How many species are there?

How many species are there?

“The general public are identifying with these entities they call species and they think they’re real biological, natural units rather than being a slice in time that is a human construct,”

Stephen Garnett, Professor of Conservation and Sustainable Livelihoods, Charles Darwin University, Australia

This is a quote from the lead author of a project to create a universal species list. The idea is for a single classification system to end centuries of disagreement and improve global efforts to tackle biodiversity loss.

There is no definitive list of species!

Yes, staggeringly this is true. There are competing lists for some of the colourful creatures such as birds and no list at all for some of the more obscure or less charismatic groups of organisms. And this has been the case ever since humans decided to classify organisms using a particular form of biological classification (taxonomy) set up by Carl Linnaeus in his Systema Naturae (1735). Yep, we agreed on the system close to 300 years ago but still do not have a definitive list.

There is a lot of diversity in nature. This means a complete catalogue is huge and requires a great deal of cooperation among scholars and jurisdictions. Remember a lot of collecting went on in colonial times meaning that much of the biological source material (specimens) are not in the countries where they were collected.

Then there are groups of organisms that not too many folk are interested in — nematodes, biting flies, dung beetles, slime moulds, viruses — and those that are inaccessible to all but the very brave — gut parasites of elephants, deep-sea fish, cave-dwelling insects.

And then there are few experts with the skills to make formal identifications and describe new species, especially for the obscure groups of organisms.

These are just a few of the reasons why what we used to call an All Taxa Biodiversity Inventory or ATBI does not exist at the global level.


Back in the day, over 25 years ago, I used the All Taxa Biodiversity Inventory concept as a practical class for undergraduate biodiversity students.

We designated a parcel of land, lined up some sampling equipment and told the students to go measure biodiversity.

They looked at me blankly. Many were quite frightened.

‘You are kidding right” was usually the response.

“No, not kidding. Get your heads together and figure it out.”

“But what do we measure?” they said.

“Everything, it’s not called all taxa for nothing”

“What? Microbes as well??

“All taxa.”

“But we don’t even know what a taxa is?”

“Ah-ha. Perhaps that is the first problem to solve. What level of taxonomic resolution should be used to catalogue biodiversity”

“Species obviously,” they said.

“Very well, then, off you go, go measure an all species biodiversity inventory.”

That a generation on from these confused undergraduates we still do not have a global list of described species let alone the details of what taxa might occur in any one location is an indictment.

That we are still arguing over the definition of species when, ever since the term was invented, everyone realised it was only a loose description that applied mostly to sexual heterotrophs.

“You have a species or you don’t, you have a subspecies or you don’t. And you impose this discrete binary system on a continuous process of evolution. There’s bound to be trouble.”

Frank Zachos, Professor and Head of the Mammal Collection, Natural History Museum of Vienna

This just shows how good we are at fiddling while Rome burns — to be busy doing unimportant things when you should be dealing with an important problem — noting of course that Emperor Nero could not have fiddled at all in as the instrument had yet to be invented although he played the cithara (a type of lyre). Close enough.

What’s the important problem we should be dealing with?

Biodiversity loss.

And not for the reasons that usually come to mind. It is not the loss of the rare, the endangered, or the iconic that natters. What matters is the loss of what biodiversity does in landscapes. The contribution organisms, and explicitly the diversity of organisms, make to the services we need for human existence — clean air, clean water, nutrient exchange, decomposition, pollination, feel good, etc.

It is a long list.

We are losing what biodiversity does when we oversimplify landscapes to channel production into the food and fibre we need. Only the gains in efficiency are temporary when the resource base changes, the climate shifts and nature’s services are stretched.

They are only maintained for the long haul by diversity.

The ATBI for the students was a way to help them understand, as is a global inventory of species; a way to understand how much diversity there is and how much of it we need to keep.

Nature does not care a jot about this but we should.

She will bounce back but it might be after we are gone.