Demographic and dietary responses of small mammals to high severity fire

Populations of many animal species decline after fire, with some individuals killed during the fire and others succumbing to impoverished conditions in the post-fire environment. For individuals that survive a fire, an ability to exploit scarce resources in the burnt landscape is particularly important. In this study, we compared the numbers, survival and diets of three species of small mammal at two sites in tall open-forest in the Australian Capital Territory, Australia. The first site was subjected to a high severity experimental fire in February 1980, while the second nearby site was unburnt and served as a control. Relative numbers and survival of the Agile Antechinus (Antechinus agilis) and Mainland Dusky Antechinus (A. mimetes) declined post-fire and remained lower than in the control site until spring 1980 when populations at both sites crashed following the post-mating death of males. These patterns reversed for A. mimetes in 1981 and 1982 and for A. agilis in 1982, with numbers and survival then being higher in the burnt than in the control site. Relative numbers of the Bush Rat (Rattus fuscipes) increased in a similar manner in both sites until the end of the study after 29 months, and monthly survival remained high throughout. The diets of the three species were similar between the control and burnt site before the fire. In the four months post-fire the diets of the two Antechinus species in the burnt site contained fewer ground-dwelling invertebrates compared with the control, whereas the dietary diversity of R. fuscipes in the burnt site increased due to increased consumption of food groups such as grasses and ferns that otherwise were seldom eaten. The dietary diversity of all species was similar between the two sites 12–16 months post-fire. The results suggest that the fire had short-term effects on the two species of Antechinus, most likely by depleting populations of their prey, while the demography of R. fuscipes was scarcely affected by fire owing to its ability to switch food groups within its already omnivorous diet. Dietary flexibility may be an important but often overlooked mechanism facilitating species’ persistence in post-fire environments.