Novel communities are a risky business

As in business, most action in biodiversity happens in turnover. Net changes in balance give us some indication of performance. However, knowing the volumes of income and payments that make up that balance conveys much more information about how a business is operating. The same is true of ecological communities: Knowing net changes in the number of species is useful, but the gains and losses of species encapsulated in turnover hold essential information about biodiversity change. High turnover is emerging as the signature of biodiversity patterns in the Anthropocene (1–3), raising questions as to the causes and consequences of high turnover in biodiversity. On page 220 of this issue, Pandolfi et al. (4) look into the deeper past to identify when turnover is so increased that it results in completely new combinations of species, known as novel communities.