Ecological tannin assays: a critique.

The concept of protein precipitation potential has recently been introduced by Wisdom et al. (1987) as a means to combine chemical and protein precipitation assays of tannins for ecological studies. The definition of protein precipitation potential was not theoretically rigorous, and data analysis was obscure. Our attempts to repeat the tannin extraction procedure gave incomplete recovery (24% loss of quebracho) of condensed tannins, the only type considered by Wisdom et al. In contrast we found their method efficient for hydrolysable tannins (80% recovery of tannic acid) which were undetected by their chemical assay of tannins. Their protein precipitation assay was confounded by chemical interference from both types of tannins. We conclude with recommendations for this type of analysis.