Threatened mammals become more predatory after small-scale prescribed fires in a high-rainfall rocky savanna

Abstract

Understanding mechanisms underlying fire regime effects on savanna fauna is difficult because of a wide range of possible trophic interactions and feedbacks. Yet, understanding mechanisms underlying fauna dynamics is crucial for conservation management of threatened species. Small savanna mammals in northern Australia are currently undergoing widespread declines and regional extinctions partly attributable to fire regimes. This study investigates mammal trophic and ecosystem responses to fire in order to identify possible mechanisms underlying these declines. Mammal trophic responses to fire were investigated by surveying mammal abundance, mammal diet, vegetation structure and non-mammal fauna dynamics in savannas six times at eight sites over a period of 3 years. Known site-specific fire history was used to test for trophic responses to post-fire interval and fire frequency. Mammal and non-mammal fauna showed only minor responses of post-fire interval and no effect of fire frequency. Lack of fauna responses differed from large post-fire vegetation responses. Dietary analysis showed that two mammal species, Dasyurus hallucatus and Isoodon auratus, increased their intake of large prey groups in recently burnt, compared to longer unburnt vegetation. This suggests a fire-related change in trophic interactions among predators and their prey, after removal of ground-layer veg- etation. No evidence was found for other changes in food resource uptake by mammals after fire. These data provide support for a fire-related top-down ecosystem response among savanna mammals, rather than a bottom-up resource limitation response. Future studies need to investigate fire responses among other predators, including introduced cats and dingoes, to determine their roles in fire-related mammal declines in savannas of northern Australia.