Understanding pathways to environmental sustainability in tropical regions is a priority for conservation and development policies. Because drivers of environmental degradation often occur simultaneously, a holistic approach is needed. We analyzed environmental degradation on demarcated indigenous lands in Guyana, using a spatially explicit, agent‐based simulation model representing human livelihoods, forest dynamics, and animal metapopulations. We examined four plausible drivers of ecological degradation: conversion of land for agro–industrial use, erosion of hunting and dietary taboos, reduction in child mortality rates, and introduction of external food resources. Although social–ecological systems were resilient to internal changes, the introduction of external food resources resulted in large fluctuations in the system, leading to a deterioration in environmental sustainability. Our simulation model also revealed unexpected linkages within the system; for example, population growth rates of non‐human animal species were related to the sustainability of human livelihoods. We highlight the value of simulation models as social–ecological experiments that can synthesize interdisciplinary knowledge bases and support policy development.