Recently, several authors have claimed that the sexual reproduction of many plant species is threatened by declining pollinator frequencies because of human impact (Allen-Wardell et al., 1998; Kearns et al., 1998; Karrenberg & Jensen, 2000). Although various butterfly species visit D. carthusianorum in the investigated population, a decline in abundance, or a loss of one or even both of the two main pollinator species, could cause a serious threat to the local persistence of D. carthusianorum. Such a threat is realistic as both species, although locally abundant, are generally rare, weak dispersers, and are restricted to the ecological conditions of the local environment of rocky steppes (Benz et al., 1994), itself a rare, species-rich habitat drastically reduced by viticulture, housing development and fertilization (Delarze et al., 1999). In the Rhone valley of south-eastern Switzerland both butterfly species, M. galathea and S. ferula, have vanished from 29 of 67 and 31 of 62 sites, respectively, since 1970 (Gonseth, 1987). Thus the population density of both pollinator species shows a tendency to collapse or to go locally extinct. Furthermore, the observed pollinator limitation does not suggest that pollinator species compete significantly for nectar in D. carthusianorum. It therefore seems unlikely that the remaining pollinator species could compensate for a decrease in the primary pollinator species. However, as D. carthusianorum is self-compatible (no apomixis), a minimal sexual reproduction could be assured by selfing, although pollen quantity deposited by selfing is precariously close to the threshold for fruit formation. Thus the risk of local extinction will eventually depend on the demographic consequences of inbreeding (Schemske, 1983; Waser, 1983; Waser & Price, 1983; Bond, 1995). Furthermore, flight distances of pollinators between visited flowers affect the progeny's fitness (Price & Waser, 1979; Levin, 1981). Butterflies cover greater flight distances than other insects, and therefore are able to sustain a higher effective population size (Beattie & Culver, 1979; Schmitt, 1980). Hence a stronger inbreeding depression is likely if a plant population becomes dependent on selfing because of a lack of pollinators. Consequently, D. carthusianorum may face serious inbreeding depression in the case of decreasing pollinator abundances. Other impacts of human activities, whether habitat deterioration or destruction and fragmentation (Jennersten, 1988), further threaten this plant–pollinator system.