Loop analysis quantifying human impact in a river ecosystem model

Abstract

In ecological systems, multiple interactions connect various kinds of components. Strong and weak as well as positive and negative effects cause complex dynamics and often quite unpredictable processes. Human impact is added to this complexity, with all of its diverse effects. In this paper, we present a case study on the Kelian river ecosystem (Borneo), connecting pristine habitats upstream, a gold mine close to the middle section and human settlements downstream. For six locations, separate food web models had been developed earlier. Here we first analyze the ecological system by loop analysis and compare its outcome for different sites. Second, we identify the most crucial human impacts and implement these in modified loop analysis models. We determine the sign of various effects and study the consistency of human impact on different sites and various organisms. Adding human impact to the models (1) increased the ratio of clear predictions, (2) caused the appearance of “zero” predictions in three sites and (3) reduced the variability of predictability along the river.