A two concentric circles model incorporating availability of ecosystem services and affordability of humans to clarify the ecological security concept

As human influences on natural ecosystems continue to expand, the utilization of natural resources is approaching a threshold where unsustainability threatens the security of human society. As the challenging tradeoffs between human resource demand, ecological sustainability and the security of human society have become more widely recognized, ecological security issues have received extensive attention. However, despite the emergence of substantial body of scientific research on these broader issues, there is still no broad consensus on the definition of ecological security and how it should be applied to mediate resource use and conservation dilemmas. Across the body of published research in this subject area, the criteria and evaluation methods are often so different that the results of different studies are difficult to compare. In this paper, we propose that ecological security refers to the degree to which the condition of ecosystem can support a certain level of socioeconomic development or quality of life. We propose a simple geometric model to quantify ecological security in two dimensions: the availability of ecosystem services and the affordability of humans. The availability dimension is determined by the supply and demand of ecosystem services and the affordability dimension is determined by the cost and the paying capacity balance to obtain ecosystem services. Then, we applied this model to two hypothetical cases to demonstrate its usefulness. The most important feature of the proposed model is that it enables the quick evaluation of important aspects of ecological security for a study area using eight key factors. Although the shape and geographic characteristics of a study area are usually more complex than the hypothetical case, our model can be applied if the conditions are properly simplified or adjusted.