INVERTEBRATE SUCCESSION ON AN ALPINE GLACIER FORELAND

Abstract

Since there is little known about invertebrates in glacier foreland succession, the aim of this study was (1) to characterize succession patterns of the epigean fauna, (2) to analyze how these are related to plant succession, and (3) to investigate the influence of locally varying environmental conditions. The Central Alpine glacier foreland of the Rotmoostal (Obergurgl, Tyrol, Austria) was selected as an example situated above the treeline (2280–2450 m above sea level) where a 2 km long deglaciated area covers a chronosequence of 140 yr. The epigean fauna was sampled in 70 plots of all ages and in nearby sites outside the foreland by pitfall trapping over the entire growing season in 1996 (June–October). Abiotic characterization and vegetation recordings were available for all plots. Rapid development of pioneer communities over 50 yr was followed by little change in older stages. Further development towards the mature invertebrate communities characteristic of areas outside the foreland only occurred on the sunny slopes near the terminal moraine and proceeded in a qualitatively different way. Sites in the alluvial outwash plain or otherwise physically disturbed were clearly successionally younger than adjacent undisturbed sites. The first colonizers were almost exclusively predators. Herbivores and decomposers appeared later. Similarities and differences between faunal and floral succession patterns are discussed. The major factors affecting faunal succession as identified by canonical correspondence analysis were soil formation and vegetation development along the chronosequence. In addition, favorable sun and light conditions may facilitate successional progress. Fauna communities also react to local conditions, most notably to the moisture/snow cover regime. Abiotic environment, architecture of plants, and plant species composition interact strongly as explanatory factors, but all three aspects also contribute significant unique correlations. There were no hints of random colonization patterns at the youngest sites. Pioneer invertebrate communities had the same small-scale spatial heterogeneity and equally strong correlations with environmental conditions as did the well-established communities at older sites. This leads to the conclusion that faunal colonization and succession in Alpine glacier forelands, to a large extent, follow predictable and deterministic assembly rules and that stochastic effects are of minor importance.