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

Young climbers successfully avoid predators: survival behavioural strategy of juveniles of the land snail Ezohelix gainesi

Predation risk has a great influence on animal behaviour. Juveniles are often more susceptible to predation than adults owing to their small body size and limited locomotive ability. Ezohelix gainesi (Camaenidae) is a ground-dwelling land snail that swings its shell as a strategy to avoid predation by beetles. This strategy, however, does not seem to work in juveniles, probably because of their small shell size. Instead, small individuals climb plants as an alternative strategy that is likely to avoid predation; to examine this, we initially made an experimental comparison of the rates of predation by beetles on land snails of different sizes. In these conditions, smaller snails were preyed upon more frequently than larger ones. Next, we compared the size distribution of snails on plants with those on the forest floor. Small snails occurred more frequently on plants than on the ground, and the shell diameter of land snails at 50% probability of occurring on plants was similar to that at 50% probability of predation. Climbing behaviour by small snails was also confirmed in the laboratory in the absence of predators. Therefore, plant-climbing by juvenile E. gainesi is probably an adaptive strategy to avoid predation by ground-dwelling beetles.

Land snail assemblages and microhabitat preferences in the urban areas of Kolkata, India

Due to the minimal dispersal capabilities and dependency on particular microhabitat, the land snails are susceptible to anthropogenic and natural disturbances. Considering the increasing anthropogenic threats, especially in urban areas, information on species’ requirements for particular habitat is very essential for land snail conservation and sustenance. In the present commentary, diversity and distribution of small-sized land snails in relation to their microhabitat preference in urban habitats of Kolkata, West Bengal, had been carried out through the quadrat method. The information on the richness and abundance of snails and their habitat places in Kolkata, India, was used to construct a bipartite network. A total of 13 land snail species were linked with 16 microhabitats. The network indices were used to justify the specialist or generalist nature of the snail species in the context of microhabitat preference. The snail species Succinea daucina and Allopeas gracile were observed to be associated with the maximum number of habitats while species strength was highest for S. daucina. The low value of connectance (0.288, <0.5) and niche overlap (0.34), the high value of specialization index H2′ (0.58) and d′ (0.44) indicate that the snail–microhabitat interactions were highly specialized. The network ecology of snail–microhabitats illustrated in the present instance will enable the identification of preferred microhabitats, which are required for the enhancement of the population of land snails in urban areas like Kolkata, India.