The utility of covariances: a response to Ranta et al

Abstract

In an earlier publication (Houlahan et al. 2007) we reviewed trends in population covariances within communities across a range of long-term empirical data sets. We used these results to argue that compensatory dynamics are rare in natural communities. Ranta et al. (2008) explored interspecific interactions in a simulated environment and showed that 'negative community covariance can be absent even in strongly competitive communities and can be found present in communities without competitive interactions'. On this basis they conclude that 'the negative community covariance method . .. is of limited practical value when attempting to detect the presence of interspecific interactions among species in a community, or the relative importance of competition and environment in driving population fluctuations.' There are three closely related points to consider here: first, exactly what is shown by demonstrating an absence of negative community covariance in some strongly competitive communities; second, what is shown by demonstrating negative community covariance in the absence of competition; and third, what these results say about the general utility of the community covariance method.

Citation

Houlahan, J.E.; Cottenie, K.; Cumming, G.S.; Currie, D.J.; Findlay, C.S.; Gaedke, U.; Legendre, P.; Magnuson, J.J.; McArdle, B.H.; Stevens, R.D.; Woiwod, I.P.; Wondzell, S.M. 2008. The utility of covariances: a response to Ranta et al. Oikos. 117: 1912-1913.