Extinction

mass extinctions are widespread, rapid decreases in the earth's biodiversity. And there are five that are thought to have occurred in the past, including the ever famous one that wiped out the dinosaurs due to a meteor, though actually, the asteroid that hit the Earth was thought to be about the size of Manhattan. So probably be a heck of a lot bigger looking than that. Now, we are actually in the midst of 1/6 mass extinction known as the Holocene extinction. And not gonna not gonna split hairs here. It's due to human activity. In part. You can see this trend in this chart here, which looks at the amount of large mammals that remain in areas after humans have gotten there. So you can see, uh, where humans have entered the scene with these arrows. And in Africa, there wasn't as much of a diminishment of the number of large mammals. But you can see that in Australia, in North America and on Madagascar, there was a huge drop off. And it's theorized that this is due to the fact that you know, when humans show up, they're still hunter gatherers, and they're going to hunt these large mammals, which we're gonna provide lots of food to the brink of extinction. And once they really exhausted that resource, that's when humans would finally, um, you know, settle down and form more agrarian societies. Of course, not everyone did their. You know, we're still tons of hunter gatherers, but it's just part of the trend. You know, wipe, eat all the big animals and when they're gone well and we've got to start farming now extinction of or a next Inc shin vortexes a downward spiral of smaller and smaller population size. I mean, we've said before that small populations are very vulnerable to extinction, and they could get trapped in these cycles where basically because of their small population size, the population is having trouble surviving. And so it gets smaller and smaller and smaller and smaller populations are particularly vulnerable thio in breeding and genetic drift, which can actually lead to these extinctions. Vortexes. Now minimum viable population is the smallest population that can exist without facing extinction. So basically the smallest population that's not gonna get trapped in any of these situations, and you can see an example of it charted out here where, uh, This is a small and unstable population with a high chance of extinction, and these larger population sizes are going to be more stable now. Effective population size is the number of members of a population that will contribute two offspring of the next generation. And, uh, this is going to essentially be a way to determine the health and the survival ability of a population. You can also look at species area relationships. Do help determine biodiversity loss and extinction rates of populations based on what is called a species area perv. And basically, uh, this is a relationship that shows that, uh, the larger the area the species have available to them, the more species you will tend to see their with that. Let's go ahead and flip the page.