Trophische Beziehungen in einem Küstendünen-Ökosystem, Einer „Natürlichen Monokultur“ von Ammophila Arenaria

Abstract

The regulating influence of predators on the density of phytophagous insects in pure stands of Ammophila arenaria was studied on coastal dunes at the Baltic Sea. Dominant phytophagous insects were ectophagous Heteroptera, Homoptera, Coleoptera and endophagous Diptera with a biomass of 0.11–0.14 g/m² (dry weight) in 1975 according to season. The biomass of the zoophagous arthropods (mainly Araneida, Heteroptera, Carabidae, Staphylinidae, Coccinellidae) amounted to 0.31–0.52 g/m². Saprophagous arthropods were represented only in low density (0.05–0.07 g/m²). According to a rough estimate the predators consumed at least 0.02 g prey/m² and day (with a maximal proportion of 40% phytophagous arthropods). Most phytophagous species (except some Heteroptera, Coleoptera) were taken as prey. Parasitism of the herbivores by entomophagous insects (mainly Hymenoptera) was not important. Catches with sticky traps demonstrated that predators were active in the whole spatial structure of A. arenaria.

In experimental plots the predators were partly eliminated by parathion or hand in September 1975. In the following spring and summer the density of phytophagous insects increased significantly when compared with untreated control plots. After addition of predators to experimental plots in spring 1976 the density of herbivores was not lowered significantly.

Probably the general predators are capable of limiting the density of the herbivores and are — among other factors (e.g. climate, resistance of Ammophila) — responsible for the fact that no gradations of phytophagous insects develop in the coastal dunes, a „natural monoculture“ of Ammophila arenaria.