hi it's mr. Andersen and welcome to
biology essentials video 46 this is on
communities this podcast and the next
podcast both deal with ecology ecology
is a fairly recent science if we break
down the word eco comes from the Greek
word IKOS which means house and so it's
the study of our house so it's the study
of life on our planet and how they
interact and when you're studying
ecology there are a few terms that you
want to kind of understand and so the
way I remember those is babenco so I
stutter on the B sohba bec po is going
to tell you all the different levels we
study within ecology so if we start at
the beginning with that be biosphere but
I like to start down here at the bottom
and so on BEC Bo if we start at O or the
organism level we just finished remember
talking about organ systems and so cells
make tissues tissues make organs organs
make organ systems and organ systems
makes organisms and so an organism would
be one individual like this bull elk
here in Montana if we have a group of
elk living together that's now a
population or all the elk in Yellowstone
Park would be a population if we have
not only the elk but the Wolves and the
willow and the Aspen and all of that
together now we're at the level of a
community or populations interacting if
we add the abiotic factors or the
nonliving factors now we're at the level
of an ecosystem so this would be a
picture of the Greater Yellowstone
Ecosystem it's not going to only include
the elk and the Wolves and the Bison but
it's going to include the temperature
and the pH of the water and um and the
amount of moisture that they get so
that's the ecosystem if we look broader
than that the next one would be biome
biome are going to be areas that have
similar climates so that's going to be
similar water and temperature over a
long period of time we've got a number
of biomes on our planet so I'm right
here in the northwestern coniferous not
quite in Canada but right there but
we're going to have deserts we're going
to have rainforests we're going to have
the taiga up here we're going to have
the polar area so these are all biomes
larger areas where they have similar
climate
and then finally we have the biosphere
and that's wherever life is on our
planet which is pretty much anywhere
there's water on our planet you're going
to find life there and so Bobek Poe
shows us that levels all the way from
biosphere down to organism but we are
dealing with community in this podcast
talking about how populations interact
and how populations change over time and
so if we lay it out basically
communities have structure it's based on
what species are found there and what's
the total diversity of species in that
area those species are going to interact
and one of the intimate interactions is
something called symbiosis example I'll
talk about is the leafcutter and on
communities are made up of populations
and populations change over time one of
the ways they change over time as they
grow all populations will undergo
exponential growth as they start to take
off but eventually they hit some
limiting factors some of those are based
on their density and some are not and
those are called density dependent and
independent limiting factors and so even
though all life starts at exponential
growth it will eventually reach logistic
or it'll bounce up and down for a long
period of time and then if we look at
growth population growth in humans the
study of that is called demographics and
so I'll end by talking about what we can
learn by studying human population
growth on our planet so let's start with
a community itself remember a community
is going to be made up of various
populations and so the first thing to
look at this is that picture I took here
just about a month ago before the snow
came and this would be up at highlight
reservoir and so if you look here we
mostly have pine trees you can see um
but if I were to count all of the
different pine trees that we have so
we've got a lodgepole pine and we've got
a Engelmann spruce or whatever if I were
to go through and in a large area count
all the different types that we have and
how many are there are of each and put
those in a pie chart
that'd be species composition another
thing in a community then is the total
diversity not only you know what's the
largest amount of that we have here but
what's the total amount that we have and
so this would be all the fungi they were
able to collect in an area and so that
shows us species diversity or
biodiversity in an area and if I were to
pose the following question you know on
our planet so
this is our planet right here and the
Equator is here where are we going to
have the greatest species diversity on
our planet you might think well right
here on the equator it's going to be the
most amount of light but we'd actually
find not if we were to graph it so if we
were to go from the equator and we were
to go to the poles and we are going to
look at just diversity we'd find that at
the equator it's kind of stagnant
there's not a lot of movement of the
weather and so we're going to have low
species diversity they'll actually peak
out where we have those rainforests and
then it'll eventually drop off obviously
into the poles so there's going to be
less species diversity there um but
that's community structure what's there
and how much total is there now there's
also going to be interactions between
the populations there and we call that
symbiosis symbiosis scientists say it's
it's living together and so they kind of
break it into three different ways that
you can live with other organisms you
can live mutualistic aliy where you both
help you can live parasitically or
you're damaging one or you can live
commensalism and so basically that's
somewhere in between where you're not
harming them
I kind of think you're either helping or
or harming if we look at these
relationships but let's go to a really
cool one this is symbiosis and
leafcutter ants leafcutter ants I'm sure
you've seen the video they cut a leaf
off and then they'll carry it back
underground into their Mound basically
what they do is they feed it to a fungus
so there's a fungus within that leaf
cutter ant colony this is the queen ant
the just giant compared to the other
ants but basically what they're doing is
they're chewing up the leaf and they're
feeding it to the fungus the fungus then
breaks down the cellulose inside there
and produces this sugar that the plant
that the that the ants can then eat and
so that's a symbiotic relationship now
between the ant and the fungus the
fungus gets a constant supply of food a
place to live and then the it's going to
provide food for those ants and when
they form a new colony they'll carry the
fungus with them so they're really
farming that fungus now it even goes
deeper than that
so when scientists were looking at this
farming of the fungus they found that
those the fungi are never infected so
there's never an infection in their farm
like we have in our farms and what they
found is that when you
look at the ant itself there's actually
bacteria living on the ants especially
high in the ants that are working in
this farm and so those are similar to
some of the fungi and some of the
bacteria that we use to make our
penicillin or to make our antibiotics
excuse me and so now we've got a
mutualistic relationship between this
bacteria that's living on the ant and
the ant itself and so it's evolving it
also has this symbiosis with the fungus
and so it just keeps going and going and
going and going and so these are all
symbiosis or these interactions between
populations some are good but obviously
if I'm a tree living right next to this
maybe it's bad for me as a tree okay so
let's go to growth then so within a
community we have populations and
populations going to change over time
as they start to grow all populations
will undergo exponential growth in other
words even though elephants might have a
station of almost two years if you have
elephants in an area that one elephant
is quickly going to become two elephants
which is quickly going to become four
and then you get this pad characteristic
exponential growth pattern so if you
were this is just a mathematical model
of exponential growth this is actually
human growth and so here's humans from
10,000 BC until the year 2000 where the
population hit six billion you know
we're going right at about seven billion
right now and so if you look at this
this would be exponential growth in
other words it's just taken off on
especially since the Industrial
Revolution but you could imagine that it
can't do that forever
so our population is eventually going to
hit some limiting factors we're going to
run out of food we're going to run out
of space disease is going to take over
and so we call these things limiting
factors and they come in two different
types density dependent density
dependent are based on the size of the
population so an example would be you
know a lack of food would be a density
dependent limiting factor if there's no
food if there's no space if we have
disease takeover because we're living in
close proximity to each other then those
are all density dependent limiting
factors so that's going to limit the
growth density independent are going to
be those that aren't related to
population size so what are they related
to they're related to chance and so a
giant volcanic eruption it's just chance
is still going to limit growth but it
would be density independent or a
tsunami killing you know thousands and
thousands of people would be an example
of a density independent limiting factor
and both of these are going to act on
that exponential growth and they're
eventually going to level it off and so
eventually all populations will undergo
what's called logistic growth and and
it'll approach something that we call up
here a carrying capacity in other words
in it's the area in an area excuse me
it's the maximum number of individuals
that an Arri area can support and so our
planet has a carrying capacity and so
population human population growth won't
go on forever because we're eventually
going to run out of supplies food and
space would be one example and so
logistic growth is that leveling off and
there are some populations that will
quickly go exponential and then they'll
just die off and then they'll go
exponential again so like a boom and
bust cycle but generally if you're
humans if you're like humans where you
takes a long time to reproduce and you
don't have a lot of offspring then
you'll eventually approach what's called
logistic growth and so this is from the
UN projection so this is right here
we're in 2011 our population is right
around 7 billion on the planet and so
this is what the UN predicts that this
would be the high end so this would be
the maximum our population could get to
by the year 2100 and this would be the
low end but the neat thing about this
chart is they break it down by different
continent so here would be an Asia here
would be Africa so this would be the
high end low end so they've got a high
end in Asia of saying by the year 2100
which I probably won't be around then
but they're saying that an high end you
could have in Asia you could have almost
eight billion people living there and so
what's the world population going to do
it's eventually going to approach what's
called logistic growth but it depends on
where you are so in the United States if
we didn't count immigration we would
actually be at logistic growth we're
actually leveling off in the u.s. right
now
and so that graph doesn't tell us
everything if you really want to know
the answer you have to look at what's
called an age structure diagram an age
structure diagram to kind of lay this
out for you
what we have our guys on one side girls
on the other so this is in Angola and
we'll compare that to the u.s. in just a
second and so this is the number of
individuals in this study who are from
zero to five and the number who are from
five to nine and so we sometimes call
this an age structure we sometimes call
it a population pyramid because you get
this pyramid shape and so if you ever
have a pyramid shaped like this where we
have you know most of our population is
really really young this is a population
that's going to go exponential so it's
going to take off because we have all of
these young kids they're going to
produce young kids and so it's going to
be exponential growth um if you look at
the United States it's not going to look
like that so if you look at the United
States it looks quite a bit different
and so we have a lot of people that are
older but we also have this bubble right
here in the middle those would be the
baby boomers if you know anything about
the history in the United States and
then it's kind of dropped off here at
the bottom and so as it drops off at the
bottom that means since it's pretty flat
going across this is a population that's
going to go logistic so it's approaching
logistic and sometimes you'll see age
structure diagrams that are actually
they go in quite a bit at the bottom and
those are going to be ones that not only
have they leveled off at some kind of a
carrying capacity but they're actually
dropping off Italy is an example of a
country I know that's dropped off quite
a bit and then if we look at China for
example where we're seeing it we saw a
huge amount of growth there's some
interesting things here this would be
the typical population pyramid at the
top so they were undergoing exponential
growth but then they realized that and
they had this one child policy and so
there was this decrease and so they're
going to level off and India is actually
going to take off and be the most
populous country on
planet and so are humans going to hit
all these density-dependent limiting
factors probably not because we were
able to figure out new ways to get
resources new ways to get energy but
eventually I'm not pessimistic I think
humans were are eventually going to kind
of reach a logistic kind of a pattern
and we're going to kind of stabilize I
don't know ten billion something like
that that's my guess but again I'm not
going to be around so it's no big deal
so that's communities community or
interactions and I hope that's helpful