The risk of threshold responses, tipping points, and cascading failures in pollination systems

Abstract

Growing evidence of global declines in pollinator abundance and diversity has raised concerns about the resilience of pollination systems. When subjected to stressors, each nested component of the pollination system (communities, populations, and colonies) can respond in either a smooth linear fashion, or in an abrupt nonlinear manner. Threshold and tipping point responses to stress are of particular concern because they result in sudden changes with little warning; such changes may lead to persistent non-functional states that are difficult to reverse. Here, we review evidence for threshold and tipping point responses at the colony, population and community levels of the pollination system. We find that while there are strong theoretical reasons to expect tipping point and threshold responses at all three levels of the pollination system, evidence in the field is lacking for all levels except the colony level. While this is encouraging, caution is still warranted as tipping point and threshold responses—by their very nature—may not be apparent until they are underway. Moreover, we propose that the interaction of nonlinear stress responses across different levels of the pollination system can increase the risk of cascading failures. We therefore suggest a cautious approach toward the management of pollination systems. Since environmental change will almost certainly continue to accelerate, understanding the potential for thresholds, tipping points and cascading failures is key to safeguarding global pollination systems.