Human impacts on ecosystems | Biodiversity and human impacts | High school biology | Khan Academy

What we're going to talk about in this video is how human activity creates changes in the environment. Not just any changes, but changes that can disrupt an ecosystem and can threaten the very existence of some species.

For the sake of this video, we'll think about it in five different dimensions. The first is habitat destruction. So this over here is a picture of some trees that have clearly been cut down. There are many reasons why trees could be cut down like this. One could be maybe there's some logging, and we human beings do need wood. Maybe it's being cleared for agriculture, which we also need. But when you do that, it's clearly eliminating the trees. Many animals, many different types of species, were probably living in or amongst or on those trees. If you do too much of that, they might not have anywhere to live or they might not have enough places to live to really thrive.

Now, another form of anthropogenic changes, or changes induced by human activity, would be pollution. This right over here, you can see the exhaust, so to speak, from a coal-fired power plant, and that is polluting the air. Harmful chemicals are being released, including greenhouse gases. That's going to have other effects above and beyond just making the air less pleasant. But pollution isn't just about harmful chemicals going into the air. It could be about harmful chemicals going into the water. It could be runoff from irrigation or some other type of chemical. You can even have noise pollution. You might think of that as an annoyance, but it can actually disrupt how certain animals behave. In fact, it could raise the stress level, which can change the biology of animals in subtle but important ways.

Another dimension in which we humans are affecting ecosystems is by introducing species to places where they might not have been before, especially what's often called invasive species. So this is a picture here of nutria, oftentimes referred to as nutria rats. I was born and raised in Louisiana, and there are many nutria in Louisiana. They did not come from Louisiana; they came originally from South America. They were brought to the Gulf Coast, to the southern United States, for their furs. The demand for their furs did not keep up, and these nutria escaped. Now they are everywhere. You might just once again view that as an annoyance, but they start overpowering other species. They are competing with other animals for the same food, for the same niche in the ecosystem. Nutria are also infamous for eating the plants that hold together the soil and the wetlands. The more that they do that, the more that soil gets eroded. Then you have issues like habitat destruction; you have fewer wetlands for other species.

Now, another dimension is over-exploitation. So this is a picture here of what's known as trawling. You take a big boat, and you have this huge net. The boat goes while the net is just grabbing all the fish in the water. These dots here are all fish, and actually it extends out here because the net is bulging outward like that. You can see it's a very efficient method of getting fish, but you could over-fish. If you take too many fish out of the ocean, you're not going to have enough to reproduce and keep the population going. Even though you might get a lot of cheap fish very efficiently in the short term, in the long term, the fish might go away.

All of these, as you can imagine, connect in many ways. A fifth dimension we could talk about, although it's very related to pollution and even deforestation, is climate change. The climate change that we are most familiar with right now is this notion of global warming, which is occurring as we have rising levels of greenhouse gases like CO2. Those could be released from things like this coal-fired power plant that we saw a few minutes ago. But there are many other sources of things like CO2 and other greenhouse gases. As we human beings release more and more of this into the atmosphere, these greenhouse gases trap more and more heat. That, over the long term, increases average global temperatures.

That doesn't just affect temperature; when you affect temperature, it can affect rainfall, it can affect wind patterns. As we see in this picture over here, it can affect things like the amount of sea ice we have. Because if, on average, global temperatures are increasing, then water temperatures could be increasing, and you have more melting sea ice in both the Arctic and Antarctic. For example, in the Arctic, where you have polar bears, they would have less ice to be on when they're hunting the walruses or the seals, or frankly just ice to be on to rest from swimming in the water. That melting ice also can contribute to rising sea levels. It's not just the melting ice that's contributing to rising sea levels; it's also that water has different density at different temperatures.

As you have rising sea levels, that affects ecosystems around the planet, especially ecosystems close to the water. One of the species that is most impacted by that is human beings. Most human beings actually live very close to sea level, near a body of water. As those sea levels rise, they will have a very profound impact on a lot of animals, but especially human beings.