Once a land of big wild rivers: specialism is context-dependent for riparian snails (Pulmonata: Valloniidae) in central Europe

Abstract

Specialist species may be perceived as such because of their narrow ecological requirements, but this may be context‐dependent. The genus Vallonia (Gastropoda Pulmonata: Valloniidae) includes widespread generalist species and also two specialists endemic to Central Europe: Vallonia suevica, restricted to warm, wet meadows and riverbanks subject to seasonal flooding; and Vallonia declivis, living only in wet to humid meadows, riverbanks, and reedbeds. Both have experienced dramatic declines; as is the case with many land snails, their global conservation status has been underestimated: these species are Critically Endangered. Other congenerics are probably dispersed by birds. In contrast, the distributions of these meadow specialists appear to be the outcome of their strictly riparian habitat coupled with dispersal by fish. Thus, they have tracked drainage changes through the Pleistocene from their origin in the floodplain uplands of the Danube biodiversity hotspot in the Pliocene. Natural dispersal mechanisms have been disrupted, and riparian and river ecosystems have been destroyed throughout Europe. This has led big‐river specialist molluscs and their associated fishes to the brink of extinction. The notion of specialism thus depends on the ecological context; it is useful to stress their non‐invasive character, current restriction to scarce habitats, and evolution under quite different conditions. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, ●●, ●●–●●.

Comment on Altaba (2015): a case of species misidentification?

“…Previously in this journal, Altaba () presented an original hypothesis on the dispersal of small wetland snails in Central Europe after the Last Glacial Maximum, based on the discovery of rare species of the genus Vallonia at the foot of the Devín Hill, facing the confluence of the Morava and Danube Rivers, in Slovakia on the borders with Austria. Given the occurrence of these species in rivers further north, he suggested that the patterns of distribution could be explained by the transport of these snails by fish.…”

“…Although such transport is well‐attested for the glochidia larvae of unionid bivalves, it has never been directly recorded for terrestrial snails. Nevertheless, improbable as such a dispersal mechanism might appear, the pattern of distribution shown in Altaba () is certainly not incompatible with it, and it raises many questions about the dispersal of land snails in this region.…”

“…His paper included excellent, scaled photographic images of the rare species concerned (Altaba, : fig. 2).…”

“…2). Examination of these images, however, clearly indicated that these specimens were very likely misidentified, and that those shown actually belong to the common and widespread species Vallonia pulchella , although one might plausibly be assigned to the equally widespread Vallonia excentrica (Altaba, : fig. 2, the second specimen from the top).…”

Restoration of a Danube floodplain forest: what happens to species richness of terrestrial beetles?

“…In the context of the program MONDAU, we surveyed a part of the local fauna. In contrast to recent faunistic floodplain studies, where most attention was paid to birds (Hatten & Paradzick ; Utschick et al, ), fish (Lasne et al, ; Pander et al, ), mollusks (Cejka & Hamerlik ; Horackova et al ; Altaba ), amphibians (Ponsero & Joly ), and aquatic invertebrates (Bunn & Arthington ), we focused on the biodiversity of beetles living terrestrially. Beetles colonize almost all ecological niches (Gomez‐Rodriguez et al ) and they are represented in Germany by ca.…”