Edit: 🤦🏻♂️ What a fail of a title. What I meant was…
How do we know what the population of animals are?
In: 7
how do we title gore?
How do we know how they what? Is there supposed to be more to this question?
Estimates. You don’t count every grasshopper in a field, instead you count how many grasshoppers in a 1 foot square and then multiply that number by number of square feet in field. You can further multiply number of fields for entire planet if desired.
Edit* some populations, like tigers, are so small near every individual can be counted.
One way of estimating population size is to catch a group of the animals, tag them, and then release them. Now the proportion of tagged animals in the wild is Tagged / Population
If you return some time later and catch another group, and count how many of them are tagged, you can presume this proportion is the same as the proportion before. And from that you can estimate the population.
The method I was taught in school was thus:
You go out and capture, at random, 20 kangaroos. You put a tag on all of them, then let them go. A few days later you capture another random 20 kangaroos. What percentage of the second batch are tagged? You can then extrapolate how many kangaroos there are in total using this percentage.
For example, if there were 5 tagged kangaroos in the second batch, that’s 25% of the total. We can then assume that the first batch was 25% of the total population. Thus, we estimate that there are (20 x 4) 80 kangaroos in this area.
Alternatively, lets say there was 2 tagged kangaroos in the second batch. That’s only 10% of the total. We would then say that the kangaroo population in this area is (20 x 10) 200.
[This page](https://thirdspacelearning.com/gcse-maths/statistics/capture-recapture/) goes into more detail on the maths involved.
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