Insect and arachnid colonization on the Storbreen glacier foreland,Jotunheimen,Norway: Persistence of taxa suggests an alternative model of succession

Abstract

This article investigates colonization patterns of invertebrates on recently deglaciated terrain (Storbreen, Jotunheimen, Norway) and their implications for primary succession theory. Taxa were collected using 243 pitfall traps across a 250 yr chronosequence of six age zones. Distribution and abundance were analysed, communities were mapped, classified using TWINSPAN (Two-Way INdicator SPecies ANalysis), and ordinated using NMS (Non-metric Multidimensional Scaling). Thirty-one of the 72 recorded taxa colonised terrain deglaciated within 20 years, some carnivorous taxa and vagrants preceding the establishment of vegetation. Most taxa persisted during succession with little or no evidence of replacement change for the first 150 years. Taxa continued to accumulate throughout the succession but most reached maximum abundance after 62–152 years. The change in dynamics after 152 years is attributed to increased competition between invertebrate taxa rather than a response to vegetation succession. Insect communities on the glacier foreland are interpreted as a continuum of variability: six weak communities identified within 20 years of deglaciation develop within 150 years into two loose communities of persistent taxa. The colonization process can be appropriately described as an ‘addition’ rather than ‘succession’, while persistence of taxa rather than replacement change provides the basis of an alternative model of insect succession.