The HANDY model with non-renewable resources and societal effects

RESUMO

We present an extension of the single-population Human and Nature Dynamics (HANDY) model that explicitly incorporates non-renewable resources and societal effects. The model is formulated as a system of four differential equations for which we provide a faithful discrete integrator. In the model, resource extraction and conversion is described by realistic Holling-type functional responses that capture saturation effects for both renewable and non-renewable resources, while efficiency losses are introduced to describe inherent waste. We derive analytic conditions on the model parameters, needed to ensure stable (and sustainable) equilibria, despite population growth and depletion of resources. The different dynamical scenarios that appear in this analysis and the parametric conditions that lead to them, are illustrated by extensive numerical simulations. The societal effects we investigate include adjustable extraction and consumption rates of the resources, alongside a population-driven degradation of Nature and of its regenerative capacity. One immediate conclusion is that permanent environmental damage inevitably precipitates population collapse. In contrast, we also show that the possibility of recoverable capacities, even delayed, may lead to long-term survival and that timely late-stage interventions often succeed in averting extinction entirely.