This sort of statement has always fascinated me: *”There are thought to be approximately 160,000* *species* *of moth,* ***many of which have yet to be described.****”*
How do we (well, “they”) ascertain what percentage of the total count are those we *haven’t* yet found?
(Note: I couldn’t find anything like this in posts containing “species” in the last year or so, so apologies if this has been answered further back).
In: 10
It’s a guess.
The classification we have has gaps. We can see how many genes are different between the known species, and the closest species are X genes different. Then for every gap that’s 10X we presume there are 9 missing species. Maybe they are extinct – but we don’t see them in the historical record. We don’t know, maybe we just haven’t found them.
It’s really just an estimate with a lot of different factors to consider. In college ecology, I was told that one of the biggest clues is to look at the rate of species discovery in specific areas where field work is being conducted. Because you’ll start with a huge discovery boom, and the longer you keep cataloging, the lower chance you have of finding new things. Slap some trajectory lines on the rates and hope they reflect reality.
You can also make very rough guesses for completely unexplored regions by looking at surrounding data; if sectors A, B, and C of a rainforest each have 20 species of moth unique to that sector, it’s a reasonable guess that unexplored sector D might have 20-ish too.
This is closely related to something called the [German Tank Problem](https://en.wikipedia.org/wiki/German_tank_problem).
In WWII the Germans use sequential serial numbers, so some enterprising statisticians realized they could make an informed guess about the total number of tanks based on the numbers from the *observed* tanks.
Of course, part of your estimate has to include the number of observations (or tanks destroyed).
Species estimation is done in a similar way. For a given intensity of study, how many species did we find? If we find a ton in one survey, we can make an estimate that the biodiversity is exceptionally high and build an estimate around that.
For an interesting take on some of the math, see [here](https://www.pnas.org/doi/10.1073/pnas.1607774113)
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