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The diversity of life on Earth: A quest by Ashiq PP

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    • Have you ever wondered about the variety of sounds that you hear when you step into a forest?
      • All those chirping, humming and calls, what are they? Where are those subtle and sharp voices coming from? Have you ever seen a drop of pond water under a microscope? The vast array of life forms that forges those structures!!

The Quest

This is an article emphasising a quest towards the finding and cataloguing the species of life around us. The new articles will be published one the author finishes them.

a study on diversity of natural species | padanam.in blog

Microcosm to Macrocosm

Why is it that we have organisms as big as a blue whale and as small as a Mycoplasma?

It is recorded that blue whales can reach upto a length of 30 metres whereas a Mycoplasma can be as small as one millionth of a metre(micrometer). Don't forget about all those beings that lived on earth in the past, starting from the microscopic autotrophs that paved the way for all other life on earth to the mighty Dinosaurs. 

But do we know how many living beings there are on earth? Do we know how different are they from each other? 

The sad truth is that we still don't have a clear idea about how many types of living things or that we call species there are on earth presently, let alone those that have gone extinct. Why is it so difficult to determine the number of living beings? The practical problem is that many of the organisms live in harsh and inaccessible habitats like the deep seas or that many are parasites living inside other tiny animals or that most of them are microscopic organisms.

There have been many attempts to know the number of species on earth. How is it possible to know the extent of diversity on earth if we don't know all the species that inhabit the earth? That is where scientists employ patterns of diversity. They looked at the diversity of organisms currently discovered and based on that arrived at a pattern and extrapolated it to understand the range of diversity. It is like saying the number of species that inhabits the earth cannot be determined specifically, however, we can determine a range or an estimate to the number of species.

The crazy experiment

In the 1980s, Terry Erwin, an American Entomologist did something crazy and at the same time insightful. He sprayed the canopy of some trees in a rainforest in Panama with pesticides. Of all the insects that fell down, his target was beetles. He collected the beetles that fell off from each tree and found that a single tree hosted as much as 163 species of beetles. 163 types of beetles!!!

Since he knew that beetles are the most diverse group of animals with about 40% of all the discovered animals (he knew that because he is an entomologist. Phew, he was lucky!!), he extrapolated the number and somehow estimated that there will be about 30 million species on earth!!

Many scientists thought that was too high an estimate to be practical. Recent estimates are about 10 million species, excluding microbes that require sequencing their DNA to distinguish between strains. 

Eukaryotic data stream

A 2011 study published in PLoS narrows down the number of eukaryotic organisms to 8.7 million species. With 6.5 million species on land and 2.2 million in aquatic habitats, the study concludes that about 86% land species and 91% marine species are yet to be discovered. How cool is that?? (I mean, for a taxonomist, it's a lot of interesting work to do!!) The paper states that there is a consistent pattern in the hierarchy of classification which can be scaled to predict the number of species. In other words, the number of species is always higher than that of genus and there will be more genera than families. This scaling pattern was helpful in estimating the number of eukaryotic species.

Prokaryotes like the bacteria are also important and their diversity has to be estimated. Since understanding their diversity requires sequencing their DNA, it is very time consuming. 

A 2016 study published in the Proceedings of the National Academy of Sciences states that there are a total of 1 trillion species on earth after taking microbes into account. They collected a huge data set of 20,376 sampling efforts of bacteria and 14,862 sampling efforts of other organisms such as plants, mammals, invertebrates which was publicly available and then came into this conclusion of staggering 1 trillion species. 

The lead author of the 2011 study, Camilo Mora, a marine ecologist at the university of Hawaii emphasizes the need to know about the number of species that inhabit the earth as it addresses many basic questions of science and conservation. We cannot conserve all the biodiversity on earth if we do not know how big that diversity is!! We cannot form policies if we do not know how many species are to be considered. Thus understanding how many species are we cohabitating with is the basic scientific curiosity.

About the author

This article was written by Ashiq. PP; The author is a Junior Research Biologist a Salim Ali Centre for Ornithology and Natural History (SACON), Anaikatti Coimbatore. The author has a Post graduation in Zoology from University of Madras and took Bachelors degree in Zoology from University of Calicut. The author is also one of the founding authors of Padanam

References:

  1. Kenneth J. Loceya, and Jay T. Lennona. Scaling laws predict global microbial diversity. PNAS, 2016 DOI: 10.1073/pnas.1521291113
  2. Camilo Mora, Derek P. Tittensor, Sina Adl, Alastair G. B. Simpson, Boris Worm. How Many Species Are There on Earth and in the Ocean? PLos, 2011 https://doi.org/10.1371/journal.pbio.1001127
  3. Robert M. May. Why Worry about How Many Species and Their Loss?. PLoS, 2011 https://doi.org/10.1371/journal.pbio.1001130
  4. Theconservation.com
  5. Nature.com
  6. Sciencedaily.com

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