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why is biodiversity threatened we're going to talk about something that will call local factors as opposed to more global human effects but before we go into some of those we really need to talk about the fact that the human population is growing fast in 2014 the estimate was just over 7 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 going to get steeper and steeper and steeper to the point where we're looking at about 9 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 an ever 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 among the first in recognizing that there was no way that human population could increase indefinitely without having some sort of an effect on the environment and the environments ability 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 there wouldn't be enough to eat basically the planet was going to check population grow through famine he had seen famine he knew what it was like so the planet was going to take care of it if we didn't in other words we would exceed the planets carrying capacity for human beings the question arose what actually is the carrying capacity of planet Earth for humans the answer is like most scientific 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 facing us at almost every term in this case the answers came through science and technology that increased food production this made it possible for us to get back on the exponential population growth curve and escape malthus's view of what the upper limits were in fact there are some estimates that suggest if we all did with less and lived at the lowest possible level for existence earth could support an estimated forty billion people but even if we were able to reach a carrying capacity of forty billion it would require sacrifices for all humans on earth some more than others it raises a huge question about the quality of life which points out what's increasingly becoming the single most important fact about human population growth on earth today that the world's wealthiest 16% of the people on earth use 80 percent of the available resources the bottom line here as I say is that it's complicated we recognize that the human population is growing we recognize that resource utilization is much higher in some countries than in others but what I really want to 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 population growth and resource utilization of huge affects not just in our social and economic well-being but of course on biodiversity but how exactly it translates into decreases in species richness it's primarily through the loss of species richness that our greatest population growth effects are going to 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 talking about if a human is living in a given place fewer native plants and animals can live there the details of how human population growth actually affects species richness are only now starting to be worked out we don't have a lot of data yet it's a huge Lexx problem one of the pioneering papers on this was published in 2003 by McKee and colleagues they measured a number of factors in a hundred fourteen different countries and what they discovered was that out of all the factors that they looked at human population growth and species richness were tightly linked in other words if you were to 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 that the number of threatened species in an average nation is going to increase seven percent by 2020 and fourteen percent 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-induced drops in biodiversity and as usual things get complicated I'd say that there are seven major human mediated causes of biodiversity loss they can be grouped into two main categories localized ones and global ones the global causes we'll look at in separate videos but for the localized ones we're going to list for 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 unpacking our box of problems let's start with land-use changes these include things like habitat destruction and conversion of natural habitats to human use that isn't necessarily compatible with the organisms that are native there this includes crop monoculture that results in a very dramatic drop in species richness in a given habitat when people think about habitat destruction and conversion they think of slash-and-burn agriculture destroying rainforests overstuff or removing the tops of mountains to get at resources like coal but there are ocean use changes to that I think we should not ignore think of coastal wetland loss and mangrove destruction urbanization is an enormous change in land use more people need more homes and more places to work that in turn requires an expansion of agricultural resources and the spread of those into environments that were previously untouched it's a very complex problem as they say but simply put the more people you have the less natural undeveloped habitat there's going to be and it's very easy to see how that's linked to a drop in biodiversity the second local factor is pollution a lot have been done to bring the subject to people's attention to the point where we think about it as enormous disasters attached to Superfund cleanup sites and such but there are other more subtle ways of polluting the environment which I think are worth thinking about when we talk about drops and biodiversity for example the degradation of local habitats through human activities that caused downstream affects things like the leaching of harmful chemicals from mines into the water table waterborne pollutants can pop out in very unusual places and have really big downstream effects if you'll excuse the pun on the reproductive viability of organisms that happen to be in those places there are also dead zones in the ocean caused by nitrogen fertilizers that 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 and requiring organism that is pretty much any animal for example is going to have a really hard time of it these dead zones are now starting to be a little bit better understood and it's pretty clear that they're growing in size and a number in relation to population growth then there's the overall problem of waste disposal untreated sewage is a classic problem for biodiversity it's not just of course human waste it has to do with sometimes bizarre chemistry involved in the high-tech stuff 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 get these hormone mimics simple compounds derived from prescription drugs and other man-made chemicals that get flushed into waterways hormone mimics act like naturally 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 of this kind of pollution one that people wouldn't necessarily think of another one that doesn't immediately occur to people is noise pollution Birds and cities are reacting to noise levels so even the organisms that are not being wiped out because of our expanding cities are starting to adapt to an urban environment by changing their behavior and 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 sonar pollution interferes with the health of marine mammals patterns of reproduction can also be upset by your 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 when the 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 things from their environment we are inextricably linked to that environment and we use up stuff we always have we have to do that in order to stay alive there are classic ways we use resources like hunting cutting down forests for firewood and lumber where does the biodiversity go then a big one for me as a marine scientist of course is fishing we talked about the harvest of fish but it's not really a gathering of what one sews it's really a straight-up removal 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 know just what a sustainable amount of extraction is until it's too late before we were moved to action for example the cod fishery had collapsed on the grand banks of Newfoundland today we have no idea what the long-term effect of huge trawls scraping over 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 cause of reduction in species richness I want to mention is the introduction of exotic species and we'll talk about those in the next video so just to bring it all back 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 up relatively so much more we might be on track towards a more manageable carrying capacity for humans on earth with a decent quality of life in our world of finite resources it's a balancing act between humans and every other 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 you