ELI5- how do scientists know that a particular species’ (panda, turtle, sharks, tigers) population is getting extinct?


ELI5- how do scientists know that a particular species’ (panda, turtle, sharks, tigers) population is getting extinct?

In: Earth Science

They do studies to see how many of that animal there are in certain areas, and try to extrapolate outward from there. For example, if you know pandas can only live in bamboo forest, and you survey some random bamboo forest and find 1 panda per square mile, and you know there’s only 100 square miles of bamboo forest left, you can make a guess that there probably aren’t much more than 100 pandas.

Along with other commenters on statistical means of counting populations (pop. to area extrapolation) another method has to do with habitat loss or degradation. I mean – it’s the same kind of calculation, just different.

For example, let’s say there is a species of small mammal (like the pika) that can only thrive at a certain altitude and with a certain species of tree at that same altitude. Let’s further say that due to climate change, that altitude’s temperature is changing and the specific trees are no longer propagating or growing at the rate necessary to sustain a healthy population of pikas. Therefore, you can deduce that the pikas are in danger because their very limited critical habitat is growing smaller (without having to count pikas).

Same can be said for many marine habitats, such as coral reefs. Polar bears have similar issues, as do many bird species (especially those in rainforests). Predator cats (like mountain lions) need HUGE areas when it comes to range. If a significant portion of that range is lost, it’s a massive problem for the cats.

Another method, which is more genetic-based:

Most (not all, but most) species required what is called heterogeneity. They need a diverse gene pool to stave off illness, inbreeding and other genetic weaknesses.

For example, the last known wild population of black footed ferrets were captured and have been bred from about 30 survivors up to a few hundred (I think, not sure on that number, but a significant number compared to where they were). Which is awesome! But with such a limited gene pool things are still very grim for the ferrets. That’s why when a ferret was recently born from a type of cloning of a previously deceased ferret – this was big news, because this ferret will add to the diversity of the gene pool.

This is also a big issue for Yellowstone grizzlies. They have a fairly stable population (well, they have other issues but anyway) however they are completely cut off from any other existing populations – the rest of the grizzlies for the most part are in Canada. Consequently the Yellowstone grizzlies have a serious case of a homogeneous gene pool.

Did y’all hear about the manatees? Because of the weirdness of the weather lately, apparently 403 manatees have died so far in 2021 😞