Biodiversity | Biodiversity and human impacts | High school biology | Khan Academy

Today we're going to talk about biodiversity. So, biodiversity, as you might have guessed, comes from two words: biological and diversity. Essentially, it's the variations or the diversity present between living things.

Now, I grew up in the sunny state of Arizona, and at first glance, there doesn't seem to be much variety in such a hot and dry place. I mean, it's the desert, right? But if we take a closer look at a place such as the Sonoran Desert—here's a picture—we would find all kinds of different living things like saguaro cacti, jackrabbits, tarantulas, silver-haired bats, and the roadrunner, which is my personal favorite. So, we can say that the desert is actually quite biodiverse. In other words, it's home to a large variety of living things.

Since there are both big and small differences between different living things, we can think of biodiversity on three different levels. The first and smallest scale level is going to be genetic biodiversity, which is just the genetic variation within a group of organisms. A really great example of this kind of biodiversity is the rock pocket mouse. I know that's a mouthful of words to say, but it's really cute! I mean, look at this picture. This is a species that can actually be found right here in the Sonoran Desert, and the cool thing about this mouse species is that there exist both tan and black colored rock pocket mice.

So, even though both colored rodents come from the same species, their genetic biodiversity creates mice with completely different traits. What's even more awesome is the fact that these colors—tan and black—have come about due to natural selection. Scientists have found that there are more black colored rock pocket mice in places with dark black-ish lava rock, while there are more tan colored rock pocket mice in lighter colored sands. This makes sense because if you think about it, the mice are hunted from above by predators like birds. So, having a coat color that blends into their surroundings would increase their chances of survival.

Having this kind of genetic biodiversity is really great because the rock pocket mice can use many different colored landscapes as habitats. If, let's say, the landscape color were to change and suddenly become dominated by dark lava rock, then this population of mice would have the genetic diversity that it needs to adapt to this change.

The second level is species biodiversity, which is the variety of species in a particular area. Going back to the Sonoran Desert, there are all kinds of mammals, birds, plants, and insects. But what I think is even more mind-boggling is the sheer number of bat species there are. I mean, we have silver-haired bats, as I mentioned earlier, but also bats like spotted bats, western red bats, and even this kind of bat called Peter's ghost-faced bat, which I think is a really awesome name.

You're probably thinking, "Okay, Abby, this is really interesting, but so what?" Well, like genetic biodiversity, species biodiversity is super duper important because having a lot of different species means that more roles can be filled in an ecosystem, which makes the ecosystem healthier.

Moving on to the final level, we have ecosystem biodiversity, and this is just the variety of ecosystems on the planet. Now, we've been talking a lot about the Sonoran Desert, and a desert is actually a type of ecosystem on Earth. If you recall, ecosystems are made up of both living things and their physical environment. In this case, living things in the desert ecosystem could include things like rattlesnakes, scorpions, and cacti, while non-living things could include rock formations or sand dunes.

In addition to desert ecosystems, Earth has forest ecosystems, coral reef ecosystems, and all kinds of different ecosystems. Having all these different kinds of ecosystems is extremely critical for our survival because the diversity of ecosystems on Earth provides us humans with important resources and services. So, without ecosystem biodiversity, our quality of life—and in fact, our very survival—could be at risk.

As you can tell, every level of biodiversity is incredibly important for unique reasons. Now, biodiversity doesn't remain constant; we can think of biodiversity as something that can change over time. The important thing to remember is that speciation increases biodiversity, while extinction decreases biodiversity.

So, let's talk about speciation first. Speciation happens when one species evolves into two or more species over time. You might have heard or seen something that looks like this, and I'll draw it out right here to the right. This is just a very simple speciation model or a phylogenetic tree. We have here a common ancestor that branches off into different species over time. This arrow represents time or "t" for short. It's speciation events like these that have led to the biodiversity that we see on Earth today.

On the flip side, we have extinction, which causes biodiversity to decrease. What we mean by this word "extinction" is that a species or population of living things dies off completely. Notice that it can happen on different levels, too. For example, if a population goes extinct, then we no longer have the genetic variance in the gene pool, or the set of genes, for a particular species. But if a species went extinct entirely, then that species is no longer there to fulfill its unique role or its ecological niche.

You might have heard of the dodo bird, which is a species that actually went extinct way back in the 1600s. Some of the major causes behind the dodo bird's extinction include overhunting, habitat loss, and competition with some newly introduced species. Unfortunately, the last dodo bird was reportedly killed in 1681. Even though we can't enjoy the presence of dodo birds anymore, learning about this extinct bird actually brings up a really good question: What effect do humans have on biodiversity right now?

Well, it's sad to say, but humans are actually causing biodiversity to decrease. Things like climate change, habitat destruction, and over-exploiting resources have caused a huge loss of biodiversity. If you remember, having biodiversity is really critical to our survival, which is a big uh-oh. In fact, species extinction is now occurring at a rate 100 to 1,000 times faster than the background rate detected in fossil records. Because the extinction rate is much bigger than the speciation rate, the result is an overall loss or decrease in biodiversity.

So today we learned about biodiversity, which is the variety of life present on Earth. We talked about three different levels of biodiversity, moving from genetic biodiversity to species and then ecosystem biodiversity. We also talked about how biodiversity isn't stagnant or fixed in place; we have speciation events that can increase biodiversity and extinctions that decrease biodiversity. Finally, we learned that human actions are threatening biodiversity, as we currently have a greater extinction rate than the speciation rate.