Posted by Jamie Stavert @jamiestavert
It seems ironic that dung beetles, a group of insects best known for their fondness of other animal’s excrement, can attribute their proliferation to the diversification of flowers. A recent study by Nicole Gunter and colleagues shows that the explosion of dung beetle diversity in the Cretaceous was due to a change in dinosaur diet to the newly evolved flowering plants. This low fibre, high nutrient dinosaur diet produced dung that dung beetles found more palatable and probably more appealing than bland, chewy conifer-containing crap.
Burrowed deeply within this fascinating story are New Zealand’s 15 curious and enigmatic dung beetle species, which probably evolved for 80mya in post-Gondwana isolation. It is unsurprising therefore, like many of NZ’s biological oddities, that NZ’s dung beetles are globally unique. Native NZ dung beetles are small, flightless, forest dwelling and, unlike their distant continental relatives, enjoy munching on bird poo (although, as we discovered, they’ll eat almost anything). Interestingly, birds are basically shrunken dinosaurs, so bird poo probably isn’t that different from what dinosaur poo would’ve been like. Following the extinction of dinosaurs, further diversification of dung beetles was elicited by the radiation of mammals (almost everywhere but NZ). But because they did not have the smorgasbord of poo that was available to dung beetles elsewhere in the world, the NZ taxa are relatively species poor.
And there’s another twist to the story: despite the extinction of most native birds from the NZ mainland, native dung beetles are often recorded in massive numbers. This begs the question: without native bird dung, what are these dung beetles eating and what is their ecological role?
We found that NZ dung beetles feed on a range of native reptile, bat, bird and insect dung and dead animals (basically everything that was put in front of them). We also showed that NZ dung beetles enjoy calamari, happily consuming the rotten squid that we fed them. Accordingly we suggested that NZ dung beetles evolved a broad generalist diet due to the lack of mammal poo. We also proposed that NZ dung beetles would have utilised marine resources such as seabird poo, carcasses and vomit. Before human arrival, NZ forests were a seething mass of seabirds, and native dung beetles could have been a key link in the flow of nutrients from the marine environment to forest ecosystems.
But what about today where many of NZ’s native birds have become extinct or are confined to offshore islands? Perhaps dung beetles are one of the few benefactors of mammal introductions to NZ? We found that NZ dung beetles are also fond of mammal stools, particularly dog poo. Indeed nothing beats a rich, meaty Labrador turd… one certainly ponders the direction one’s life is taking while head-deep in a council dog shit bin…
Jamie Stavert is a PhD candidate at the Centre for Biodiversity & Biosecurity, School of Biological Sciences, University of Auckland. His MSc research was on dung beetles, but he has switched to smelling flowers and is now investigating how functional traits influence ecosystem function and species’ responses to environmental change in pollination systems. He is supervised by Jacqueline Beggs, Anne Gaskett, David Pattemore and Nacho Bartomeus.