Summary1. Land snail dispersal abilities are considered poor; however, the current invasion of the French Mediterranean region by Xeropicta derbentina (Krynicki 1836), as well as the past invasions of this region by several other species, seems to contradict this view. 2. Using a multilevel approach, from individual experimentation to landscape analysis, the dispersal abilities and mechanisms allowing the passive dispersal of X. derbentina are studied. 3. The colonization of Provence occurred by stratified diffusion, where short-range active dispersal occurs side by side with long-range passive dispersal. 4. Active dispersal is not as limited as previously thought. In the field, the capturemark-recapture method recorded a maximum distance covered of 42 m in 6 months within a radius of 38 m from the original release point. 5. Temperature and humidity, and therefore the time of year, influence the main type of dispersal. Dispersal is active during wet periods and essentially passive in dry and hot months. 6. Heat avoidance behaviour is one of the mechanisms allowing passive dispersal. 7. Passive dispersal via human activities is the main determinant of X. derbentina distribution within the landscape. In comparison to other species, X. derbentina is found more often in the vicinity of a communication route. 8. These results show that land snails can cover large distances in a lifetime. The potential for active and passive dispersal described in this paper enables X. derbentina to be a successful invasive species and explains the rapid spread and current distribution of this species.
The aim of the study was to assess the impact of a pastoral management chosen to limit the recent expansion of woodland on a Mediterranean mountain on land snail diversity. An additional aim was to acquire quantitative data that could be used to identify pasture environments from Holocene molluscan assemblages. The work was undertaken at the Luberon mountain, Provence, south of France. We used a stratified quantitative sampling scheme according to altitude and vegetation structure. A total of 80 sites were studied. Large species were collected within a 5 × 5-m plot. Small species were extracted from litter and surface soil. A standard procedure for site description was used based on 35 environmental variables. Grazing pressure was estimated according to the impact of grazing on the herb layer. Correspondence analysis and canonical correspondence analysis were performed using canoco 4.0 software. The distribution of land snails is related to altitude and grazing intensity. Large patches of grazed grassland harbour open country and mountain snail species. Thermophilic open ground species are located in grazed grasslands at lower altitude. Shade-loving species are present in ungrazed scrublands or in small clearings on the upper slopes. The lowest species richness, diversity and equitability are associated with large patches of grazed grassland, the presence of a continuous cover of short grass reinforcing this negative impact on snail diversity. Our study is consistent with similar works on land snails or other invertebrates but discordant with vegetation studies. A homogeneous grazed herb layer significantly reduces snail diversity and abundance. Heterogeneity seems to favour snail diversity both at the local and landscape scales. However, sheep grazing contributes to the expansion of suitable habitats for rare snail species.
Xeropicta derbentina is a recently introduced land snail in Provence, France. The present work aims at describing the habitats and the land snail communities that it has invaded. Also, its impact on the species richness and diversity of indigenous communities is assessed. Two areas have been studied in order to cover the range of conditions that X. derbentina is encountering within its current French distribution. Sixty‐five samples were analysed from the most Mediterranean site, Auriol, and 140 from a northern site, Craus de St‐Michel‐l’Observatoire. From these samples, X. derbentina is found to be a thermophilous open‐land species mostly inhabiting human‐impacted habitats. It occurs in large populations (more than 100 individuals collected in 15 min) in habitat characterizing the first stages of secondary successions, from cultivated crops to dense fallow lands. However, within a heterogeneous landscape and if enough time has allowed its dispersal, X. derbentina can be found in almost any kinds of habitat, such as garrigues and woodlands. Consequently, X. derbentina occurs in diverse land snail communities. At the local scale, its large populations could result in a significant decrease in species richness and diversity. At the regional scale, however, the introduction of X. derbentina seems to have increased land snail species richness.
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