How do you know that 90% of species are undiscovered if they are undiscovered? how do you know they are there if you haven’t discovered them yet?

Question

Everyone keeps saying its like a list, how does that work?? Do you have like a pokedex where the undiscovered species appear in grey or something like that???

In: Biology

Answer 1

Biologists have a trick for figuring out how many of something exist without counting them.

Let’s suppose you want to know how many butterflies there are in a forest. You could capture them all and count them, but that would be very difficult, and it would probably be bad for the butterflies, for the things that eat the butterflies, for the things the butterflies pollinate, etc, etc.

What you do instead is you get yourself a little paintbrush and some paint, and you start catching butterflies. Each time you catch one, you do one of two things :

1. If the butterfly is unmarked, you paint a tiny dot on it, release it, and write a “X” in your notebook. This a new butterfly.
2. If the butterfly is marked, you release it, and write a “O” in your notebook. This is a butterfly you’ve seen before.

When you start, every butterfly will be a new butterfly. If you continue, eventually you will see more and more butterflies that you’ve already seen. If every butterfly you see is marked, then you know you’ve caught every butterfly. But it isn’t necessary to go that far. In fact, you can probably stop after you’ve marked just a handful of O’s.

Next, you get a big piece graph paper and you make a plot. For each mark in your notebook, you move one space to the right. Each time the mark is an X, you move one space up. So, the horizontal is the total number of butterflies you caught, and the vertical is the cumulative number of new butterflies. It will start out looking like a straight diagonal line, but will gradually start bending into a horizontal line. The curve will be a little bit noisy, but you know that two things about it that must be true :

1. The curve must stay below a ceiling equal to the size of the population
2. The size of the population is the only parameter that affects the shape of the curve

So, as soon as you can see the curvature of the line, you know what the size of the population is. It doesn’t actually matter how slight the curve is — you only have enough observations to measure it.

This is called a [Mark and Recapture](https://en.wikipedia.org/wiki/Mark_and_recapture) experiment. There is a related approach for counting species called the [Collector’s Curve](https://en.wikipedia.org/wiki/Species_discovery_curve).