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

Abstract

Anthropogenic disturbance often causes changes in communities. However, 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 community dispersion (i.e., variation in community composition) in the vegetation of 120 boreal peatlands using null-model approach to determine 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 disturbed by drainage and half are pristine. Pristine and disturbed sites showed similar species richness. However, their community composition differed indicating a directional selection due to disturbance, whereas dispersion of disturbed and pristine communities did not differ suggesting no change in the relative strength of selection and drift. Our results suggest that understanding the combination of landscape level community changes and local selection pressures is important when restoration of degraded ecosystems is undertaken.