DIETARY MIXING IN A GENERALIST HERBIVORE - TESTS OF 2 HYPOTHESES

It has been demonstrated in several taxa that generalists grow better when they ingest a mixed diet than when they are restricted to just on e or two items, but there are few cases that provide definitive eviden ce for how this benefit is achieved. Two hypotheses are addressed conc erning the possible benefits of feeding on a variety of foods: (1) mix ing foods increases the quality of the overall diet by improving the n utrient balance and (2) mixing improves the diet due to dilution of an y one plant secondary compound. The generalist grasshopper Schistocerc a americana was used in a series of experiments to distinguish between the two hypotheses. Experiments using artificial foods with complemen tary nutrients demonstrated that dietary mixing improves growth while the amount ingested is decreased. Nutritionally identical foods with d iffering plant secondary compounds led to different growth rates, but insects able to mix generally grew at intermediate rates. Experiments with domestic or wild plant mixtures gave results generally closer to the pattern found with complementary nutrients than the pattern found with differing poisons, but both hypotheses are supported to some exte nt.