COMPETITION BETWEEN 2 AUSTRALIAN RODENT SPECIES - A REGRESSION-ANALYSIS

Empirical evidence and observations suggest that competition exists be tween two native rodents, Rattus lutreolus velutinus and Pseudomys hig ginsi, 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 ti me-series data, we also tested the validity of our estimated competiti on coefficients by comparing regression residuals for a given species in one season to that in another. Overall, the two species competed as ymmetrically for space with R. l. velutinus competitively dominant ove r P. higginsi. in winter (June-October), competition was low, and it r eached a maximum during the breeding season (November-April). in the d ispersal period (March-May), intensity of competition decreased, but w as still higher than in winter as subadults entered the trappable popu lation. 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. Intensi ty of competition also depends on the population phase of competing sp ecies. Our findings suggest that the standardized regression technique can be used reliably to uncover community patterns.