Foraging Behavior of a Vertebrate Omnivore (Rattus Rattus): Meal Structure, Sampling, and Diet Breadth
1982
Clark, Deborah A.
Diet selection by the oimnivorous black rat (Rattus rattus) was examined by detailed analysis of stomach contents of individuals from seven wild populations in the Galapagos Islands. High within—meal diversity of foods was found: nearly all stomachs contained at least four foods, and many contained eight or more. Although 77% of the rats had eaten at least one potentially filling food,no individual (N = 173) had only one food in its stomach. Meals tended to be dominated by one food; these dominant foods included a variety of plant and animal materials, but were rarely leaves. Nearly all stomachs contained at least one food present in a trace amount (<1% of contents) (°x = 2.72 trace items per stomach; N =165). The prevalence of traces from large food items (leaves, stems, and most fruits) suggests a strong sampling component in the rats' foraging behavior. A high degree of stereotype in foraging was found. Many foods were eaten by nearly all individuals. In several cases the same combination of 2—4 foods was selected by 82—100% of the rats in a population sample. Two measures of diet breadth (the number of plant species in the diet and the cumulative number of food items eaten by members of a population) and the within—meal diversity of trace items were all significantly negatively correlated with rat population density. Two food abundance indices were significantly positively correlated with rat density. These results are used to evaluate current theoretical models of nonspecialist foraging behavior.
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