R.L. Nudds and S.A. Oswald argued in 2007 that there is poor empirical support for Allen's rule even if it is an "established ecological tenet".[4] They said that the support for Allen's rule mainly draws from studies of single species, since studies of multiple species are "confounded" by the scaling effects of "Bergmann's rule" and alternative adaptations that counter the predictions of Allen's rule.[4]