Ever wondered why ant colonies are so big? One talks about millions of individuals in some colonies. And for people working on invasive ants, like us, this thought can be both fascinating and frightening (BTW, we work on invasive ants, because they are importants. Sorry.). Take the Argentine ant for example. It forms “supercolonies” (related colonies) that can encompass tens of thousands of nests over thousands of kilometres. This amounts to perhaps hundreds of millions of tiny, mean brothers-in-arms that will attack and effectively kill almost anything they encounter and that is small and stupid enough to hang around. Sweet little things. We love them. Later on, I’ll tell you how we compare the nastiness of the various invasive ant species, and believe me, Mother Nature had loads of fun – and bursts of creativity – when She created ants.
But for now, how did they manage to evolve such immense social colonies? One answer could come from our study of Allee effects. An Allee effect is a positive relationship between the size of a population and its capacity to persist and grow. In a word, in some species, the more individuals there are, they better they do, often because they help each other in some various ways. So, we studied Allee effects in ants; just because we study all we can about the Allee effect (because we are a bit monomaniac) and because we like ants. We like rhinos too, but that’s less practical in a lab. Oh, and of course because, very surprisingly, nobody ever had the idea (or the madness?) to look into that.
So, we set up large experimental designs to record the survival and reproduction of colonies of various sizes. By various sizes, I mean different number of workers and different numbers of queens. Because, yes, some ant species live with several (sometimes hundreds of) queens in the same nest. And after a few years of hard work, the results were worth it: there are indeed Allee effects in ants; at least the two species we studied. The corresponding paper is here. The more ants, the better they do. And it even gets better: the more queens, the more workers are produced per queen (that’s not that obvious, they could compete for food). And also, the more queens, the better the workers survive (don’t ask me why, I’m supposed to be concise here). And the fun continues: the more workers, the higher the queens productivity! So in fact, each cast (workers and queens) benefit the other cast, so that it creates a mad feedback loop leading to ever growing colonies (that I think can possibly only end in them taking over the world). So this mechanism of Allee effect might have played an important role into making large colonies of eusocial species. Nice no? Oh, come on!
What, no funny image? Yes, this one IS funny too, just watch closer!
Biodiversity Dynamics 