Conservation of the land snails in the mountain grasslands of the argentinian pampas

DELHEY V.K., BURELA S., PIZÁ J., GHEZZI N.S. & N. J.CAZZANIGA

Tentacle

Año: 2005 p. 11 - 13

0958-5079

Ventania Mountains are a local ‘biodiversity island’ in the Pampas and the most altered region by agricultural activities in Argentina. Both endemic land snails and species of the surrounding plains are present in these mountains. The state park ‘Parque Provincial Ernesto Tornquist’ (PPET) is the only reserve protecting these unique grasslands. Our project aimed to investigate distribution, habitat requirements and potential threatening factors (feral horses and exotic pines) for land snail populations. Another objective was to investigate the effect of environmental conditions and the possible impact of horses on the distribution and abundance of the four most frequent autochthonous macrosnail species. Sampling was carried out at two geographical scales. Environmental conditions recorded included topography, habitat structure, vegetation physiognomy, climatic and edaphic factors, floristic composition and horse impact. The elusive microsnail Zilchogyra franzi Weyrauch 1965 (Helicodiscidae), not recorded since its description and known so far solely by the holotype, is apparently restricted to this particular habitat. Snail species Austroborus lutescens dorbignyi (Doering, 1876) (Strophocheilidae), Discoleus aguirrei (Doering, 1884) (Orthalicidae, Bulimulinae), Plagiodontes patagonicus (d’Orbigny, 1835), and the strictly endemic Ventania avellanedae (Doering, 1881) (Orthalicidae, Odontostominae) commonly co-occurred and they generally presented similar qualitative responses to environmental variables. At microgeographical scale habitat structure variables were the most informative. Notably, presence of rocks seemed to be an important habitat requirement for snails, apparently as a source of shelter Abundance and frequency of snail occurrence across the different environments within the PPET was uneven; some of the responses to ecological variables, including horse impact, could explain this particular distribution pattern. Snail species could be affected differentially by horse impact. We have not found any snail population under long term established pinewoods. Climate, topography, as well as calcium content, pH and other chemical soil variables were not major determinants in explaining land snail distribution pattern. We suggest to design a control plan on feral horse populations, which are not part of the natural fauna of the reserve. Other main threat to the local flora and fauna, including land snails, is the spread of exotic pines, which are currently being controlled.