Human activities that threaten biodiversity (video) | Khan Academy (2024)

Video transcript

(gentle music) - [Narrator] Why isbiodiversity threatened? We're gonna talk aboutsomething that we'll call local factors, as opposed to more global human effects, but before we go into some of those, we really needto talk about the fact that the human population is growing fast. In 2014, the estimate wasjust over seven billion people on earth. Human population growth is exponential. The more people you have,the more reproduction you have going on. If you have more reproduction happening, then the curve on a graph of population versus time is gonna getsteeper and steeper and steeper to the point where we'relooking at about nine billion people by the year 2050. It was Thomas Malthus in 1798 who came up with the concept of carrying capacity. Basically, he said that the earth can't indefinitely support anever-increasing human population. That's a concept that,to us I think, seems quite clear, but Malthus was a member of a social force at that time, basically, the clergy that felt the earth was put here for humans to use and upon which we should go forth and multiply. But Malthus was amongthe first in recognizing that there was no waythat human population could increase indefinitely without having some sort of an effect on the environment and the environment'sability to support us. The logic he used led him to the fact that based on the kind of farming he saw around him at the time, there would soon be so many people, therewouldn't be enough to eat. Basically, the planet was gonna check population growth through famine. He had seen famine. He knew what it was like, so the planet was gonna takecare of it if we didn't. In other words, we wouldexceed the planet's carrying capacity for human beings. The question arose, what actually is the carrying capacity ofplanet earth for humans? The answers, like mostscientific replies, it depends. We haven't hit the Malthusian limit yet because of a very important thing, and that's human technology, the ability to come up with answers to problems that are facingus at almost every turn. In this case, the answerscame through science and technology thatincreased food production. This made it possible for us to get back on the exponential population growth curve and escape Malthus' view ofwhat the upper limits were. In fact, there are someestimates that suggest if we all did with lessand lived at the lowest possible level for existence, earth could support an estimated 40 billion people. But even if we were able toreach a carrying capacity of 40 billion, it would require sacrifices for all humans on earth,some more than others. It raises a huge questionabout the quality of life, which points out what'sincreasingly becoming the single most important fact about human population growth on earthtoday, that the world's wealthiest 16% of the people on earth use 80% of the available resources. The bottom line here, as Isay, is that it's complicated. We recognize that the humanpopulation is growing. We recognize that resourceutilization is much higher in some countries than in others. But what I really wantto do is circle back to our primary objective and examine what this really means for biodiversity. If you asked anyone,they'd say it's pretty clear that human populationgrowth and resource utilization have huge effects not just on our social and economic well being, but, of course, on biodiversity. But how, exactly? It translates into decreasesin species richness. It's primarily through theloss of species richness that our greatestpopulation growth effects are gonna show up. If we simplify it, it's as fundamental as no two things can occupy the same place at the same time. That's what we're talkin' about. If a human is living in a given place, fewer native plants andanimals can live there. The details of how human population growth actually affect speciesrichness are only now starting to be worked out. We don't have a lotta data yet. It's a huge, complex problem. One of the pioneering papers on this was published in 2003by McKee and colleagues. They measured a number of factors in 114 different countries,and what they discovered was that, out of all the factors that they looked at, human populationgrowth and species richness were tightly linked. In other words, if you wereto slow population growth, that might be sufficient to stop drops in species richness. They suggested that all you need to know is population size. Plug this into the equation, and you can figure out in a given place what effect it's going to have on biodiversity. Calculations show thatthe number of threatened species in an average nation is going to increase 7% by 2020 and 14% by 2050 just based on population growth alone. That's a very simple relationship, but if you open up that box represented by the idea of population growth and unpack what it means, you're talking about lots of human-induceddrops in biodiversity. And, as usual, things get complicated. I'd say that there are seven major human mediated causesof biodiversity loss. They can be grouped intotwo main categories, localized ones and global ones. The global causes we'lllook at in separate videos, but for the localized ones,we're gonna list four: land-use change, pollution,resource exploitation and introduction of exotic species. Of course, they overlap a little, but I think, for the most part, these are good ways of unpackingour box of problems. Let's start with land-use changes. These include thingslike habitat destruction and conversion of natural habitat to human use that isn'tnecessarily compatible with the organisms that are native there. This includes cropmonoculture that results in a very dramatic dropin species richness in a given habitat. When people think abouthabitat destruction and conversion, they think ofslash-and-burn agriculture, destroying rainforests, plowing over stuff or removing the tops of mountains to get at resources like coal. But there are ocean-use changes too that I think we should not ignore. Think of coastal wetland lossand mangrove destruction. Urbanization is an enormouschange in land use. More people need more homesand more places to work. That, in turn, requires an expansion of agricultural resources and the spread of those into environmentsthat were previously untouched. It's a very complex problem, as I say, but, simply put, the more people you have, the less natural undeveloped habitat there's going to be. And it's very easy tosee how that's linked to a drop in biodiversity. The second local factor is pollution. A lot had been done to bring the subject to people's attention to the point where we think about it as enormous disasters attached to superfundcleanup sites and such, but there are other, more subtle ways of polluting the environment that I think are worth thinking about when we talk about drops in biodiversity. For example, the degradationof local habitats through human activitiesthat cause downstream effects, things likethe leaching of harmful chemicals from mines into the water table. Waterborne pollutants can pop out in very unusual places and havereally big downstream effects, if you'll excuse thepun, on the reproductive viability of organisms thathappen to be in those places. There are also dead zones in the ocean caused by nitrogen fertilizersthat wash into rivers. Where the rivers flow into the sea, the nitrogen causes blooms of bacteria, which in turn, use up the oxygen. Anything that tries to be active in an area where the oxygen is being used up by the bacteria,any oxygen-requiring organism, that is pretty much any animal, for example, is going to havea really hard time of it. These dead zones are now starting to be a little bit betterunderstood, and it's pretty clear that they're growingin size and in number in relation to population growth. Then there's the overallproblem of waste disposal. Untreated sewage is a classicproblem for biodiversity. It's not just, of course, human waste. It has to do withsometimes bizarre chemistry involved in the high-techstuff that we're making now. We're talking about chemical compounds, including drugs and PCBs. There are lots of strange molecules that humans are producing and dumping. In some cases, you getthese hormone mimics, simple compounds derivedfrom prescription drugs and other man-made chemicals that get flushed into waterways. Hormone mimics act likenaturally occurring hormones that control normal development of wild organisms,particularly water-living ones. Hormone mimics can also adversely affect their reproductive organs,and there are many, many, many examples ofthis kind of pollution, one that people wouldn'tnecessarily think of. Another one that doesn'timmediately occur to people is noise pollution. Birds in cities arereacting to noise levels, so even the organisms that are not being wiped out because of our expanding cities are starting to adaptto an urban environment by changing their behaviorand reproductive patterns. And some of them just can't do it. Noise can also be a major factor in marine mammal survival. Evidence suggests that sonor pollution interferes with thehealth of marine mammals. Patterns of reproduction can also be upset by our introduction of light pollution to places where there wasn't light before. Sea turtle hatchlings can be impacted by artificial light heading toward it instead of the ocean when they hatch out of their nests on the beach. And bird strikes on buildings are greatly increased at night whenthe lights are left on. Let's look at the third local factor, resource exploitation. This gets to the simple idea that humans are always using thingsfrom their environment. We are inextricably linkedto that environment, and we use up stuff, we always have. We have to do that in order to stay alive. Their are classic ways we use resources like hunting, cuttingdown forests for firewood and lumber, where doesthe biodiversity go then? A big one for me as a marine scientist, of course, is fishing. We talk about the harvest of fish, but it's not really agathering of what one sows, it's really a straight-upremoval of a resource, as much as mining is. There are attempts to control overfishing, but to a large extent, we often don't have enough data to knowjust what a sustainable amount of extractionis until it's too late. Before we were movedto action, for example, the cod fishery had collapsed on the Grand Banks of Newfoundland. Today, we have no ideawhat the long-term effect of huge trawls scrapingover the sea bottom will be. Now countries are pushing to fish more on the Antarctic, which is a problem, because fish, like most things there, grow slowly in the cold Antarctic depths. The last local causeof reduction in species richness I wanna mentionis the introduction of exotic species, andwe'll talk about those in the next video. So just to bring it allback to this concept of carrying capacity, the emerging message is that if everyone on earth can manage to do more with less, especially in places where we presently use uprelatively so much more, we might be on tracktowards a more manageable carrying capacity for humans on earth with a decent quality of life. In our world of finiteresources, it's a balancing act between humans and everyother species on earth. We have to learn to do more with less to keep that natural balance, the natural species richness. The biodiversity that keeps ecosystems, and therefore all of nature,including ourselves, healthy. (gentle music)