Competition between Two Australian Rodent Species: A Regression Analysis

Abstract

Empirical evidence and observations suggest that competition exists between two native rodents, Rattus lutreolus velutinus and Pseudomys higginsi , living in a wet sclerophyll forest, Tasmania, Australia. We used a standardized regression technique to assess competition between the two species and its temporal changes throughout the year. With our time-series data, we also tested the validity of our estimated competition coefficients by comparing regression residuals for a given species in one season to that in another. Overall, the two species competed asymmetrically for space with R. l. velutinus competitively dominant over P. higginsi . In winter (June-October), competition was low, and it reached a maximum during the breeding season (November-April). In the dispersal period (March-May), intensity of competition decreased, but was still higher than in winter, as subadults entered the trappable population. Estimated competition coefficients are validated by analyzing residuals from those three seasons. Results indicate that competitive ability in ground-dwelling small mammals is correlated positively with habitat specialization, but both may be related to body size. Intensity of competition also depends on the population phase of competing species. Our findings suggest that the standardized regression technique can be used reliably to uncover community patterns.