Biplot presentation of diet composition data: an alternative for fish stomach contents analysis

A multivariate analysis derived from principal components analysis (PCA), a nd which allows the investigation on diet composition data, is introduced. To illustrate the method, prey composition data of stomach contents of brow n trout Saline trutta L. collected in a regulated stream were used. The die t composition, foraging strategies and related patterns of fish diet variat ion were analysed at a macrohabitat scale (i.e. riffles and glides) by way of biplots. These graphical presentations were consistent with PCA on propo rtions. (C) 2000 The Fisheries Society of the British Isles.