The Earth’s Biodiversity Could Be Much Greater Than We Thought

How many species of frog are in the picture? Genetics often says ‘more than we thought’. Michael Lee (Flinders University & South Australian Museum), CC BY-NC

The ConversationAfter centuries of study, you’d think we’d have at least a rough idea of how many different species of life exist on Earth. This is becoming even more pressing as biodiversity disappears at an increasing pace due to human impacts. Some species are going extinct even before we discover them.

Scientists have named nearly 2 million species, but the estimated total number out there has ranged from 3 million to 100 million. Consensus recently congealed around the lower end of this range, with one widely touted study proposing a precise figure of 8.7 million species (excluding bacteria strains, which are too tricky to count).

If so, we’ve made sizeable inroads into cataloguing the planet’s biodiversity, with perhaps 20% done.

But in correspondence published in Nature this week, we suggest this consensus may underestimate the Earth’s biodiversity by a factor of ten.

If so, the task of describing and understanding biodiversity is far more Herculean than ever imagined. In the 300 years since the Swedish naturalist Carolus Linnaeus pioneered scientific classification, we might have managed to recognise only 2% of Earth’s biodiversity.

Species Are Often Not What They Seem To Be

Species are one of the fundamental units of biodiversity. Each species represents an independent evolutionary lineage and irreplaceable gene pool.

For example, the domestic dog, Canis lupus, is a separate species from the golden jackal, Canis aureas, since these two groups do not normally interbreed nor exchange genes. But spaniels and dalmatians are merely different breeds of the same species, Canis lupus, which can readily get together to produce mongrels.

Sometimes different species can be hard to tell apart. An extreme case involves cryptic species. These are separate species that are very similar outwardly, yet are true species that never interbreed. They thus possess distinct gene pools evolving in independent directions.

DNA from the tiny Clawless Gecko Crenadactylus from northern Australia shows it was not one but at least ten different species; eight are shown here. Brad Maryan (Western Australian Museum), Glenn Shea (University of Sydney), and Glenn Gaikhorst

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