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Course: High school biology - NGSS > Unit 9

Lesson 1: Biodiversity

Creative thinking in science: exploring biodiversity

Practice creative thinking while exploring Earth's biodiversity.

How many species are there?

Earth is teeming with life, from microscopic single-celled organisms to huge, lumbering elephants; from cuddly cats to ferocious great white sharks. All of this variety has a special term which you may have heard before: biodiversity. Put simply, biodiversity describes the variety of life on Earth. Measuring aspects of biodiversity is important for understanding the health of Earth and its ecosystems, and scientists do it all the time.

Let’s imagine that you are an ecologist looking into Earth’s current level of biodiversity. One component of biodiversity is species number. So, the question you are tasked with answering is:

How many species currently exist on Earth?

Wait, wait, wait…that seems like an impossible question to answer! There are so many different kinds of organisms. How can we possibly count them all? Well, we have to start somewhere. Let’s try this: how many species can you list in one minute? Grab a piece of paper, a pencil, and a timer, and give it a try!

How many species did you list?

Your list is probably quite long! But, it likely only scratches the surface of Earth’s true biodiversity.

What types of organisms are on your list?

Your list may include mostly animals because those are the organisms that most of us are familiar with. But, what about plants and fungi? Did you think about bacteria, or other organisms that aren’t visible with the naked eye?

How did you approach the question?

Did you list organisms you’ve seen around your house or in a zoo? Maybe you thought about the species in one or two types of ecosystems that you are familiar with. But, what about the species that live deep in caves, or near hydrothermal vents at the bottom of the ocean? Would your approach allow you to account for species that haven’t even been discovered yet?

Are your brain juices flowing yet?

We hope so!

Ok, so it seems like listing species one by one is not the best approach to answering the question “How many species exist on Earth?”. To answer this question, we’re going to have to think creatively.

What is creative thinking?

When people think of creativity, they often think of art, music, or literature. However, creativity includes ways of thinking that are important in the sciences, too!

For example, creative thinking can include problem solving, coming up with new and useful ideas, taking risks, embracing contradictions, or thinking about natural phenomena in abstract and simplified ways. Scientists also have to communicate their findings, which can take on more traditional forms of creativity, such as visual design.

Let’s use creative thinking to answer the question!

There are potentially many creative ways to approach answering our question. One of these approaches is called a Fermi estimate. A Fermi estimate is a method of breaking one large, complex problem into many smaller, more manageable ones. This method allows a person to estimate a quantity that at first seems difficult or impossible to calculate.

To illustrate how to approach a Fermi estimate, let’s consider a classic Fermi question: how many piano tuners are there in Chicago? To arrive at an answer, we can approach the estimate as a series of steps: first we can estimate the population of Chicago, then the number of households in the population, then the fraction of those households that would have a piano, then how often those pianos would need to be tuned, and so on.

By considering the answers to these smaller questions, we can arrive at an approximate answer for our big picture question, which at first seemed nearly impossible to answer.

Now it’s your turn to use a Fermi estimate to answer the question of how many species exist on Earth. Grab another piece of paper, a calculator, and your creative brain, and start estimating!

First, try breaking the question down into smaller, more manageable questions. For example, you might list different types of ecosystems on each continent and estimate species numbers for each.
To help with your estimates, draw on your own knowledge. Think about the ecosystem outside your door. Or, think of one that you have visited, such as a local or national park. How might you determine the number of species there?
Try turning off the “error-checker” part of your brain. Let yourself come up with as many ideas as you can. There are no wrong answers. It’s the process of thinking through the problem that is important.

What is your estimate?

Nice work! You have come up with an estimate for the number of species on Earth. Next, discuss the following questions with your classmates, friends, or post your answers in the comments section below:

How many species did you estimate to be on Earth?
How did you arrive at that number?
Did any tricky issues come up as you worked out your estimate?
What assumptions or limitations did you have to make?

You may not have realized it, but as you were coming up with your estimate, you were thinking creatively! You thought of novel ways to approach a problem, you embraced uncertainty, and you allowed yourself the opportunity to brainstorm freely. Did you know that many professional scientists have used creative thinking to answer the same, or similar, questions about Earth’s biodiversity?

Erwin’s estimate: 30-100 million arthropod species on Earth

In the 1980’s, a scientist named Terry Erwin sprayed pesticides into the leaves of a tree in a tropical forest and counted the more than 1,000 species of beetle that fell to the ground. Of these, Erwin determined that 163 of these species were found only on that type of tree. Using this information along with tree species estimates, estimates for the number of ground-dwelling beetles, and the estimate that beetles make up roughly 40% of all arthropod species, Erwin came up with a final estimate of between 30 and 100 million arthropod species on Earth.

Mora et al.’s estimate: 8.7 million eukaryotic species on Earth

In 2011, a team of scientists estimated the number of eukaryotic species using the taxonomic system by which we classify organisms. This system organizes species into genera, genera into families, and so on all the way up to the level of domain. The scientists found numerical patterns within this taxonomic system, which allowed them to use documented numbers from the higher taxonomic groups to predict the number of species. They came up with an estimate of 8.7 million eukaryotic species on Earth. If this estimate is accurate, then 86% of eukaryotic species on Earth have yet to be discovered!

Locey and Lennon’s estimate: 1 trillion microbial species on Earth

In 2016, scientists brought together many datasets from various sources, which provided information about real communities of microscopic and non-microscopic organisms. Using this data, the scientists found trends in how species number scales with the number of individuals present in a community. Using this scaling law, they predicted that Earth contains 1 trillion species of microbes!

How do these scientists’ estimates compare to your own?

References:

Erwin, Terry L. “Tropical Forests: Their Richness in Coleoptera and Other Arthropod Species." The Coleopterists Bulletin 36, no. 1 (March 1982):74–75.

Mora, Camilo, Derek P. Tittensor, Sina Adl, Alastair G. B. Simpson, and Boris Worm. “How Many Species Are There on Earth and in the Ocean?” PLoS Biology 9, no. 8 (August 2011): e1001127. https://doi.org/10.1371/journal.pbio.1001127.

Locey, Kenneth J., and Jay T. Lennon. “Scaling laws predict global microbial diversity.” Proceedings of the National Academy of Science 113, no. 21 (May 2016): 5970-5975. https://doi.org/10.1073/pnas.1521291113.

Let’s get visual

Now that you’ve answered a very difficult question, here's a simpler one for you: can you identify at least ten different species in a park or other ecosystem near you?

Draw each species using pencils and paper, a digital illustration tool, or by some other means. Describe the characteristics of each species. Think about what the biodiversity in your area means to you.

Want to join the conversation?

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Empress Samirah
Posted a year ago. Direct link to Empress Samirah's post “.) How many species did y...”
.) How many species did you estimate to be on Earth?
About 2,000,000! 2 million.
.) How did you arrive at that number?
I looked up the number of species per each of the 7 continents, and then added them all up. I also added the number of deep sea animals and plants!
.) Did any tricky issues come up as you worked out your estimate?
A lot of the numbers were very rough, or would only account for the number of birds, so I’d have to look up the other numbers too.
.) What assumptions or limitations did you have to make?
The number is definitely going to bigger than my guess, because we just don’t know!
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Vic Johnson
Posted 2 years ago. Direct link to Vic Johnson's post “what is something that yo...”
what is something that you wouldnt allow to happen
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- MagicalPotato
  Posted a year ago. Direct link to MagicalPotato's post “The extinction of animals”
  The extinction of animals
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❄️ArticWolfe17❄️
Posted 2 months ago. Direct link to ❄️ArticWolfe17❄️'s post “I definitely can list mul...”
I definitely can list multiple animal species before one minute!:)
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