Global concern about human impact on biological diversity has triggered an intense research agenda on drivers and consequences of biodiversity change in parallel with international policy seeking to conserve biodiversity and associated ecosystem functions. Quantifying the trends in biodiversity is far from trivial, however, as recently documented by meta-analyses, which report little if any net change in local species richness through time. Here, we summarise several limitations of species richness as a metric of biodiversity change and show that the expectation of directional species richness trends under changing conditions is invalid. Instead, we illustrate how a set of species turnover indices provide more information content regarding temporal trends in biodiversity, as they reflect how dominance and identity shift in communities over time. We apply these metrics to three monitoring datasets representing different ecosystem types. In all datasets, nearly complete species turnover occurred, but this was disconnected from any species richness trends. Instead, turnover was strongly influenced by changes in species presence (identities) and dominance (abundances). We further show that these metrics can detect phases of strong compositional shifts in monitoring data and thus identify a different aspect of biodiversity change decoupled from species richness. Synthesis and applications: Temporal trends in species richness are insufficient to capture key changes in biodiversity in changing environments. In fact, reductions in environmental quality can lead to transient increases in species richness if immigration or extinction has different temporal dynamics. Thus, biodiversity monitoring programmes need to go beyond analyses of trends in richness in favour of more meaningful assessments of biodiversity change.
Bibliographical noteFunding Information:
This work was inspired by discussions with monitoring agencies and during workshops at different scientific venues. H.H. acknowledges funding by the Ministry of Science and Culture, State of Lower Saxony, through the projects BEFmate and MarBAS. J.M.C., W.S.H. and S.L. acknowledge the support of the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig funded by the German Research Foundation (FZT 118). The authors thank the Dutch General Directorate for Public Works and Water Management (Rijkswaterstaat) for providing the marine phytoplankton data, and Ronald Bijkerk from Koeman & Bijkerk B.V. for clarifying the phytoplankton analysis and data structure. Funding for the Iowa Lake Monitoring Program dataset was provided by the Iowa Department of Natural Resources to J.A.D. and C.T.F. Terrestrial data were made available through the Nutrient Network, a project funded by DEB-0741952 (E. Borer/E. Seabloom) and funded at the site-scale by individual investigators. David Angeler, Rolf Karez, and Janne Soininen as well as the Plankton Ecology Lab and members of the Nutrient Network provided helpful insights on an earlier draft of the manuscript.
Ministry of Science and Culture, State of Lower Saxony, Grants: BEFmate & MarBAS; German Research Foundation, Grant/Award Number: DFG FZT 118; Iowa Department of Natural Resources; Nutrient Network, Grant/ Award Number: DEB-0741952
© 2017 The Authors. Journal of Applied Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society.
- biodiversity change
- biodiversity loss
- human impact
- species composition
- species turnover
- time series