Vergleichende Untersuchungen an Alpinen und Nicht-Alpinen Populationen von Larinus Sturnus Schall. (Col.: Curculionidae): Diversität und Produktivität im Ökologischen Grenzbereich

Abstract

A comparative study of Alpine and non-Alpine populations of the weevil species Larinus sturnus Schall. shows a number of morphological (body size, length and width of female rostrum) and biological (larval feeding habits) differences. The pecularities of the Alpine populations can be interpreted as adaptations to the special structure of the capitula of their host plant, the Alpine Thistle (Cirsium spinosissimum (L.) Scop.). The life-system of the Alpine L. sturnus populations is characterized by a single host plant species, a single phytophagous competitor and a single entomophagous enemy, whilst the lowland populations of L. sturnus form part of a complicated system involving several host plants, phytophagous competitors and entomophagous enemies. There is a clear negative correlation between the general diversity of the L. sturnus life-systems, on the one hand, and the frequency and productivity of the weevil species, on the other hand. The biomass production per host plant unit in Alpine L. sturnus populations is often considerably higher than the total production of phytophagous biomass by comparable host plants in non-Alpine L. sturnus life-systems. The Alpine L. sturnus populations demonstrate that an autecologically marginal zone with reduced interspecific competition and enemy pressure may become an optimal zone for ecologically flexible species.