When Do Ecosystem Services Depend on Rare Species?

Conservation aims to preserve species and ecosystem services. If rare species contribute little to ecosystem services, yet are those most in need of preservation, tradeoffs may exist for these contrasting objectives. However, little attention has focused on identifying how, when, and where rare species contribute to ecosystem services and at what scales. Here, we review distinct ways that ecosystem services can positively depend on the presence, abundance, disproportionate contribution or, counterintuitively, the scarcity of rare species. By contrast, ecosystem services are less likely to depend on rare species that do not have a unique role in any service or become abundant enough to contribute substantially. We propose a research agenda to identify when rare species may contribute significantly to services.