Alpine ants react to a changing planet with violence
The Anthropocene’s impact includes a mix of profound and more subtle changes in ecosystems. Falling in the latter camp is how it effects animal behaviour.
Research has pointed to the idea that a range of different animals behave more aggressively under warmer conditions — including humans — but little work had been done on ants.
Whatever they’re up to, it’s potentially a game-changer, given these are insects that assert their behavioural traits in massive groups and have a propensity for stinging, biting and generally throwing their weight around in various habitats.
Unrest in the mountains
Enter scientists in Austria, who set out to explore whether the behaviour of the ant Tetramorium alpestre, which lives at high elevations in the Alps, was affected by genetic, social and environmental differences.
They sampled ants from a range of altitudes, putting them and their environment through a range of analyses.
Two key connections stood out from the wealth of data: worker T. alpestre were more aggressive when they were sampled from areas with higher air temperature, and when they had a higher uptake of nitrogen.
There were no correlations seen between aggression and other factors, such as the size of their heads, their relatedness or the particular mix of hydrocarbons in the outer layers of their bodily covering.
As for how they calculated just how aggressive their ants were, this involved setting up one-on-one encounters between ants (1360 in total) in a small space they couldn’t escape, for three minutes.
These encounters were recorded on video, and assigned behavioural categories ranging from grooming each other to ignoring, fighting and even killing. Observations were then fed into established models of calculating aggression amongst animals.
Environmental factors set scene for a ruck
Two of the great concerns on our rapidly-changing planet are rising temperatures and high levels of nutrients such as nitrogen in water bodies and soil (eutrophication) due to fossil fuel burning and use of fertilisers in agriculture. The extremity of changes in both of these is understood to be more severe at higher altitudes, such as where the ant in question lives its life.
Our alpine ants seem to be taking the stresses of climate and habitat change out on each other — but it’s not quite as simple as that.
Higher temperature and nitrogen is likely to mean greater numbers of aphids, producing the honeydew (sugary poo) that ants feed on. In a way, the ants are doing better due to environmental changes, but with food availability can come aggressive behaviour to protect the abundance they’ve got. Higher nitrogen also tends to mean higher protein consumption — another factor that’s been associated with animal conflict — and even greater venom production. The drive to brutality seems unavoidable.
Behaviour matters
The knock-on effects of such behaviour, in this or any other species, could be significant. This might take the form of changing the distribution and habits of populations of this and other species in the ants’ habitats, in response to the increased aggression.
Ultimately, violence can be a good strategy for ants, resulting in the taking of more territory and resources, to the benefit of the colony. But it’s not totally clear cut. Indeed, some colonies in the study were found to be notably peaceful, with the pacifistic approach potentially meaning that more time is spent reproducing rather than getting into scraps.
Extracting wider conclusions from any one study, particularly when it’s looking at one species, is difficult — no matter how tempting it may be.
As such, we can’t say for sure whether the observations in the study would be replicated in other ant species — but a growing body of work now does seem to be suggesting that environmental factors are more important than genetic ones in determining how aggressive ants are likely to be.
What’s certainly true is that the study is indicative of the fact that behavioural impacts need to be considered amongst perhaps more obvious shifts in a fast-changing world.
