Yes. That’s ONE TRILLION. ‘Possibly’ – as recent research using statistical scaling rules shows Earth’s total biodiversity, expressed in numbers of species, lies somewhere between 100 billion and (possibly more than) ten times as much. Welcome to the world of microbes.

Predicting total Earth biodiversity from scaling laws for macrobes and microbe species.

Part of understanding the possible impact of the pending Holocene-Anthropocene Mass Extinction is of course understanding how high Earth’s biodiversity actually is. Generally we humans, a relatively large and heavy mammal species, focus on the larger life forms around us. Other mammals for instance, like that dog on the couch.

We tend to ignore the fact that that warm, often happy and indeed surprisingly loyal unit of living biomass is apart from one single Canis lupus familiaris also very many other species. The reason is simple: we can’t see all those friendly little bacteria, fungi and other microorganisms. That’s why it’s also very hard to count them.

Applying macrobe scaling laws to microbe biodiversity

Counting does work for other groups of organisms though – larger organisms, macrobes. As we’ve seen in part 2 of this biodiversity series, for instance the documented total biodiversity for mammals lies at 5,487 species; 8,734 reptile species; 9,990 bird species; about 11,000 different mosses, some 12,000 ferns (pteridophyta) and 223,000 to 420,000 different species of flowering plants.

Now according to a study by two Indiana University researchers that was published in PNAS last year some patterns of prevalence of these larger species also apply to microbe diversity. Investigating an Earth biodiversity inventory of about 5.6 million species collected from 35,000 different sites they find that scaling rates for ‘commonness’ and ‘rarity’ for microorganisms and macroscopic plants and animals are similar. From this a universal dominance scaling law is deduced that holds across 30 orders of magnitude, predicting the abundance of dominant ocean bacteria and leading to a total estimate for Earth’s biodiversity of upwards of 1 trillion (microbe) species.

We thought this is a good starting point to assess possible climate change-induced biodiversity loss, which we will do in the upcoming chapters of this series. Because before we count what we might lose we must first count what we actually have. Will the Holocene-Anthropocene Mass Extinction bypass the world of microbes – while decimating larger life forms? Possibly. But there is biodiversity at an ever smaller scale: intraspecific biodiversity (gene diversity) – and we do already know that also this intraspecific biodiversity might sharply decline due to climate change.

To be continued…

© Rolf Schuttenhelm | www.bitsofscience.org