Invasion of a Crimean land snail Brephulopsis cylindrica into protected relict steppic hilltops (tovtrs) in Western Ukraine: a threat to native biodiversity?

Abstract

Brephulopsis cylindrica (Menke 1828), a snail native to the Crimea, has been expanding northward and westward, and has recently reached Western Ukraine. Three adjacent and abundant colonies have been found in the tovtrs (small rocky hilltop areas of protected relic steppic habitat) of the Podilski Tovtry National Nature Park in Western Ukraine. These sites and ten similar sites without B. cylindrica were sampled. Most of the snail species that occur in the other ten sites were absent from the samples from the sites with B. cylindrica, which have much lower molluscan diversity. It is suggested that B. cylindrica is excluding some threatened native snails that have comparable ecological preferences, notably Helicopsis striata. Possible mechanisms of competition with native species are discussed. The most likely explanation is that these native snails are displaced from seasonal refuges in rock crevices as a result of the high densities of B. cylindrica. The snails in Western Ukrainian populations of B. cylindrica are smaller than in populations from the Crimean mountains, but similar in size to populations from the Crimean plains, which may be where they originated.