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