THE RELATIONSHIP AMONG DIET, ALIMENTARY-TRACT MORPHOLOGY, AND LIFE-HISTORY FOR 5 SPECIES OF RODENTS FROM THE CENTRAL ARGENTINE PAMPA

A suite of characters describing digestive tract structure has been hy pothesized to reflect the relative degree of specialization of the dig estive system of rodent species along a continuum from a proteinaceous diet of seeds and insects to a cellulosic diet of vegetation. Similar ly, it has been proposed that life history traits might reflect diet a nd digestive tract structure, with the most opportunistic species cons uming the most energy-rich diets of seeds and insects. The five member s of the rodent assemblage of agroecosystems of the Argentine pampa we re found to be omnivores and varied in the relative proportions of see ds, insects, and vegetation consumed. On a gross level, diet reflected life history; the most opportunistic species (smallest body size, hig hest fecundity, preference for disturbed habitats) consumed the most e nergy-rich diet, while the least opportunistic species consumed the mo st vegetation. However, comparative digestive tract structure was gene rally converse to that predicted, based on diet. Failure to observe pr edicted correlations may be due in part to seasonal variability in die t, lack of evolutionary relevance of crop habitats, or flaws in the un derlying hypotheses. Alternatively, the observed variation in digestiv e tract structure may reflect the spectrum of Variation encountered wi thin an omnivore rodent guild rather than the degree of food specializ ation.