, Volume 21, Issue 2, pp 297-299,
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Date: 18 Nov 2011

Response to “traits and stress: keys to identify community effects of low levels of toxicants in test systems” by Liess and Beketov (2011)

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To Editor,

We read with great interest the paper entitled “Traits and stress: keys to identify community effects of low levels of toxicants in test systems” by Matthias Liess and Mikhail Beketov (Liess and Beketov 2011). The paper presents a new way to analyse data from microcosms and mesocosms, which the authors claim that to be more sensitive than the commonly-used principal response curves (PRC) method (Van den Brink and Ter Braak 1999). Since PRC was developed more than a decade ago, new developments in the field of analysing community responses to stress are very welcome. However, after reading the paper, we have concluded that their new method, i.e. SPEARmesocosm, may not offer the level of improvement suggested and in this letter to the editor we will briefly explain why.

Both PRC and SPEARmesocosm display the time-dependent treatment effects of a toxicant. The fundamental difference between the PRC and SPEARmesocosm methods is that PRC is a multivariate statistical method and SPE