In defence of the humble ant, champion of biodiversity
Matt Christmas and Andrew Lowe
You’d be hard pressed to find many people who hold ants in high regard. That might be due to their destructive behaviour towards lawns, their ability to infest your house in no time at all, or a willingness to provide you with a nasty formic-acid-filled bite if you inadvertently step on their nest.
But before we write off ants completely, we should give some consideration to the invaluable work they do for biodiversity.
Several studies in recent years – including this one, this one and, most importantly, this one from 2009 – show ants play a key role in seed dispersal for around 11,000 flowering plant species worldwide.
The ants don’t do this hard work purely out of the goodness of their hearts – they do it for a reward. That reward is a nutrient-rich appendage attached to the seed, known as an elaiosome (see image below), which the ants feed to their larvae.
The benefits to the plant come when the elaiosome has been removed and the seed is discarded among the fertile waste around the ant nest, which provides perfect growing conditions.
Mutualistic relationships between ants and their flowering plant counterparts appear to have evolved independently more than 100 times, with the elaiosome being an excellent example of convergent evolution – that is, different species evolving similar traits or characteristics independently of each other.
The 2009 study mentioned above – by biologist Szabolcs Lengyel and colleagues – shed light on the significance of this mutualistic relationship in terms of the diversification of flowering plant species (it is estimated there are roughly 300,000 flowering plant species on Earth today).
Seed dispersal is vital to the connectivity of plant populations – the greater the distance a seed can be dispersed, the greater the level of connectedness between populations. But ants only transport seeds over very short distances – up to 200m but usually only over 1-2m.
Therefore, any plant relying on ants to disperse its seed will be limited in its ability to spread out over large distances. This limited dispersal distance will lead to geographically isolated populations – the perfect conditions for diversification and speciation.
Indeed, the 2009 study found that flowering plant groups that were ant-dispersed contained more than twice the number of species than closely related species that did not rely on ants for seed dispersal. By dispersing seeds only over short distances, ants have directly assisted in increasing the global diversity of plants.
So, ants have a significant impact when it comes to the diversification of flowering plants. And, with ants outnumbering humans by roughly 1.4 million to one, we shouldn’t be too hasty in writing them off as a pest.
Without ants, the world would lack a lot of the floral beauty we see around us today.Comment on this article
Andrew Lowe receives funding from the ARC and ABRS. He is Professor of PLant Conservation Biology at the University of Adelaide and Head of Science for the South Australian Department of Environment, Water and Natural Resources Matt Christmas is a PhD student at the University of Adelaide
Matt Christmas does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
University of Adelaide provides funding as a member of The Conversation AU.