The Outback is not the first place you expect some great research, but the discovery that dingoes affect the whole ecosystem of Australia’s back yard is educational for many and instructive for all. The cycling of nutrients is always studied with respect to the bottom end of the food chain. Here the
influence on the intensity and spatial organisation of herbivory (that’s kangaroos) proves just how useful top predators such as the dingo are in reality.
Basic services are provided to ecosystems by producers and myriad action by the microflora and microfauna. They cycle all the important materials and store carbon but the vegetation is heavily influenced by the abundance of consumers. A trophic cascade exists when predators limit herbivores’ plant consumption. This of course can simply be through fear of predation (non-lethal), or by lethal hunting.
Criticism of trophic cascade theory lies in the lack of experimental evidence and possibilities of other factors influencing the herbivory, but the great dingo fence provides superb experimental possibilities. Built between 1900 and 1960 to reduce sheep losses in SE Australia, it stretches for an amazing 5600km (that’s 3,480 miles, Mr Trump- just as a guide!) Shooting and poisoning (with sodium fluoroacetate) are well-recognised as contributory factors to the reduction in dingo populations that continues to this day.
Despite this, the wild dog species, mixed with many domestic hybrids, is quite common in the NW of Queensland and South Australia. The study areas took full advantage of the rarity of dingoes SE of the fence and these common dingoes in the Strzelecki Desert area. Sand dunes and clay areas receive <250mm of rain annually while the vegetation is characteristically of the Sand Plain Mulga Shrubland community (Acacia spp, and Dodonia viscosa, with grasses and
forbs forming an understorey.
The abundance of 2 kangaroo species was assessed by night spotlighting at 15km/hr over 30km of dirt tracks, from the back of vehicles. Low frequencies were found where dingoes were present, so distance sampling methods were not used. Dingo scats assessed their numbers, on 5km walks on the same dirt tracks, but they also provided invaluable evidence of diet. No livestock were present in the conservation areas used and physical variables were assessed by using identical herbivore exclusion experiments on each side of the great fence. Kangaroo damage when hurdling the 2m exclusion zone fences must have caused some hilarity but curtailed some of the experimentation!
Results appeal directly to those who insist this wild dog species should retain its place in Australia’s ecosystems. When rare, kangaroos and rodents form much of the diet, but when common, the dingo diet contains only 1% kangaroo. Mammals such as rabbits formed the predominant prey in these areas, beyond the fence. The critical finding in many ways was the negative effect of excluding kangaroos on total carbon nitrogen and available phosphorus when dingoes were also rare. When dingoes were common, not only did the kangaroos reduce in numbers, the C, N and available phosphorus figures were much higher. The
top-down effect was obvious, right down to this soil nutrient pool.
Vegetation cover in this desert region, despite rainfall variations, remained much higher when kangaroos are excluded or restrained by dingo predation. Lack of litter build up and loss of nutrients to low lying areas is predictable in areas where kangaroos are numerous. What is likely is that dingoes can mightily influence soil nutrient pools in unexpected ways, creating higher primary productivity across the whole continent where they roam free. Other predators on all continents and in the oceans could be having exactly the same effects, unknown to us or any science research, but hinted at by many observations.
Good luck with persuading Australia to finally accept that the sheep-killer is actually a benefit to the community, the ecosystem and the whole nation! Timothy Morris and Mike Letnic of the University of New South Wales in Sydney wrote their paper today in the Proc Roy. Soc. B asRemoval of an apex predator initiates a trophic cascade that extends from herbivores to vegetation and the soil nutrient pool. We had a story previously that brought in cat control as yet another benefit of having dingoes around! Read all about it in
The strange case of cats and dingo dogs. Next, we’ll have a look at those New Guinea singing dogs---.