Diversity Over Time

Temporal turnover is a fundamental feature of ecological communities. Darwin 1859 noted the ecological and evolutionary significance of turnover, Fisher and Preston acknowledged its role in their models of species abundance, while this ongoing and entirely natural rearrangement of species underpins key ecological concepts such as MacArthur and Wilson's theory of island biogeography. However, the current focus on spatial patterns of diversity means that temporal changes are often overlooked. Here I argue that failure to take heed of the time frame over which data are collected can lead to both artefacts and artifictions. There are also deeper issues, such as the consequences for species richness estimation and rarefaction methods of a constantly changing community. Moreover, some of the confusion surrounding species abundance distributions may be resolved by taking account of time. A better appreciation of temporal turnover is essential for accurate diversity measurement and assessment, and, more importantly, will also lead to improved understanding of the processes that underpin community structure.