A reconstructed Pangea would result in lower biodiversity

Driven by globalization and climatic change, rates of biological invasion are on the increase. Although these increasing rates are widely expected to lead to increased rates of extinction, it has been argued that these ‘newly arrived' species might increase biodiversity. It is also argued that extinction due to non‐native species is only a ‘small island phenomenon', and that species in continental regions are unlikely to be threatened. In this paper we attempt to resolve these paradoxes associated with colonising non‐native species. We introduce a stylized model framework, based on combining the neutral theory of biodiversity with the species–area relationship (SAR), to examine the role of dynamic phenomena. We use this framework to perform a series of ‘thought experiments'. The first considers a ‘Pangea' reconstructed by globalisation; a second considers the union of two islands; and a third considers the effects of climate‐driven invasions. In both thought experiments two and three there can be immediate increases in local biodiversity, but these increases are ephemeral and typically followed by declines. This happens because the biodiversity increases are dynamic processes related to redistributions of species, while subsequent slow declines are closely connected with extinction debt. Thus, increases in species richness caused by colonising non‐native species may be a temporary phenomenon, and not sustainable. Our study helps resolve some paradoxes, regarding the effects of exotic species, and may contribute to improving guidelines for conservation and management.