(gentle music) - [Narrator] Why is
biodiversity threatened? We're gonna talk about
something that we'll 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 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 get
steeper and steeper and steeper to the point where we're
looking 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 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 environment's
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 gonna check population growth through famine. He had seen famine. He knew what it was like, so the planet was gonna take
care of it if we didn't. In other words, we would
exceed the planet's carrying capacity for human beings. The question arose, what actually is the carrying capacity of
planet earth for humans? The answers, 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 turn. 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' 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 40 billion people. But even if we were able to
reach a carrying capacity of 40 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% 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 have huge effects not just on 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 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 and
animals can live there. The details of how human population growth actually affect species
richness 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 2003
by 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 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 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-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 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 unpacking
our box of problems. Let's start with land-use changes. These include things
like habitat destruction and conversion of natural habitat 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, 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 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 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 to
see 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 superfund
cleanup 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 degradation
of local habitats through human activities
that cause downstream effects, 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-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 in 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 in 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 sonor pollution interferes with the
health 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 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. Their 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 talk about the harvest of fish, but it's not really a
gathering of what one sows, 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 wanna 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. (gentle music)