Which dung attracts Australian savanna dung beetles, and how do they respond to different fire regimes?

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Dung beetles are ecologically important insects worldwide, but the ecology of Australia's dung beetles is poorly known. This first ecological study of dung beetles in an Australian tropical savanna documented species composition, food preferences and responses to fire.

Researchers used dung from five types of vertebrates, as well as mushrooms, as bait. They sampled nine plots at the Territory Wildlife Park near Darwin under experimental fire regimes maintained over 15 years: three replicate plots each for high fire severity, moderate fire severity and unburnt conditions.

The samples consisted entirely of nine native species in the genus Onthophagus. Dog dung was the most attractive bait, recording all nine species and nearly 80% of all individuals. No beetles were recorded at either wallaby dung or magpie-goose dung.

Dung beetle abundance was highest under high fire severity and was negatively correlated with woody vegetation cover. This pattern was driven by the two most common species, O. minsiculus and O. nr. quadripunctulatus.

The results indicate that Onthophagus is the dominant genus in dung beetle assemblages of monsoonal Australia, as it is in open habitats of the Australian wet tropics. All Onthophagus species sampled were relatively small, with body lengths ≤10 mm, and were ‘tunnellers’: they store dung and other food resources in tunnels dug immediately below the food source.

Such overwhelming dominance by small tunnellers does not occur in African savannas. The study attributes this contrast to the far lower availability of large mammalian dung in Australia.