FLUCTUATIONS OF RODENT POPULATIONS IN RESPONSE TO RAINFALL AND FIRE IN A CENTRAL AUSTRALIAN HUMMOCK GRASSLAND DOMINATED BY PLECTRACHNE SCHINZII

Fluctuations in the composition and abundance of a small-mammal assemb lage were studied in a hummock grassland dominated by Plectrachne schi nzii at Watarrka National Park from 1988 to 1993. During this period a n experiment was conducted to examine the short-term effects of fire o n the rodents. We caught three species of rodent (Pseudomys hermansbur gensis, Notomys alexis and Mus domesticus). All species reached their greatest density in spring 1989 during an exceptionally wet period tha t extended from mid-1988 to 1990. P. hermannsburgensis was the most ab undant species and showed a 10-fold fluctuation in numbers over the sa mple period; N. alexis was the next most abundant species and showed a 5-fold increase but the population took longer to decline. M. domesti cus was recorded only during the period of high rainfall. The number o f M. domesticus was significantly less on the burnt plots than on the unburnt plots. Neither P. hermannsbursensis nor N. alexis showed signi ficant differences between burnt and unburnt plots. This study illustr ates the impact of rainfall events on the composition and density of s mall-mammal populations in spinifex grasslands in central Australia. O ur results lead to the prediction that rodent populations will achieve densities in the order of 10 individuals ha(-1) or more in regions th at experience three consecutive 6-month periods each with rainfall at 150% of the long-term average. This sequence apparently needs to follo w a dry period where rainfall is no more than 85% of the long-term ann ual average for two consecutive 12-month periods.