Dingoes seem to be pretty controversial animals, and I think I even found about as close as you’ll get to a fight in the scientific community over the ecological roles of the dingo (what was fascinating about the exchange was not just what was said, but how it was said- scientists can be mean). A lot of the debate centers around whether dingoes are good for biodiversity and, especially, the preservation of threatened native species, or if they are disrupting ecological processes (I am sure that I haven’t even read half of the literature out there). And this discussion extends beyond dingoes to other wild dogs around the world.
Dingo (Canis lupus dingo)
What does the dingo data say? Dingoes have a diverse diet, as I mentioned before- one study found at least 29 native and 4 introduced prey species in dingo scat (Vernes et al. 2001); at least three species that dingoes prey on are threatened (Allen & Leung 2012). However, Pavey et al. (2008) found that dingoes put less pressure on rodent populations than red foxes and house cats, data echoed by Cupples et al. (2011) who found that red foxes preyed upon small mammals more than would be expected based upon their availability, while dingoes did not. Additionally, it appears that dingoes may help keep red fox numbers down- Johnson & VanDerWal (2009) found that foxes were rare where dingoes were prevalent, and Lu (2011)’s study only detected foxes in areas where dingo control was practiced. A similar situation was noted with feral cats in northern Australia (Kennedy et al. 2011). How does that impact biodiversity? To a large degree, the declines seen in Australia’s medium and small mammals since European colonization have been driven by introduced red foxes and house cats (Pavey et al. 2008; Johnson & VanDerWal 2009)- if the presence of dingoes can reduce fox and cat numbers, that should be good for Australia’s remaining small and medium-sized mammals. Ritchie & Johnson (2009)’s review of predation studies in Australia indicated that native species whose populations overlapped with the current dingo range have survived better, and that certain species, such as the dusky hopping mouse, were only found where dingoes are abundant. They also referred to the loss of a rufous hare-wallaby population partly in response to control- when the local dingoes were eradicated by poison, foxes soon moved in and predated the hare-wallabies to extinction. This type of relationship may extend to small carnivores as well- there are concerns that the removal of dingoes from areas with tiger quolls could expose the latter to unsustainable pressure from foxes (Andrew 2005).
A new way of looking at dingoes. I’m not trying to suggest that dingoes do only good in the environment: they also eat threatened species, as well as damaging the livelihoods of sheep and cattle ranchers- in the Northern Territory alone, it’s estimated that dingoes cause $2 million+ in damages to the cattle industry each year (Parks and Wildlife Service of the Northern Territory 2011). But it seems that trying to control their populations through baiting and trapping doesn’t always have the intended consequences- yes, dingoes are killed, but that doesn’t necessarily translate into safer livestock and recovery for threatened species. I found an interesting PhD thesis that looked at how the dingo population responds to baiting and trapping, and then how those responses impact other species, and the paper got me thinking about dingoes in a different way. Wallach (2011) compared sites with control programs, without control programs, and where control programs had recently ended, looking partially at numbers but also at population structure. According to the paper, that second element is the most important in determining how dingoes interact with their environment. Why? Similar to wolves, in a dingo pack only certain members reproduce; however, when pack stability is disrupted through baiting and trapping, dingoes often respond by breaking into smaller groups and becoming more productive- yes, those extra dingoes continue to be killed, but, before they are removed from the system, their behavior changes in some respects. Smaller packs must look for easier-to-subdue prey, which does make livestock more appealing, and Wallach felt that higher livestock attack rates were a result of pack disintegration. Poisoning also tends to remove animals indiscriminately, so older individuals who have perhaps learned to stay away from humans are targeted just as much as younger animals without that knowledge. There is also the possibility that hybridization is a consequence of predator control- normally a dingo pack would not allow in a domestic dog, but, when population stability is lost, single individuals may mate with dogs. Finally, without stable packs which can limit smaller predators, such as foxes, and prey on larger herbivores, such as kangaroos, you can get growing populations of those animals who then overuse available resources. Why is this information important? Something that Wallach said suggested that we may need to alter how we assess dingo roles: “It is the pack that is the top predator, not the individual dingo (78).” So, if we want to really understand how dingoes impact their environment and have the potential for supporting biodiversity, we have to look at the pack as an organism, and we have to consider the idea that killing dingoes is not a solution to conservation problems. Wallach advocated restoring ecosystems through a combination of vegetation enrichment, supporting animals that are ecosystem engineers, such as those that dig burrows used by other species, and letting apex predators regulate the system from the top.
What does this mean for other wild dogs? Well, it really depends upon the species, but there are some ideas that extend to all of them. Certainly the idea of the pack as a predator is important. Pack-living allows African wild dogs to hunt large prey cooperatively (Woodroffe et al. 2007), and larger packs increase survival for pups over 9 months of age (Buettner et al. 2007). Dholes in Asia require large packs to support the large litters which result from their entirely meat-based diet (Kamler et al. 2012). What about small carnivore regulation? In general, studies have found data that supports the idea that large carnivores limit the numbers of smaller ones (Ritchie & Johnson 2009)- and typically an increase of apex predators by a certain number will have an even larger negative impact on the number of smaller predators. Wolves, for example, limit coyote numbers- wolves were eradicated from New Hampshire where I live, and coyotes are a recent addition to the fauna in NH. As I mentioned in posts regarding bobcats, coyotes can keep house cat populations down. So, I think that looking at predator and ecosystem conservation involves looking at predator social structure and which other predators might step into any void that is created.
Once again, this is a lot of information to process- dingoes seem to have important roles in Australian ecosystems, but teasing apart the different aspects is challenging, especially when threatened species and people’s livelihoods are involved. The same is true for other wild dogs around the world- think of the controversy about wolf reintroduction in Yellowstone or the worries about coyotes in urban areas. Living with wild dogs is a challenge, as is finding ways to look at predator ecology from a dispassionate viewpoint that includes all aspects. I have no illusions about my ability to do the latter, but I’m hopeful that more complete understanding of how dingoes and other wild dogs fit into environments will make me better able to assess where I fit in- if you are in the same position, I hope to suggest some options in my next post when I focus a bit more on the human element.
Works cited:
Allen, BL & LK-P Leung. 2012. Assessing predation risk to threatened fauna from their prevalence in predator scats: dingoes and rodents in arid Australia. PLoS ONE 7 (5): e36426.
Andrew, DL. 2005. Ecology of the tiger quoll Dasyurus maculatus maculatus in coastal New South Wales. MSc thesis, School of Biological Sciences, University of Wollongong.
Buettner, UK, Davies-Mostert, HT, du Toit, JT & MGL Mills. 2007. Factors affecting juvenile survival in African wild dogs (Lycaon pictus) in Kruger National Park, South Africa. Journal of Zoology 272: 10-19.
Cupples, JB, Crowther, MS, Story, G & M Letnic. 2011. Dietary overlap and prey selectivity among sympatric carnivores: could dingoes suppress foxes through competition for prey? Journal of Mammalogy 92: 590-600.
Johnson, CN & J VanDerWal. 2009. Evidence that dingoes limit abundance of a mesopredator in eastern Australian forests. Journal of Applied Ecology 46: 641-646.
Kamler, JF, Johnson, A, Vongkhamheng, C & A Bousa. 2012. The diet, prey selection, and activity of dholes (Cuan alpinus) in northern Laos. Journal of Mammalogy 93: 627-633.
Kennedy, M, Phillips, BL, Legge, S, Murphy, SA & RA Faulkner. 2011. Do dingoes suppress the activity of feral cats in northern Australia? Austral Ecology 37: 134-139.
Lu, A. 2011. Presence of the dingo (Canis lupus dingo) on risk sensitive foraging of small mammals in forest ecosystems. Independent Study Project (ISP) Collection Paper 1130.
Parks and Wildlife Service of the Northern Territory. 2011. A management program for the dingo (Canis lupus dingo) in the Northern Territory. Department of Natural Resources, Environment and The Arts.
Pavey, CR, Eldridge, SR, & M Heywood. 2008. Population dynamics and prey selection of native and introduced predators during a rodent outbreak in arid Australia. Journal of Mammalogy 89: 674-683.
Ritchie, EG & CN Johnson. 2009. Predator interactions, mesopredator release and biodiversity conservation. Ecology Letters 12: 982-998.
Vernes, K, Dennis, A & J Winter. 2001. Mammalian diet and broad hunting strategy of the dingo (Canis familiaris dingo) in the wet tropical rain forests of northeastern Australia. Biotropica 33: 339-345.
Wallach, AD. 2011. Reviving ecological functioning through dingo restoration. PhD thesis, School of Earth and Environmental Sciences, University of Adelaide.
Woodroffe, R, Lindsey, PA, Romanach, SS, & SMK Ole Ranah. 2007. African wild dogs (Lycaon pictus) can subsist on small prey: implications for conservation. Journal of Mammalogy 88: 181-193.