Arthropod food-web development during early stages of primary succession

Primary succession on bare ground surrounded by intact ecosystems e.g. after volcano eruptions or glacier retreat is, during its first stages, characterized by a predator-dominated arthropod community. The absence of herbivores as obvious prey stimulated research on which food sources might sustain those first colonizers. By applying molecular methods, we were able to track the trophic interactions in these early communities in an unprecedented resolution. A total of 1832 predatory arthropods (carabid beetles, lycosid and linyphiid spiders) collected in early and late pioneer stages of three glacier forelands were tested for recent consumption of 19 different prey taxa. The investigated interactions included intraguild predation (predators feeding on each other), collembolans (other early colonizers) and different taxa of flying insects that could actively visit the pioneer stages or be passively blown there by the wind. Albeit the overall situation of food scarcity, which might imply a 'take what you can get' feeding strategy, the predators were found to occupy distinct trophic niches. Semi-quantitative food-webs were established based on predator abundance and detection frequencies of the various prey types. The analysis of these webs showed that general food-web metrics such as connectance, generality and vulnerability increased in all valleys from the early to the late pioneer stage, indicating an increase in the complexity of feeding interactions during primary succession.