Tag Archives: pest management

The Anatomy of an Ecological Controversy – Dingos and Conservation in Australia

Conservation is a most contentious discipline, partly because it is ecology plus a moral stance. As such you might compare it to discussions about religious truths in the last several centuries but it is a discussion among scientists who accept the priority of scientific evidence. In Australia for the past few years there has been much discussion of the role of the dingo in protecting biodiversity via mesopredator release of foxes and cats (Allen et al. 2013; Colman et al. 2014; Hayward and Marlow 2014; Letnic et al. 2011, and many more papers). I do not propose here to declare a winner in this controversy but I want to dissect it as an example of an ecological issue with so many dimensions it could continue for a long time.

Dingos in Australia are viewed like wolves in North America – the ultimate enemy that must be reduced or eradicated if possible. When in doubt about what to do, killing dingos or wolves has become the first commandment of wildlife management and conservation. The ecologist would like to know, given this socially determined goal, what are the ecological consequences of reduction or eradication of dingos or wolves. How do we determine that?

The experimentalist suggests doing a removal experiment (or conversely a re-introduction experiment) so we have ecosystems with and without dingos (Newsome et al. 2015). This would have to be carried out on a large scale dependent on the home range size of the dingo and for a number of years so that the benefits or the costs of the removal would be clear. Here is the first hurdle, this kind of experiment cannot be done, and only a quasi-experiment is possible by finding areas that have dingos and others that do not have any (or a reduced population) and comparing ecosystems. This decision immediately introduces 5 problems:

  1. The areas with- and without- the dingo are not comparable in many respects. Areas with dingos for example may be national parks placed in the mountains or in areas that humans cannot use for agriculture, while areas with dingo control are in fertile agricultural landscapes with farming subsidies.
  2. Even given areas with and without dingos there is the problem of validating the usual dingo reduction carried out by poison baits or shooting. This is an important methodological issue.
  3. One has to census the mesopredators, in Australia foxes and cats, with further methodological issues of how to achieve that with accuracy.
  4. In addition one has to census the smaller vertebrates presumed to be possibly affected by the mesopredator offtake.
  5. Finally one has to do this for several years, possibly 5-10 years, particularly in variable environments, and in several pairs of areas chosen to represent the range of ecosystems of interest.

All in all this is a formidable research program, and one that has been carried out in part by the researchers working on dingos. And we owe them our congratulations for their hard work. The major part of the current controversy has been how one measures population abundance of all the species involved. The larger the organism, paradoxically the more difficult and expensive the methods of estimating abundance. Indirect measures, often from predator tracks in sand plots, are forced on researchers because of a lack of funding and the landscape scale of the problem. The essence of the problem is that tracks in sand or mud measure both abundance and activity. If movements increase in the breeding season, tracks may indicate activity more than abundance. If old roads are the main sampling sites, the measurements are not a random sample of the landscape.

This monumental sampling headache can be eliminated by the bold stroke of concluding with Nimmo et al. (2015) and Stephens et al. (2015) that indirect measures of abundance are sufficient for guiding actions in conservation management. They may be, they may not be, and we fall back into the ecological dilemma that different ecosystems may give different answers. And the background question is what level of accuracy do you need in your study? We are all in a hurry now and want action for conservation. If you need to know only whether you have “few” or “many” dingos or tigers in your area, indirect methods may well serve the purpose. We are rushing now into the “Era of the Camera” in wildlife management because the cost is low and the volume of data is large. Camera ecology may be sufficient for occupancy questions, but may not be enough for demographic analysis without detailed studies.

The moral issue that emerges from this particular dingo controversy is similar to the one that bedevils wolf control in North America and Eurasia – should we remove large predators from ecosystems? The ecologist’s job is to determine the biodiversity costs and benefits of such actions. But in the end we are moral beings as well as ecologists, and for the record, not the scientific record but the moral one, I think it is poor policy to remove dingos, wolves, and all large predators from ecosystems. Society however seems to disagree.


Allen, B.L., Allen, L.R., Engeman, R.M., and Leung, L.K.P. 2013. Intraguild relationships between sympatric predators exposed to lethal control: predator manipulation experiments. Frontiers in Zoology 10(39): 1-18. doi:10.1186/1742-9994-10-39.

Colman, N.J., Gordon, C.E., Crowther, M.S., and Letnic, M. 2014. Lethal control of an apex predator has unintended cascading effects on forest mammal assemblages. Proceedings of the Royal Society of London, Series B 281(1803): 20133094. doi:DOI: 10.1098/rspb.2013.3094.

Hayward, M.W., and Marlow, N. 2014. Will dingoes really conserve wildlife and can our methods tell? Journal of Applied Ecology 51(4): 835-838. doi:10.1111/1365-2664.12250.

Letnic, M., Greenville, A., Denny, E., Dickman, C.R., Tischler, M., Gordon, C., and Koch, F. 2011. Does a top predator suppress the abundance of an invasive mesopredator at a continental scale? Global Ecology and Biogeography 20(2): 343-353. doi:10.1111/j.1466-8238.2010.00600.x.

Newsome, T.M., et al. (2015) Resolving the value of the dingo in ecological restoration. Restoration Ecology, 23 (in press). doi: 10.1111/rec.12186

Nimmo, D.G., Watson, S.J., Forsyth, D.M., and Bradshaw, C.J.A. 2015. Dingoes can help conserve wildlife and our methods can tell. Journal of Applied Ecology 52. (in press, 27 Jan. 2015). doi:10.1111/1365-2664.12369.

Stephens, P.A., Pettorelli, N., Barlow, J., Whittingham, M.J., and Cadotte, M.W. 2015. Management by proxy? The use of indices in applied ecology. Journal of Applied Ecology 52(1): 1-6. doi:10.1111/1365-2664.12383.

Why We Cannot Forget about Weeds

Weeds are one of world’s most significant ecological problems. As such it is surprising that the word “weeds” does not appear at all in Sutherland et al. (2013), and only once in Sutherland et al. (2006). (Perhaps there are no weeds in the UK.) Weeds affect plant and animal communities in national parks and nature reserves as well as in agricultural landscapes and cities. We have taken a benign neglect attitude toward weeds, perhaps because they are everywhere, but ecologists may also wish to avoid the word ‘weed’ because it is not a useful aggregate term about which we can draw some ecological generalizations. How should we respond to weeds?

I consider ‘weeds’ as a collective term for what might be the worst global example of serious ecological problems (Strayer 2012). But is this collective term a very useful one? At the first step when we deal only with plants, we get confused with native plants and exotic plants. A utilitarian perspective looks at all plants to see if they are useful or harmful for humans. So some conservation biologists want to get rid of all exotic plants outside of gardens and crops, and others wish to limit all harmful plants, whether native or exotic, and call them ‘weeds’. So the rose in your front yard is indeed an exotic species but a good one. Farmers want to get rid of at least some weeds to maximize production but at the same time to tolerate other exotic species that increase production. Weeds might be thought of as a convenient grouping to simplify ecological generalizations. But alas it has not been so.

The War against Weeds is in general not going well for conservation biologists (Downey et al. 2010). While biological control is very useful for some weeds, it does not at present seem to work for most weeds of national concern. So it does not seem to be a universal solution. Herbicides work for a time and then natural selection intervenes. The problem is that weed problems are very much a local problem in being species-specific and environment-specific, so that there is no overall weed strategy that works everywhere (Vilà et al. 2011). If one is interested in community productivity, weeds may increase plant biomass which might be considered a good result for the ecosystem. Graziers may encourage weeds that plant ecologists would consider destructive to natural communities. Ecosystem ecologists might welcome weeds that increase plant cover if they reduce soil erosion and nutrient leakage into water bodies.

This conflict of interest comes home to us in quarantine restrictions on weeds. In Australia government research scientists work to increase the tolerance of exotic pasture grassess to cold and drought, even though the species in question is a weed of national significance, and improving it genetically will make it more invasive in natural communities (Driscoll et al. 2014). The problem comes back to who wants what kind of an ecological world. Generalist grazing mammals may care little about the exact species composition of the grasslands they inhabit, or alternately they may be poisoned by specific weeds that are toxic to farm animals. The devil rests in the details, so the general message is that we cannot forget species names and attributes in the War on Weeds.

As a minimum, we ought to encourage our governments to place quarantine restrictions on all plant species listed as global weeds of significance. For the present time the best predictor of whether or not an introduced plant will become a destructive weed is: what happened to that plant in other countries to which it was introduced? That you can still buy at your local plant store the seeds of an array of weeds of national significance shouts to ecologists that quarantine systems needs to be strengthened. The War on Weeds is greatly under-financed like many long term problems in ecology, and we should put more effort into developing tactics to deal with destructive weeds rather than ignoring them.

Downey, P.O. et al. 2010. Managing alien plants for biodiversity outcomes—the need for triage. Invasive Plant Science and Management 3(1): 1-11. doi:10.1614/ipsm-09-042.1.

Driscoll, D.A. et al. 2014. New pasture plants intensify invasive species risk. Proceedings of the National Academy of Sciences USA 111(46): 16622-16627. doi:10.1073/pnas.1409347111.

Strayer, D.L. 2012. Eight questions about invasions and ecosystem functioning. Ecology Letters 15(10): 1199-1210. doi:10.1111/j.1461-0248.2012.01817.x.

Sutherland, W.J. et al. 2006. The identification of 100 ecological questions of high policy relevance in the UK. Journal of Applied Ecology 43(4): 617-627. doi:10.1111/j.1365-2664.2006.01188.x.

Sutherland, W.J. et al. 2013. Identification of 100 fundamental ecological questions. Journal of Ecology 101(1): 58-67. doi:10.1111/1365-2745.12025.

Vilà, M., et al. 2011. Ecological impacts of invasive alien plants: a meta-analysis of their effects on species, communities and ecosystems. Ecology Letters 14(7): 702-708. doi:10.1111/j.1461-0248.2011.01628.x.

On House Mouse Outbreaks in Australia

It occurred to me after some recent discussions that the problem of house mouse outbreaks in Australia is almost a paradigm for modern ecological science. A brief synopsis. At irregular intervals house mice (an introduced pest) reach high densities in the wheat growing areas of eastern and southern Australia, and cause serious damage to wheat, barley, oats, and sunflower crops. There are two approaches to this applied problem.

The ecological approach is to understand why these outbreaks occur and why for many years (2-9 years) between outbreaks, hardly a mouse can be found. This approach has been highly successful led by a series of excellent Australian ecologists over the last 40 years. The key limitation is food, combined with social interactions, and the food supply is driven by rain at critical times of the year to provide seeds for the mice. There are no competitors for house mice, and there are a few insignificant predators, overwhelmed by the mouse’s high reproductive rate. These ecological facts are clearly known, and the job now is to build the best predictive models to help the farmers anticipate when the outbreak is coming. There are still important ecological questions to be studied, to be sure, but the broad outline of the ecological play is well described.

The management approach is much simpler because farmers can control house mice with poison, primarily zinc phosphide, and for them the question is when to poison, and secondarily (over time and with more research) can we develop better poisons so there are few non-target problems. Poisoning costs time and money so good farmers wish to minimize these costs.

The long-term issues get lost in this situation, a model of the way the world operates now with ecological and environmental problems. Questions about sustainability multiply in any system dependent on poisons for a solution. Will the target organisms become resistant so the poison does not work? Many examples exist of this already. Are there any long-term problems with soil organisms, or non-target species? No research yet on these issues, and perhaps they are more serious with herbicide applications in agriculture. And while predators do not control house mice during outbreaks, they do eat many of them and this food pulse may have implications for the wider ecosystem. We focus on farming and forget the wider ecosystem which has no dollars attached to it.

Ecologists recognize that these issues are not the farmers’ fault, but we raise the question of who worries about the long-term future of this system, and the answers to these long-term questions. The government is rushing to get out of long-term ecological and agricultural research and we leave problems that do not have immediacy.

Consequently we become short-sighted as a society. Long-term research becomes 1-3 years and not the 50-100 years that ecologists would support. And consequently applied ecologists bounce from one problem to the next under the paradigm that, no matter what we do, science will come up with a technological fix. There should be a better way. To go back to our house mice, we might ask (for example) if we implement no-till agriculture, what will be the consequences for house mouse survival and future outbreaks? The practical minister of agriculture will respond that we have no time or money for such research, so we lurch along, managing the world in an ad-hoc manner. There should be a better way. But meanwhile we must follow the money.