Urgency is needed to discover and understand life on Earth before many species disappear, writes Professor Toby Pennington
Let’s take a mission to an unexplored planet. No, not a mission by an unmanned rover to Mars. I’m referring to a planet on which we already know life exists – our own.
Of the 8.7 million species thought to live on Earth, only 1.2 million have been described by science. Given the intensity of man-made threats such as habitat destruction and climate change, we are now in a race to describe and understand life on Earth before many species disappear.
It is perhaps not surprising that so many species are unknown, when one considers that many of these undescribed creatures are microscopic. However, tiny creatures, such as bacteria and fungi, do of course play key roles in the ecological processes vital to the planet.
But our planet is a green one. Plants clothe it and drive global cycles in energy, carbon and water: and many plants, especially flowering ones, are not so small in stature. Surely we know all about these herbs, shrubs and trees? Remarkably, we do not. Over the first decade of the 21st century, scientists have been arguing about how many species of flowering plants there are. Today, the estimates vary from 225,000 to 420,000. That is a huge discrepancy of almost 200,000 species.
Why is this? Because our planet’s biodiversity remains unexplored, and opinions differ as to how much is out there. Taxonomists, the scientists who do biodiversity exploration, are largely based in museums and botanical gardens. They have been describing about 2,000 new flowering plant species per year over the past six decades. There is no sign that this rate of description is slowing down – which it would be if we were reaching the end of our task.
The problem is perhaps most acute in the tropics, even for the big trees that form the structural framework of tropical forests. When taxonomists study a group in detail, the result is that 20 to 40 per cent of the species are new.
Going down the size chain, even more description is required. For example, Axel Dalberg Poulsen, now director of the Botanical Garden in Oslo, Norway, recently explored the island of Sulawesi in Indonesia in a research project sponsored by the Sibbald Trust of the Royal Botanic Garden Edinburgh (RBGE). He was searching for new species in the genus Etlingera, a member of the Ginger family. Before his study, it was thought that Sulawesi housed four species of these impressive herbaceous plants. However, Axel found 48 species on the island, including 36 that were new to science.
To put this into context, almost every week a new species is described by scientists at RBGE alone. Although all these new species are ultimately the result of intrepid field research, many are actually not recognised as new species when they are collected. The realisation that they are new to science often happens later when experts subsequently examine the specimens once they are safely preserved in large collections called “herbaria”. The RBGE Herbarium, built up over three centuries, contains three million dried plant specimens. A recent study suggests that half of the new plant species that await description are already stored in herbaria – making them, therefore, a priceless scientific resource.
At this point, one needs to ask the “who gives a toss” question, generally posed to scientists by Radio 4 Today Programme interviewers. Okay, they don’t quite ask the question like that but you can tell they would like to. So, why does species description matter?
One answer would be that you cannot conserve what is not known. The rate of habitat destruction in the tropics is proceeding at unprecedented rates, but how can we indicate priority conservation areas with maximum species diversity if we don’t know what the species are and where they grow? Another response would be that the reactions of plants to climate changes is species-specific. For example, research led by Professor Patrick Meir, of the University of Edinburgh, has shown that some Amazon rainforest tree species are more vulnerable to drought than others. Therefore, understanding the future response of Amazonia – which is known to play a massive role in global climate – to climate change will ultimately depend on knowing what grows where. And we don’t.
Fortunately, the prospects are good for speeding-up the enterprise of taxonomy by harnessing 21st technology. High resolution digital images of specimens can now be freely shared and species-specific DNA sequences – analogous to supermarket barcodes – can help to define species. We can – and must - win the race to understand what the world’s species are to enable us to conserve and manage our planet’s resources.
• Professor Toby Pennington is head of tropical biodiversity at the Royal Botanic Garden Edinburgh www.rbge.org.uk