Structure-dynamic relationship of plant–insect networks along a primary succession gradient on a glacier foreland

There is a growing interest in understanding the structure–dynamic relationship of ecological networks.Ecological network changes along primary successions are poorly known: to address such topic, gradientof primary succession on glacier forelands is an ideal model, as sites of different age since deglaciationstand for different ecosystem developmental stages. We aimed to investigate the assembly processesof plant–insect networks and to elucidate its functional implications for ecosystem stability along thistime sequence succession. We collected data on the functional role of anthophilous insect groups andperformed network analysis to evaluate their relative importance in the structure of plant–insect inter-action networks with increasing time since deglaciation along the primary succession of a debris-coveredglacier foreland. We sampled anthophilous insects visiting the flowers of two models plant species, Leu-canthemopsis alpina and Saxifraga bryoides. Insects were identified and trophic roles were attributed toeach taxon (detritivores, parasitoids, phytophagous, pollinators, predators, and opportunists) at five sitesrepresenting the primary succession gradient. Plant–insect interactions were visually represented by abipartite network for each successional stage. For each plant species and insect group, centrality indiceswere computed quantifying their community importance. For the whole network, centralization and linkdensity were calculated. Pollinators dominated pioneer communities on the debris-covered glacier andin recently deglaciated areas, while parasitoids, predators and opportunists characterised late-successionstages. Plant species centrality varied along the succession. Pollinators showed initially higher but thendecreasing centrality, while the centrality of predators and parasitoids increased with time since deglacia-tion. Along the same gradient link density showed an increasing trend while network centralizationtended to decrease. The present study provides new insight into the initial steps of plant–insect networkassembly and sheds light on the relationship between structure and dynamic in ecological networks. Inparticular, during the succession process, more links are formed and plant–anthophilous insect interac-tions change from a network dominated by pollinators to a functionally more diversified food web. Weconclude that applying network theory to the study of primary succession provides a useful frameworkto investigate the relationship between community structure and ecosystem stability.