Buzhdygan O. Assessment of the mechanisms of deterioration in ecosystem functioning using ENA- and SEM-modelling

In the current work we applied the promising tools of the Structural Equation Modelling (SEM) and of the Ecological Network Analysis (ENA) to assess the mechanisms of altered structure and functions of the terrestrial and aquatic ecosystems under the effects of anthropogenic pressure, biodiversity loss and invasive colonization of plant community. We constructed the cause-effect SEM models for the biocommunities of the grassland ecosystems along the gradient of grazing intensity as well as for the pond ecosystems along the gradient of anthropogenic-impact intensity. Based on the SEM models we found direct and indirect effects of human-impact intensification mediated via altered habitat or trophic interactions on species richness and abundance within each trophic level as well as for the entire multitrophic community. We performed the comparative analysis of the sensitivity among the trophic groups of biota to the effects of anthropogenic pressure. The observed mechanisms underlying the effects of human-impact intensity on species richness and abundance of the trophic groups across the ecosystem might be important for the understanding of the cause-effect relationships among the ecosystem functioning and human activities in grasslands and ponds. In the study we assembled the trophic models of the energy dynamics using ENA for the experimental grassland ecosystems along plant species richness gradient. We estimated the following emergent ecosystem properties for each study system: total biomass storage in the trophic network, total energy flow through the system, relative energy losses (energetic efficiency of the ecosystem), and flow centrality (distribution of resources across the trophic network). The directions and strengths of the plant diversity effects on the emergent ecosystem functions were assessed in the study grasslands. Further, we constructed the ENA models of the nitrogen cycle in the floodplain ecosystems undergoing the invasive colonization by Robinia pseudoacacia L. and for the floodplain ecosystems of the native species Salix alba L. This allowed us to distinguish the mechanisms underlying the changes in the following emergent ecosystem properties in the colonized floodplains compared to the native species: total standing stock of nitrogen, total nitrogen flow through the ecosystem, and nitrogen storage efficiency.