at this point people have been studying
the impacts that humans have had on the
world around us for a solid 50 years and
while it's hard to get a handle on
exactly how the choices we make every
day affect the environment there's no
question that our lifestyles our cars
our need for more farmland and our love
of all kinds of plastic stuff are
putting the hurt on ecosystems all over
the world human activity all by itself
just people doing what they do could be
responsible for the extinction of nearly
a thousand plant and animal species to
date most of them over the last century
and even if you don't particularly care
about the barbary lion or the saint
helena oliver the passenger pigeon or
anything else we've driven into
extinction the thing is
we need these other organisms the
ecosystems of the world are working very
hard for us every day filtering water
sucking carbon dioxide out of the air
producing all the food we eat all very
important ecosystem services
benefits that the natural world provides
us for free so having ecosystems and
keeping them intact is important not
only for the organisms who live in them
but also for us the animals who rely on
them for thousands and thousands of
things that we could never do for
ourselves over the next two episodes
we're going gonna look at these systems
and how our actions are affecting the
ecosystems that we need for our survival
basically we're messing up the
environment six ways from sunday but to
make it easy on ourselves let's start
with the top five
[Music]
you often hear about all the different
ways that our behavior is affecting the
biosphere extinctions climate change
deforestation acid rain desertification
pollution and more but you're asking oh
well why are all those things bad what's
going on how is this stuff turning the
earth into sausage i don't understand
well i do understand which is why i'm
qualified to make this video so let me
lay it on you the services that
ecosystems provide for us all the dirty
work they do can be broken up into four
different categories there are things
that we could never ever ever duplicate
or work around no matter what kind of
smartypants technology we come up with
first healthy ecosystems provide support
services that create and replenish the
foundation of the earth's biological
systems these services include recycling
all of the compounds that are necessary
for life through the carbon water
nitrogen and phosphorus cycles they also
include other processes we've talked
about before like forming new soils and
producing atmospheric oxygen some
ecosystems contribute more to these
services than others but none of them
can get these basic jobs done unless
they are intact two ecosystems also
perform provisioning services giving us
the raw materials we need to live like
the ocean provides food in the form of
fish sticks and stuff and rivers and
aquifers and other fresh water sources
give us water plants and animals also
yield all kinds of fiber that we use for
clothing and shelter and all around us
we find sources of fuel whether it's
biomass in the form of grasses or wood
hydropower in the form of flowing water
or the carbon locked in millions of
years old trees that we're now
re-releasing into the atmosphere but i'm
getting ahead of myself ecosystems also
perform super important regulating
services moderating many of the earth
systems that can get dangerous if they
get out of whack like as we learned in
biology fungi and other organisms take
on the task of decomposing dead things
in poop meanwhile plants help filter the
water you drink and the air you breathe
and provide flood control and they also
absorb all that carbon you exhale and
that your car belches out which in turn
helps regulate the climate and finally
number four ecosystems are just kind of
awesome it's nice to be surrounded by
happy plants and critters doing their
business nice robust ecosystems give us
places to play scenes to inspire us and
things to just discover and learn about
these are their less tangible but still
important cultural services an
interesting thing about ecosystem
services is that economists actually can
and do calculate the monetary value they
provide for humanity if for example we
had to do all of the things that
ecosystems do for us it would cost us 46
trillion dollars per year which is a lot
considering that the output of the
global economy is 66 trillion dollars
per year so yeah we should be happy that
we're not you don't have to pay for all
that but you'll notice that i keep
saying that ecosystems can only serve up
all this awesome sauce if they are
intact by that i mean they specifically
have to have their biodiversity intact
because ecosystems are just a bunch of
living and non-living things working
together so unless their living parts
are healthy they're basically just rocks
and weather the main reason biodiversity
is so important is that it makes
ecosystems more resilient to that
never-ending change we talked about a
few weeks ago ecosystems with high
biodiversity are way more resilient to
disturbances than those with low
biodiversity in a high biodiversity
system if you take one species out of
the mix it's less likely that the
ecosystem will collapse take a hectare
of amazonian rainforest in that little
patch of land there are more different
species of plants and animal than there
are in all of europe some of the species
of insect goes extinct there's less risk
that the whole house of cards will fall
than say in the sonoran desert where
there are very few organisms so the
disappearance of one species could
affect the entire ecosystem so the best
way to understand our impacts on the
environment is through how we affect
biodiversity unfortunately it turns out
that we've been doing a really bang-up
job of endangering some of the highest
biodiversity ecosystems on the planet in
some cases we're having impacts on the
organisms themselves directly in other
cases we're affecting biodiversity
indirectly by creating one or two
changes in that ecosystem that cascade
into all kinds of problems for living
things first let's look at that hectare
of amazonian rainforest again because
even though it's one of those super
resilient ecosystems we're having
serious impacts on it how
well first by removing a lot of what
makes a forest a forest trees according
to some estimates we are clear cutting
around 8 000 hectares of trees a day to
provide land to graze cattle on and to
harvest wood to make coffee tables or
whatever when you cut down a hectare of
rainforest suddenly a place where a few
thousand species used to live turns into
a place where just a handful of species
live some grass some weeds maybe some
rats or mice some insects and you know
some cows cause man we love cows and
when you take out so many of the living
things on that hectare of land a bunch
of things happen for starters you're not
just affecting that ecosystem but
neighboring ecosystems as well for
instance all those trees that were cut
down provided the service of regulating
the flow of all that rain that
rainforests get not only by absorbing
some of it but also by slowing down
runoff letting the water seep into the
soil before slowly making its way into
streams and rivers and ultimately the
ocean but when those trees are gone the
water hits the land and shoots off in
the nearest stream causing erosion and
washing minerals and chemicals all the
way to the sea where it affects marine
ecosystems and when i say effect i don't
mean in a good way this my friends is
what's called a cascade effect in this
case caused by deforestation one of the
most obvious observable human impacts in
addition to causing more flooding and
changes in water quality deforestation
on a large scale can lead to another
impact desertification or the spread of
dry unproductive landscapes but cutting
down trees doesn't automatically turn a
forest into a desert desertification is
driven along by additional factors like
overgrazing by cattle and over
irrigation so how can over watering
something make it turn into a desert
well when we use groundwater to irrigate
crops the natural salts and the
groundwater build up in the soil
eventually making it so salty that
nothing wants to live there over time
fertile land near desert ecosystems
become overtaxed and the desert spreads
and this is exactly what has happened in
china over the past century where
overgrazing and the city's unquenchable
thirst for water have caused the gobi
desert to grow by 3 600 square
kilometers
every year now these two impacts by
themselves clearly limit the
biodiversity of otherwise lush
ecosystems but because they also result
in fewer trees that provide the
all-important services of releasing
oxygen and absorbing co2 you know what
domino's going to fall next
the climate carbon dioxide the principal
greenhouse gas it insulates the earth so
it stands to reason the more co2 there
is in the atmosphere the warmer the
earth will be and the thing is we're
reducing the size of forests at the same
time as we're unleashing all kinds of
greenhouse gases by burning fossil fuels
this double whammy is much of what's
driving global warming as a result we're
seeing decreases in the levels of polar
sea ice which means less habitat for
polar bears seals and seabirds more
temperate animals are moving closer to
the poles and hotter drier conditions
are causing more grass fires and forest
fires and while the climate has changed
many times in the past those changes
usually took place over centuries or
even millennia giving organisms time to
adapt or move these changes are taking
place within our lifetimes and it's kind
of a huge deal and it's complicated it'd
take me at least like 10 minutes and 52
seconds to explain it all in detail
which is why i did that in another video
by now hopefully you can see how one
human impact can lead to another and how
even indirectly they can end up reducing
biodiversity but it's hard to overlook
the more immediate impacts we can have
on ecosystems one of the more in your
face ways we affect biodiversity is by
introducing non-native species either
intentionally or unintentionally again
there are so many examples of this that
you can learn more about it in another
video i did but suffice it to say
whether it's kudzu in north america or
cane toads in australia invasive species
have a knack for out-competing or
outright eating native species to the
point that it rocks the world of an
entire ecosystem and finally probably
the most direct impact we have on
biodiversity is simply over harvesting
certain organisms we're overfishing the
oceans to meet growing demand for
popular fish species like tuna while on
land we're exterminating important
predators like wolves to protect
livestock those cows again and the less
diverse those ecosystems are the more
vulnerable they become to disturbances
including those other four impacts i
just mentioned and the fact is there's a
bunch more where those came from because
there's a whole separate set of effects
that humanity has in the biosphere that
stems simply from us putting the wrong
amounts of certain stuff in the wrong
place at the wrong time that's what we
call pollution so tune in next time when
we'll explore what it really is where
exactly it's coming from and what we can
do about it thank you for watching
another kind of depressing episode of
crash course ecology and thanks to
everyone who helped us put it together
there's a table of contents over there
if you want to click to review anything
or the links are down below in the
description and if you have any
questions or comments or ideas for us
please leave them on facebook or twitter
or of course down in the comments below
you