The mechanistic basis of changes in community assembly in relation to anthropogenic disturbance and productivity

Abstract

In the human-dominated world the natural drivers of species diversity, such as productivity and habitat heterogeneity, have been accompanied by anthropogenic disturbance resulting in increased extinction rates at global scale. However, decrease in species richness does not necessarily result in local decreases in species richness. Moreover, species richness provides limited information on processes that cause changes within and between communities, and the mechanistic basis of these changes remains elusive. As all patterns in community ecology can be understood as a result of four processes (speciation, selection, drift, and dispersal), the effect of disturbance should depend on how disturbance disrupt these processes. We studied the effects of disturbance and productivity on species richness, community composition, and beta diversity (i.e. spatial variation in community composition) in the vegetation of 120 boreal peatlands. Using null model approach we determined whether community assembly processes differ between pristine and disturbed sites. Sites represented three peatland ecosystem types, each with two levels of productivity. Half of the sites were pristine and half were drained for forestry, which causes a major ecosystem level disturbance. Our results showed that high productivity sites encompassed higher species richness and different communities than low productivity sites. By contrast, we did not observe any difference in beta diversity between high and low productivity sites. Between pristine and drained sites neither species richness and nor beta diversity differed. Instead, peatland communities in drained were dissimilar to pristine sites, thus showing changes not attributed to drift but to selection, most likely based on altered hydrology, pH, and nutrient gradients. Moreover, the changes due to drainage were toward forest communities which could lead to landscape level homogenization. Effective ways to combine knowledge of the landscape level changes among disturbed areas and the understanding of the mechanisms affecting communities locally are important for reaching the ambitious global targets of restoring the degraded ecosystems. 1. Elo et al. (2016) The mechanistic basis of changes in community assembly in relation to anthropogenic disturbance and productivity. Ecosphere 7: e01310