It's called a model Craig.
This is so much in my wheelhouse that I'm going to have to do a modelling thread aren't I? I hope you're all excited ^_^
Bear with me I'll get on it shortly.
Bear with me I'll get on it shortly.
Right: welcome, gather round all.
Let's talk projections.
Projections are really important in science. As our man Craig points out - we can't spend the time counting every single thing that's out there. It would take a reeeaaally long time, and often it is hard to find.
Let's talk projections.
Projections are really important in science. As our man Craig points out - we can't spend the time counting every single thing that's out there. It would take a reeeaaally long time, and often it is hard to find.
This goes for living things, which this thread will focus on because that's the example in question and my area of expertise - but it also goes for other things like stars in the universe, and money.
Conservation scientists often get criticism of our population projections but economics relies very heavily on similar projections - but we rarely hear people like 'just found out the head of the Bank of England didn't count all the money, they estimated it on a computer!'
So how do us ecologists and scientists go about quantifying how many of x animal has died, or how many of x animal still exist?
Well the answer is we count some of them and use models to do the rest (unless there's <~500 left and we know where they all are e.g. kakapo)
Well the answer is we count some of them and use models to do the rest (unless there's <~500 left and we know where they all are e.g. kakapo)
Interlude while I go find that great gif of how mark recapture models work. Will resume shortly.
So one way of doing this is to catch some animals and tag them, then you catch some more animals at a later point and look at how many in the second group are tagged. It's called capture mark recapture for fairly obvious reasons.
This can be used to estimate population size as the number tagged in the 2nd group should be proportional to the number of tagged in the population. So you can divide the total number tagged by the number of tagged individuals in the 2nd sample to get a population estimate.
This is a really simple way (mathematically, actually catching and tagging the animals can be really hard 😂) of doing it but there are lots of improvements + additions to these models which make them more complicated and give better estimates.
Like for example assumptions about population size + structure!
Here is a cool illustration of how this works in gif form:
Here is a cool illustration of how this works in gif form:
There's also distance sampling. This is really good for when you are having to use transects (walking or driving in a straight line or standing in one spot) and there's lots of trees and stuff blocking your vision either side.
It basically assumes that the further away an animal is the less likely you are to see it. Then again some relatively simple maths is used to take how many animals you saw on your transect and turn it into your population estimate.
There are a whole bunch of other ways to do this that I won't go into but you can also do stuff like send up a drone and use an algorithm to count animals from a photo, build matrix based population models, or extrapolate from camera trap photos etc
In our man Craig's example the scientists used these population estimates, from published studies, and the area of habitat lost to give an estimate of the number of animals that died.
Habitat lost in hectares x number of animals per hectare = number of animals that died.
Habitat lost in hectares x number of animals per hectare = number of animals that died.
To say it's a computer generated number is misleading and designed to make it look scary and removed from reality. Many of us in conservation biology could sit you down and walk you through the estimates using a calculator.
And to say it's not grounded in reality is simply not true. It's based on actual observations. It may not be accurate to single, or double, or triple digits but it's a reasonable estimate.
Chris Dickman (who did the original estimates) is an expert in doing this stuff.
The estimates don't include invertebrates.
We don't need to count every dead animal (and couldn't!) to be able to communicate the enormity of the crisis.
Over a billion animals are dead.
The estimates don't include invertebrates.
We don't need to count every dead animal (and couldn't!) to be able to communicate the enormity of the crisis.
Over a billion animals are dead.
And for anyone who thinks I mostly write about farts this stuff is my day job so I'm always happy to chat about it 😊
So thanks Craig for giving me the opportunity!
Take home: modelling isn't scary. Climate change is.
So thanks Craig for giving me the opportunity!
Take home: modelling isn't scary. Climate change is.
