How ants invented fynbos

2012-10-29 15:00

Andreas Späth

Nerdy Captonians like myself derive a lot of silly satisfaction from ridiculing assorted European tourists for their countries' botanical inadequacies by pointing out, for example, that there are more different types of plants in the Cape Peninsula than in all of the British Isles combined.

It’s an easy game to play when you live in the Cape Floristic Region. Crammed into the southern corner of Africa, it might be the smallest of the world’s six floral kingdoms (the others all cover entire continents), but with well over 9000 plant species of which 69% occur nowhere else, it packs a considerable biodiversity punch.

But exactly how did this amazing plant variety come about in such a small area? “Evolution” is the obvious answer, but there’s more to the story.

In 1978, the maverick American palaeontologist Robert T Bakker came up with what I’ve always thought of as a very attractive theory (you'll have to pay to read it) to explain the astonishing proliferation of so-called angiosperms, or flowering plants. He suggested that dinosaurs had “invented” them.

In the early stages of the dinosaur era, the world was dominated by gymnosperms, a group of plants that includes conifers, cycads, Ginkgo trees and Namibia’s weird Welwitschia. The fossil record shows that by the time the dinosaurs became extinct at the end of the Cretaceous period about 65 million years ago, gymnosperms had been displaced almost everywhere by the angiosperms, of which there are now somewhere between 250 000 and 300 000 distinct species.

Bakker argued that flourishing herds of ravenous herbivorous dinosaurs mowed down gymnosperms wherever they could find them and that their intense ground-level feeding habits opened up space and opportunities for the fast-growing and innovative angiosperms to spread and diversify.

It’s a lovely piece of geo-poetry, but alas, it’s not true. Research conducted during the last three decades has shown that there is very little concrete scientific evidence to suggest that a vegetarian dinosaur feeding frenzy had anything to do with the origin or dispersal of the angiosperms. Dinosaurs didn’t invent flowers... or fynbos.

For that, it would seem, we have to look at the opposite end of the zoological size scale. Scientists now believe that ants may have played a crucial role in creating the astonishing variety of flowering plants in the Cape.

Many fynbos species have developed a little appendage called an elaiosome on their seeds. The only known function of this fleshy structure which is rich in proteins and fats is that it attracts ants who carry the seeds off to their nests where they eat the tasty morsel or feed it to their larvae.

The discarded seeds are of no interest to the ants and are buried in the nest’s waste disposal area, which, because it’s full of faecal matter and other organic ant refuse, is essentially the equivalent to a fertile compost heap.

Here, the fynbos seeds are protected from fires and other critters that might want to eat them, and they have a much improved chance of germinating than elsewhere in the nutrient-poor, sandy soils of this region. It’s a beautiful example of co-evolution and mutualism, the process in which the interaction between two different species is beneficial for both.

Seed dispersal by ants even has its own name: myrmecochory. It leads to genetic isolation by separating seeds from their parent plants, as well as higher survival rates, both of which contribute to increasing diversity. According to Ladislav Mucina and Jonathan Majer of Perth’s Curtin University of Technology, “myrmecochory may have resulted in a doubling of plant diversification” among the angiosperms.

So what’s the point of me telling you this little story? It’s to:

a) encourage you to pay some respect to the tireless little workers next time you step on an ant (don’t worry too much though – there are an estimated quadrillion of them alive on earth at any one time);

b) show you that evolution isn’t all about red-in-tooth-and-claw competition – cooperation plays an extremely important role; and

c) impress on you that we’re busy destroying biodiversity within decades that it took nature (and countless ants) millions of years to create – the Cape Floristic Region is under severe stress from climate change and habitat-loss through human activities.

- Andreas freelance writer with a PhD in geochemistry. Follow him on Twitter: @Andreas_Spath

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