After recent mouse plagues in Australia the state and federal governments allowed widespread use of second-generation rodenticides. However, everything we know about farm pest management tells us this solution isn’t remotely the right thing to do. For anyone who understands ecosystemsHow ecosystems function An ecosystem is a community of lifeforms that interact in such an optimal way that how ecosystems function best, is when all components (including humans and other animals) can persist and live alongside each other for the longest time possible. Ecosystems are fuelled by the energy created by plants (primary producers) that convert the Sun's heat energy More and nature, that’s pretty much common sense already. In this blog piece I want to talk about how nurturing predators makes more food. And it doesn’t take more than a moment online to find studies that support this. But it’s so often the case that we have to wait for an overwhelming scientific discourse to prove the bleedingly obvious. Hopefully over the coming years common sense will start to prevail. But before that, we have our work cut out, trying to ensure we don’t cut ourselves off at the knees.
What prompted me to write this piece was a great article in The Conversation on the importance of snakes in farmland by Rick Shine (thank you Pennie Scott, for sharing). It makes the point that snakes ‘can collectively remove thousands of mice per square kilometre of farmland each year, which substantially increases farm productivityThe power of an ecosystem to process energy. The most productive ecosystems have reached a steady stable-state with maximum entropy production. That’s to say, the number of species has reached an optimum and the functions they fulfil, have translated free surplus energy into nutrients that is either stored inside plants and animals, or is entrained within the biological cycles that More.’
Predator-prey optimisation in farmland habitats
After reading the aforemetioned study my thoughts were that the frequency of mouse plagues would also be kept under control by maintaining numbers low across the whole ecosystem and that “I imagine that reducing snake numbers even around grain sheds could create a nice ‘super-spreader’ event.” Snakes certainly eat a lot of mice, as the author points out:
If each adult brown snake consumes around 100 wild mice each year – which is likely an underestimate – together this must equate to about 10,000 mice per square kilometre.
Rick Shine, The Conversation
Mice are also what’s known as an r-selected species: They can breed very fast. Most predators are k-selected: long-lived and slow to breed. If conditions are right, a small surplus of a fast-breeding species can create runaway reproduction cycles. It’s like the way COVID spread when it got a bit colder and everyone stayed indoors. The threshold for an outbreak is a slight imbalance of background conditions.
Snakes, like mice and birds of prey, have all become common enemies of the modern-day farming system. But mostly, the vendetta imposed on all wild animals in our farmland areas is counter-effective and unnecessary.
Simple rules to keep mouse plagues under control
Sure enough, a quick Google search and I found evidence for exactly what I guessed. A paper published in 2010 titled ‘Spatial variability in ecosystem services: simple rules for predator-mediated pest suppression.’
‘Simple’, apparently. Well, simple enough if you can convince anyone to take enough time and care, to rebuild the supporting farmland ecosystem. But allow me to summarise. The scientists built a modelThe process, either mathematically or in the human brain, of creating an internal version of something that we can refer to, to better understand how it functions and our place within. Scientific modelling is where we take the best knowledge we have and build a version of what will happen, if we assume certain parameters. For example, we might model More and created 1,000 simulated landscapes. They had two types of predators:
- Poor dispersal (e.g. snakes or other animals with limited mobility); and
- Good dispersal (e.g. birds of prey, that can fly longer distances).
They then varied the distance between patches of predators and patches of prey.
Unsurprisingly they found that:
- Landscapes with an average shorter distance between predator and prey patches, had overall lower pest density.
- They also found that the more mobile predators provided the best pest-suppression in the majority of landscapes, except for one exception.
- For poorly-dispersing predators, patches needed to be especially closer together.
This is simple common sense. In the case of snakes, you want those around your grain sheds, where the mice occur at especially high density. Farmers that kill even a few snakes are compromising their livelihoods. At a larger scale, you need widespread patches of predators to suppress pests across the landscape.
The authors conclude that:
‘the spatial arrangement of source habitatsWhat is habitat for animals and people? Habitat, hence the word "habitable" describes the natural surroundings in which any animal (or human) lives, that houses basic needs, such as food and shelter. Vegetation, for example, is habitat for animals. On its own, habitat is not necessarily stable or sustainable, which is why it differs from an ecosystem. Habitat in disrepair More for natural enemies of agricultural pest species can have profound effects on their potential to colonize crops and suppress pest populations.’
Bianchi et al, 2010
Band aid solutions or cut off at the knees?
Someone asked me the other day if the action of attacking a ‘pest’ species was like a band-aid solution. No, I said, what we are doing is something akin to me saying ‘ah, the tip of my finger hurts’ and cutting that off, then ‘ooh, my finger hurts’ and cutting that off. Then ‘aagh my hand hurts’ and cutting that off … all the way to the knees. You get the picture.
We really do need band aid solutions though! That’s to say, a very carefully used, temporary measure designed to keep problems at bay, while buying nature time to restore itself. This is about being ‘nature-positive‘, in other words, protecting the underlying system that maintains the life support we depend on.
Rebuilding interactive ecosystem resilience
Many studies about wildlife interactions fall short of drawing enough of a connection between predators, landscapes and ecosystem life support services. That’s fine. Academic studies have to be highly targeted. But there are few ecologists equipped with a deep enough knowledge of ecosystem interactions to understand how these are likely to play out.
The following “ecology quote of the day” was raised by Anthony Ricciardi on Twitter:
“We often talk about conservationWhy is animal conservation important? Animal conservation is important, because animals are the only mechanism to create biodiversity, which is the mechanism that creates a habitable planet for humans. Without animals, the energy from today’s plants (algae, trees, flowers etc) will eventually reach the atmosphere and ocean, much of it as carbon. The quantity of this plant-based waste is so More in the context of species. But it’s the interactions which are the glue that holds the entire system together”
Professor Todd Palmer, Lions make fewer zebra kills due to ‘chain reaction’ of invasive ants, study finds (The Guardian)
Palmer was talking about a study just published, which shows how the introduction of a single invasive ant species has caused lions to catch fewer zebras. It does make me wonder whether that would have had such catastrophic outcomes if the ecosystem had not already been compromised by far fewer large animals, including lions. When the structure of ecosystems is simplified, it increases the risk of extreme fluctuations or change. Rebuilding wildlife populations reduces the opportuity for species to overwhelm the system.
Flagrant over-use of pesticides
Mouse plagues can never be stopped completely, even by using chemicals. But it is a fact that their frequency of occurrence and intensity is massively reduced by predators like snakes and birds of prey … particularly owls, kestrels and so forth.
‘Like baiting, predators are unlikely to stop plagues from occurring, but enhancing the density of predators should
Johnstone & Menz – An independent review of the evidence under-pinning the Rewilding of Southern Yorke Peninsula
limit the magnitude of plagues at considerably less cost compared to pesticides.’
As I described in the article below, second-generation rodenticides are now so toxic, that consumption of one poisoned mouse is enough to kill any bird outright. It defies belief that we can sell these poisons in supermarkets and indiscriminately spread them over our farming country.
‘The NSW government had secured a supply of 10,000 litres of bromadiolone and Marshall said in May it would be “the equivalent of napalming mice across rural NSW.”
The Guardian, June 2021
Our flagrant misuse of pesticides is about to create another ‘silent spring’ by wiping out every bird of prey across whole landscapes essential for our livelihoods and food. This will have catastrophic consequences for our farmers and take decades to undo.
Conclusion
The solutio is simple. Stop the widespread engineered killing of animals where it’s clearly stupid and pointless.
We’re grossly overcompensating using chemical warfare. Nature ‘prunes’ populations like a bonsai master. But this something we can’t do ourselves. It’s not practical. We neither have the tools or resources to act with such precision.
We need other animals to do this for us. Moreover, we don’t need huge numbers of them. Even small populations of predators in the right places can have huge benefits. Farmers should be coveting the occurrence of wildlife on their land, not despising it.
This is something we will need to relearn … and fast … if we’re to have the best chance of survival.
