Echidnas are not just cute holdovers from a time when mammals laid eggs, and that also just happen to possess some of the world's strangest genitals. According to a new study, they're also essential to the fertility of Australia's depleted soils. The feat makes them a “keystone species”, one on which the entire ecosystem depends.
A team led by Dr Christofer Clemente of the University of the Sunshine Coast, Queensland, was intrigued by the way echidnas walk, combining aspects of mammalian locomotion with features associated with reptiles. Clemente attached GPS monitors and accelerometer loggers to 11 short-beaked echidnas (Tachyglossus aculeatus) and let them roam.
The findings showed the critter's adorable rolling waddle, a consequence of short arms suited to digging but less appropriate for running. It also found that on those strong, stubby arms may rest a lot of the biological capacity of their homeland.
“Echidnas spent, on average, 12 percent of their time digging, which indicates their potential to excavate up to 204 meters cubed (7,200 cubic feet) of soil a year,” the team report in the Journal of Experimental Biology, based on the echidnas' measured capacity to displace their body weight in the space of a minute. The species remain sufficiently common that this adds up.
“If you have 12 echidnas, they are moving the volume of an Olympic-sized swimming pool of dirt a year, which is quite a lot,” Clemente said in a statement.
Their walk may be exceptionally ancient, but their digging skills are awesome. Taronga Zoo
From the echidna's perspective, the digging is conducted in search of the termites and ants they feed upon, and to create burrows to live in. In the process, the excavation mixes up soil and has been shown to almost double the amount of water the soil can absorb and the organic material it can retain, which in turn leads to much greater diversity of inhabiting species. Echidnas are not the continent's only diggers, but their spines have protected them against introduced predators while other burrowing species have declined or become extinct.
The research also reveals a wealth of information about what else echidnas do with their time (not much – they're usually resting when not digging), how fast they move, and the length of their gait. Despite their slow speed and fondness for snoozing, echidnas manage to travel greater distances every day than most similar-sized mammals. In hot weather, they run faster but for much shorter times, apparently keen to get back to the cool of the undersoil.
Most intriguingly, their movements fall somewhere between the upright walk of most four-legged mammals and the sprawling motion of lizards. Echidnas are thought to have evolved from aquatic creatures similar to the platypus, so it is curious their walk may resemble very ancient ancestors as they took the first steps towards becoming mammals.