in urban ecosystems can result in functionally destabilised food-webs (including those in soil) and result in changes to trophic cascades that benefit certain soil biota groups, including termites, ants and snails that risk damaging buildings, reducing plant performance and transmitting human pathogens [43][44][45][46] . As ecosystem health is intimately tied to human health through the provisioning of ecosystem services 47 , changes in soil biodiversity will ultimately translate to human health impacts 48 .…”

The potential and practice of arboreal camera trapping

“…Dalloz et al, 2012;Laughlin et al, 2017;Mella et al, 2018) and interspecific interactions (e.g. Saeki et al, 2020;Schruhl et al, 2012;Zhu et al, 2021) that would otherwise be difficult to observe in the et al, 2019). Additionally, this method has been used to evaluate the effectiveness of crossing structures intended to mitigate the barriers of linear infrastructure (e.g.…”

“…Dalloz et al., 2012; Laughlin et al., 2017; Mella et al., 2018) and interspecific interactions (e.g. Saeki et al., 2020; Schruhl et al., 2012; Zhu et al., 2021) that would otherwise be difficult to observe in the canopy. For example, cameras placed in the Ankeniheny–Zahamena rainforest corridor in eastern Madagascar validated the presence of the critically endangered greater bamboo lemur Prolemur simus (Olson et al., 2012), and the first documentation of the pollinator community of the endangered and epiphytic ghost orchid Dendrophylax lindenii in Florida's Everglades Basin was made by cameras (Houlihan et al., 2019).…”

“…Dalloz et al, 2012;Laughlin et al, 2017;Mella et al, 2018) and interspecific interactions (e.g. Saeki et al, 2020;Schruhl et al, 2012;Zhu et al, 2021) that would otherwise be difficult to observe in the (Olson et al, 2012), and the first documentation of the pollinator community of the endangered and epiphytic ghost orchid Dendrophylax lindenii in Florida's Everglades Basin was made by cameras (Houlihan et al, 2019). Additionally, this method has been used to evaluate the effectiveness of crossing structures intended to mitigate the barriers of linear infrastructure (e.g.…”