Population cycles ofRattus exulans: Population changes, diet, and food availability

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Abstract
This study investigated a suggested link between population dynamics and food, especially grass seed. Rattus exulans on Tiritiri Matangi Island undergo large annual fluctuations in density. Breeding occurred over a 3 month period and all animals that bred died in the subsequent autumn or winter. Grass seeds were the major item in the diet during most of the breeding season and the subsequent population peak. Estimates of seed abundance showed that rats took seed as soon as it was available and the population declined once grass seedfall was insufficient to support the total rodent biomass. Rats in the laboratory showed preference for some seeds but gained weight only on a mixed diet Herbage was an important food when it had its highest energy value prior to breeding. Invertebrates were available all year but were taken only when more preferred foods were unavailable. Results partially support the importance of grass seed as a determinant of breeding and population decline.