- [Lecturer] So in this last lecture,
ultimately we look at the highest levels
of organization on this planet,
which is community
interactions and ecosystems,
now let me recap again what the difference
between communities and ecosystems are.
Community is all living things in an area,
so when we look at an area
in which these organisms are residing,
we look not only at one organism
but all of the interactions
of all of the organisms
within that environment,
and some of the dynamics
that occur as a result.
There are about five different
types of interactions
that can affect the
evolution of these species
as well as the dynamics
of how the ecosystem thrives and survives.
And then ecosystems
not only looks at life,
but also non-living aspects
such as energy flow,
water recycling, nutrient
cycling and things of that sort.
And so the latter half of this
we'll look at the actual
ecological pyramid,
we'll look at the hierarchy of life
as well as the dynamics
of how energy flows
through an ecosystem
and how nutrients are
recycled within an ecosystem
through the various living organisms.
So those will be the last two concepts.
Your questions on your quiz
are pretty much split down the middle
so half of them are gonna
be on community interactions
and the other half on ecosystem
relationships and dynamics.
All right, so one of the
things you're gonna see too,
as we start talking about
the community interactions
is that evolution of some species
is completely dependent upon
some of these interactions,
the things that have evolved
within a species comes about
because of their interactions
with other organisms
within the same region.
Now there are six here,
but there's really only five
because I consider herbivory
and predation one and the same,
it just matters what you eat, and in fact,
when we look at the
relationship of how that affects
the population, it's
overall growth and such,
it's the exact same relationship.
So on your quiz you're not gonna see
a difference between
herbivory and predation,
because all herbivores are are just,
they eat the plants and
other types of organisms,
whereas predators eat other
animals and things of that sort.
So, but the relationship
that we're gonna study
is pretty much the same,
so it's gonna be seen as predation.
Now, these pluses and minuses,
from what we learned before spring break,
we were talking about what dynamics
affect the population's growth rate,
and that's really what these
pluses and minuses mean.
A minus means it negatively affects
the population growth rate,
a plus means it positively affects
the population growth rate,
meaning it increases and sustains
the population in its growth.
So the negative obviously decreases
the population's ability to grow,
it limits its growth rate
as well as the number of organisms.
And I've got several videos to show
many of the dynamics of these
that will be represented by quiz questions
you'll have regarding them.
So let's start with competition.
This is the only interaction
between living organisms
that is not beneficial in any way,
in fact, this leads to
a particular principle
that we study in ecosystems
called the competitive
exclusion principle.
So two species competing over a resource
ultimately hurts both species.
One or two things have to
happen in the competition,
either one species wins,
and when we talk about
winning, we mean surviving
and the other species essentially dies off
because it cannot out-compete
the other species, okay,
so that's one way.
There's another way
though, they can coevolve
in which case they each start using
a different aspect of
that ecological niche,
which is the resources that they need,
the space, the food and whatnot,
and by this coevolution,
because they change
their ecological niche,
and I'll give you some examples of this,
then both species survive.
And we see both of these things,
we see out-competition where one survives
and the other dies off,
or we see coevolution of these species
where individuals within the
population essentially adapt
to a different ecological
niche within that environment
and the competition stops.
But this is what we call
the competitive exclusion principle,
which is that no two species
can indefinitely occupy
the same ecological niche,
one or the other of
those things will happen.
Now let me show you some examples.
If very closely-related species of bird
tend to inhabit the same tree,
in some situations they
might compete over the space,
however, through coevolution,
some birds may prefer the top branches
where they might undergo
their nesting and feeding
and things of that sort, and reproduction,
and others might favor
more lower branches,
and this type of coevolution
allows them to both
use the ecological resource
in a different way,
and so the competition stops
and both species end up surviving.
Now that's not always the case,
in some cases you just out-compete
other species completely
and eradicate them from that
environment, and you win out.
Okay, so that's competition,
neither species benefits from it,
but it does lead to
coevolution in some cases,
however, it leads to
whichever one is best fit
and can out-compete the
other of the species,
but it harms both in the process.
Now the next three are
what we call symbiosis.
Now most of the time when
people think of symbiosis
or symbiotic relationships,
they think of the first one, mutualism,
but there are actually two others,
commensalism and parasitism.
And so symbiosis is not
synonymous with mutualism,
mutualism is one type of symbiosis,
commensalism is another type of symbiosis
and parasitism is actually
a form of symbiosis.
So what does symbiosis actually mean?
It essentially is one organism
benefits from another organism,
but does the other
organism benefit in return?
Well, in these three
types of interactions,
one of them is mutually beneficial
which is why we call it mutualism,
in which both species
benefit from the partnership,
and I'm gonna show you a video
that illustrates this in a second.
But we've talked about
a number of these types
of mutualistic relationships,
like a lichen, or the fungi and the algae
both help each other,
that's a perfect example of
a mutualistic relationship.
We have many examples of
mutualism in our bodies as well,
one of which there are microorganisms,
bacteria within our intestines
that actually take of the
feces that we cannot break down
and they break it down into
essential vitamins and nutrients,
so without those microorganisms
in our intestines,
we really can't get all of the
vitamins that we always need.
That's one of the reasons
why, when we take antibiotics,
usually people suggest to take probiotics,
which are, you know, yogurts
and other types of things
that have this good bacteria and such,
because we are not only
killing off the bad bacteria
that are causing the disease
but we're also affecting the good bacteria
that we have this mutualistic
relationship with.
Now here's one of the
things about mutualism.
It not only creates a partnership
that benefits both individuals,
but it also creates what
we call an interdependency,
meaning if one of the two organisms
that are in this mutualistic
relationship die off,
or, you know, because of some
other type of relationship,
predation or competition
or something like that,
ultimately the other
one is harmed as well.
It's not just one goes away and says,
oh well, I'm still fine,
no, the relationship when it leaves
also hurts the other one as
a result, think about it.
If the lichens don't, if the
fungi don't have the algae,
they can't get the
nutrients that they need,
and if the algae don't have the fungi,
they can't get the
protection that they need,
and they both are harmed as
a result of one being lost.
If we don't have those
bacteria in our intestines,
then we don't get a lot of
the vitamins that we need
as a result of it and so on and so forth,
so you can see how this interdependency,
it's beneficial when both are
there but when one is lost,
it hurts the other as a result of that.
Now, commensalism,
most people have not
heard of commensalism.
Commensalism is where one benefits
but neither hurts nor helps the other.
So in this scenario, if the
organism that was symbiotic
were to all of a sudden go away,
it wouldn't hurt the other individual,
let me give you some examples.
Moss, moss is a type of plant
that can actually use a tree
as it's kind of anchor to
be able to support itself,
the moss benefit from this relationship
but the tree doesn't,
the tree is not hurt, because
the moss isn't parasitic,
nor is the tree helped because
the moss, unlike fungi,
doesn't really give
anything back to the tree,
so this is an example of commensalism.
Another example, barnacles on a whale,
the barnacles essentially
attach to the whale
and they get a free ride,
as the whale travels through the oceans
they essentially are filter feeders
and they're able to get the
nutrients that they need,
now, they're not parasitic,
they don't suck the blood from the whale,
nor do they give anything
back to the whale,
so that's another example of commensalism.
A third example of commensalism is us,
we have these little mites
that live in our hair
follicles in our skin,
and they don't give anything back to us,
they just get a free ride in our skin,
make you crawl a little bit,
but ultimately these mites
in our hair follicles,
this is an example of commensalism.
If they would all of a sudden go away,
we would be neither
helped nor hurt from that
and so that's why it's a
plus zero relationship, okay?
Now the last one is parasitism.
Now a lot of times people
wouldn't think parasites
are actually a form of
symbiosis but they are,
because again, this is where one organism
is benefiting from the other.
Now in this relationship, it is harmful,
but, as we've mentioned,
parasites also evolve to a point
where they don't outright kill the host,
a good parasite is one
that can live in the host
and not kill it,
however, it does weaken the host,
which is why it has a
negative relationship,
the parasite can spread
disease, can weaken the host,
can rob the host of nutrients
and things of that sort,
but it's still considered symbiosis,
it's still a form of symbiosis
because of the definition of symbiosis.
So mutualism, commensalism and parasitism,
these are three examples of
symbiosis that I'll test you on.
Now the last one is an
obvious one, predation,
and again, I said herbivory
is tied in with predation
because ultimately this is a relationship
where one organism outright
kills the other organism,
so whether it's an animal
eating another animal
or an animal consuming a
photosynthetic organism,
these are all, you know, very
well understood relationships
where the predator always benefits
and the prey is hurt in that process.
Now all of these types of interactions
are actually key for the
stability of an ecosystem,
except one, competition,
competition is the only one
that brings no stability to an ecosystem.
Mutualism, commensalism,
parasitism and predation,
these are all ways in which
the dynamics of interactions
in which species have in an environment
help to support that,
even predation has its
key role in making sure
that there is proper balance
within the ecosystem.
Now, that brings us to our last concept,
this part, keystone species.
A keystone species is essentially
any organism in an environment
that makes up a small
proportion of the community,
yet the disappearance of this species
can have drastic influence
or dramatic collapse of the ecosystem.
So a keystone species is not a species
that forms the bulk of any
species in an environment,
in fact, in some cases
they might just be a very,
very, very small portion,
however, they, like a
keystone in a building,
though small, provide
stability for that ecosystem.
Now there's not always
just one keystone species,
there can actually be
several keystone species.
Species that aren't keystone species,
when they disappear, they don't
have a huge dramatic effect
on the stability of the ecosystem,
let me give you some examples.
The elephants in the savannah
are a keystone species
which is why we're so concerned about
the predation of elephants for their ivory
and killing them off because,
not because the elephants are predators
in the sense that they keep
other species' populations down,
but in fact, because
of the elephant's diet
on particular trees, they
keep the tree population down,
well, why is that
important in the savannah?
Well, the main food staple in the savannah
are essentially the grasslands,
and these grass is the main
food for most of the organisms.
If the elephants go away,
the trees do not have any type of check
on their overall growth
and they'll actually
out-compete the grass,
and so if you start having
more trees and fewer grass,
you have less food for all of the species
in the environment, and
that's why elephants,
though they form a very small portion
of the number of individuals
within its ecosystem,
exerts a very strong influence
on the community's diversity.
If you don't keep the
tree population down,
the grassland starts decreasing
and the food for all of the
organisms that eat that food
also starts decreasing,
has huge dramatic effects on
the stability of the ecosystem.
So, one of the things I
also want to bring up,
and this gets into evolution as well,
many of the things that
we see in evolution
have a lot to do with these
predator-prey relationships.
I told you that coevolution
typically occurs with competition,
but predator-prey
relationships has created
a number of fascinating
different types of things,
we've already talked a little
bit about some of these,
like camouflage, I mean,
look at some of these insects
that looked exactly
like their environment.
But again, this is situational,
take this insect into
a different environment
and it's no longer camouflaged, okay,
take the frog into a different environment
where they haven't had any exposure,
they may not understand
that warning coloration
that they're poisonous,
and so ultimately these are area-specific
where these processes
develop through evolution,
but they're not always advantageous
in any particular area.
Succession, now, when
we look at an ecosystem,
ultimately we want to ask the question,
is the ecosystem collapsing
or is it doing well?
When the ecosystem is developing
or has a setback but starts
to develop back again,
this is what we call succession,
so succession is essentially
how the ecosystem builds up.
But there are two ways
in which this can occur,
one is de novo, or from scratch,
and this is what we
call primary succession.
This is where there's no
development of the soil
so you don't get plants, you know,
these are areas that for
one reason or another
don't really have any life in them,
now there's not too many
places on our planet
that are like that, but
there are some places.
So here's what happens
with primary succession.
Ultimately it starts
off really, really slow,
the first thing that has to occur
is you have to start developing the soil.
That requires a particular
species called lichen,
remember, this is a combination
of both fungi and algae,
where the fungi, their
main job is decomposition,
the algae's main job is photosynthesis,
and so as, (coughs) excuse me,
as the sunlight generates
energy through photosynthesis,
through these algae,
and the fungi are able
to recycle the nutrients,
that starts the development of the soil,
but this takes a long time to occur.
As the soil begins to develop
other organisms can start invading,
you can have mosses, which remember,
are one type of plant that
are in these environments,
then you can end up having
much larger organisms.
As you start getting these larger plants,
you start getting other animals,
you'll get other types of organisms
that reside in these areas,
and then eventually it gets to the point
where there's a great diversity of life.
Now, not everything
develops into a forest,
if you look at a desert,
you may look at it and say,
well, there's not much life there
and you're right, compared
to other areas there isn't,
however, there still was a degree
of succession in the desert
where the organisms that are
adapted to that environment
are able to thrive and grow.
So succession doesn't mean that you reach,
you know, a certain number
of trees and other things,
it means when you reach
that end of the succession,
the environment is sustaining
as much life as it can.
A desert can't sustain as much
life as a tropical rainforest
because of the amount of
nutrients and water flow
and temperature and things of that sort,
however, both have had their successions.
Now, how long does this take?
Primary succession can take
hundreds and hundreds of years,
usually somewhere upwards of a millennia
for it to go from nothing to go to,
what we call the climax community, okay?
Now this occurs in aquatic
ecosystems as well,
but we're mainly gonna focus
on land for our purposes.
Now there's another type of succession
and this happens more readily
than primary succession,
it's called secondary succession.
So what is secondary succession?
Well, it's when an ecosystem bounces back
from some type of collapse.
A forest fire kills off
a good number of trees,
scatters a lot of the animals and whatnot,
you know, really destroys a lot of life,
however, look, the soil
is still developed,
there's still many organisms
that live in this environment,
it doesn't start from scratch,
and so this is much
easier to come back from,
usually on the order of,
say, a hundred years or so,
you know, a couple of
generations of various organisms
to get back to where it was before,
and in fact, in many cases,
the death of these organisms
is actually healthy for the ecosystem.
They found that when they didn't allow
parts of forests to burn,
you'd get these mega fires,
and they're finding now that it's actually
very healthy for certain parts
and so they do what they
call controlled burns
to be able to help reset
a lot of the things,
you know, nature creates
its own fires as well
and a lot of times we
don't let those happen
because we're living around it or whatnot,
but it's being taken care of itself
long before we were here and whatnot.
Ultimately secondary succession
is when it comes back
from some destruction,
where it's trying to reach
that climax community again,
but it doesn't have to
start from scratch, okay?
So this can be done from a forest fire,
this can be done from
some type of collapse
because of the
disappearance of a organism,
you know, an animal or whatnot,
but that's really the main difference.
Most everybody has heard
of the food chain, okay,
and when we talk about the food chain,
we talk about a linear relationship
from one level of the
ecosystem to the next.
Now in total, there are four
what we call trophic levels
within an ecosystem.
Remember how we talked about
autotrophs and heterotrophs?
That's what we're talking about here.
So each trophic level has a
distinct group of organisms
that belong to it.
The first trophic level,
and these are both
aquatic and terrestrial,
the first trophic level
are the autotrophs,
also called producers, why?
Because these are the photosynthesizers,
these are the ones that
bring all new energy
into an ecosystem.
We've talked many times
this semester about entropy
and how every time energy is transferred
from one organism to the next,
you never fully transfer all the energy
so energy is constantly
being lost due to heat,
okay, that's entropy.
That's why every ecosystem,
the foundation or the
stability of any ecosystem
is always on its producers,
on its autotrophs,
because without them, there is no life,
there is no way in which
an environment can survive
without photosynthesis.
Now yes, there are certain
places and locations
on our planet Earth in the
deep recesses of the oceans
that don't have any
photosynthetic activity,
but they are few and far between,
they usually live off of what
we call hydrothermal vents
where you have heat as a source of energy
and nutrients that come up from the gases
and other things like that
but they're very few and far between.
Most life essentially relies completely
on photosynthesis, okay.
So, on land, these are the plants,
in water, these are usually
the protists, the algae,
the cyanobacteria and things of that sort,
these all belong to the producers,
so just because we say
producers and autotrophs
doesn't mean we just mean plants,
we mean all producers,
all photosynthesizers,
all algae, all bacteria
that can photosynthesize
in the light, okay?
Now, notice it's a pyramid,
meaning there must be a great abundance
of these organisms for
any ecosystem to survive,
it can't be upside down, it
can't be top-heavy or collapses,
it must be bottom-heavy where
there's sufficient energy
production at its base
otherwise everything else collapses.
Now, the second trophic level,
these are where we start having
what we call heterotrophs.
Now, heterotrophs are just organisms
that must consume other
organisms to get their energy,
and pretty much these
three, these top three,
this is the animal kingdom, okay,
that's pretty much what's
in these top three,
because we're all heterotrophs,
we have to consume other
organisms to get our food,
but it depends upon what we consume.
So for example, if you are in this level
then you're pretty much an herbivore,
these are what we call primary consumers.
These are insects and other organisms
that are pure vegetarian, so to speak,
where they only eat autotrophs,
they only eat the producers,
so, these are what we call
the primary consumers, okay?
Well what if you don't like
eating vegetables, okay?
Secondary consumers,
these are ones that eat the
primary consumers, okay,
so like a bird eating an insect.
So insects, as we know, are animals,
in fact, they're one of
the most abundant animals,
and so really, secondary
consumers are carnivores,
if you eat insects, you're a carnivore.
So, a bird eating an
insect, or eating a beetle,
which eats a plant, that's
considered a secondary consumer.
And then, of course, you have
the top of the food chain,
notice the quotations
because I don't believe you,
you know, like kids
watching The Lego Movie,
the top is the tertiary consumers
or, you know, sharks,
eagles, lions, bears,
you know, any number of these organisms
that pretty much don't have
something that eats them,
so to speak, in nature.
But it's never really
this simple, you know,
when you actually look at the food chain,
it looks more like this,
it looks more like a
food web than a chain.
So when we study it, we study
it in a linear relationship,
but think about it,
you've got omnivores that
eat both plant and animal,
where do they fit in, you know,
and we're considered omnivores
because we have the capacity
to eat both plant and animal.
Some organisms can
solely eat other animals
and they don't have the
digestion for plant material,
others solely have the
digestion for plant material,
in which case they would
be just a herbivore
or a primary consumer,
but again, nothing in life is that simple
where we have a linear relationship.
That being said, you will be tested
on this linear relationship
and understanding it,
but just be aware that it's more complex
than what this actually illustrates.
But another thing that I
like about the energy pyramid
illustrates another
concept of energy flow,
because remember when we study ecosystems,
we not only study the living organisms
but the non-living,
which energy belongs to
in that type of a concept.
Notice that as you go up the pyramid
there's fewer and fewer organisms,
and that's due to the fact
that, not only due to entropy,
but also due to waste in,
think about how much you eat every day
and how much you defecate every day,
that is the proper word for it,
ultimately, you only extract
a tiny portion of the food,
why is that?
Well, because you don't have every enzyme
for every type of organic
material out there,
we can't break down fiber for energy,
we can't break down some
other types of substrates,
remember we even just
talked about the bacteria
can break down things that we can't
to be able to give us vitamins,
and so a lot of the biological
material that we consume
doesn't get incorporated into our body,
in fact, only 10% of what you consume
actually gets incorporated
into your system,
the other 90% goes away.
Well, it's not that that 90% gets wasted,
that's where this other
group comes into play,
where we have what are
called the decomposers.
The decomposers is made up of
many, many, many
different types of groups,
you have the animal kingdom,
the fungi, that's what mainly defines
the fungi kingdom, is decomposition,
you've got archaea, you've got bacteria,
the only kingdom that doesn't have
any decomposers in it is what?
What kingdom is devoid of
decomposers, do you think?
Remember we've got animal,
plant, protist and fungi.
What do you think?
No one, I know, we've got two weeks left
and everybody's like,
just tell me the answer.
Plants, plants are the only kingdom
that don't have any decomposers,
remember, plants are
pure photosynthesizers.
So, decomposers, protists,
you've got slime molds,
you've got worms and other
organisms in the animal kingdom
that are decomposers,
so decomposers aren't classified
as part of any of the trophic level
because they feed off of the dead
and the waste of all levels,
and that's why they're
in a group of their own.
So they're very important
for the stability of any ecosystem,
but they're not part
of these trophic levels
because of their relationship
where they don't actually
feed off of other organisms
but when a plant dies,
then they'll break down
into organic material.
When an animal dies,
then it'll break down as organic material,
or when a tree drops its leaves,
when it goes through hibernation,
it'll break down the
waste or the detritus,
it'll break down the feces
from any of these other organisms,
so ultimately decomposers
play a major role in recycling
much of the material that goes through us
that is not metabolized
and incorporated as a source of energy.
All right, now the second
half of ecosystem study
is looking at the non-living
components of an environment
and that comes down to things
such as nutrient cycling.
Now, we're gonna have to
jump back a little bit,
like back to lecture three
where we talked about atoms
and the more critical atoms for life,
what were those six basic
atoms that all life is made of?
- [Student] Carbon, nitrogen.
- [Lecturer] Remember
my little word schnops,
hey, carbon, hydrogen, nitrogen,
oxygen, phosphorus and sulfur,
these were the six fundamental
elements that you'll find
in every living organism on the planet.
Now they vary in as far as the
percentages and the degrees,
but every living organism
has these six basic elements.
Well, we mainly look at
carbon, nitrogen and phosphorus
because these are fundamental
for the stability of ecosystems.
When we talk about
nitrates and phosphates,
such as in fertilizer and whatnot,
that's really what we're talking about.
We don't have to worry
too much about carbon,
as we'll show in just a little bit,
but nitrogen and phosphates,
these are essential for some
of these key organic molecules.
As such, we look at how they're recycled
and maintained within an ecosystem.
Now, this looks very confusing at first
but we're gonna keep it nice and simple.
There's two main ways in which
organic molecules can be recycled,
they can follow a, what
we call sedimentary cycle,
where they remain primarily as a chemical,
they don't have what we call a gas state,
but there's also the gas
cycle of certain elements
like nitrogen and carbon and whatnot.
So some elements follow one,
some elements follow the other
and some actually do both, okay,
so we're gonna look at what role
some of these elements play.
So let's look at
phosphates, or phosphorus,
usually we don't really talk about
hydrogen, oxygen and sulfur
because they come along for
the ride for most of these,
especially when you're
dealing with, you know,
phosphates with a lot of
oxygen and things of that sort.
So phosphates primarily follow
solely a sedimentary cycle,
there is no gas phase of phosphate.
So their main way in
which they're recycled
is primarily through decomposition, okay,
so as organisms died,
as species are given off
and the decomposers break
down that organic material,
that goes right back into the soil
where the producers will absorb that up.
Now the same thing happens
in aquatic ecosystems,
except there's no soil in this case
but you still get the
production of nitrates
through decomposition that get recycled
within these ecosystems as well.
So nitr or, I'm sorry, phosphates,
phosphates are critical for the formation
of things like ATP in your DNA,
phospholipids that form the cell membrane,
things of that sort,
so phosphorus is one
of those key elements.
But there is no gas cycle,
so ultimately it just follows
through decomposition, okay,
so it follows a sedimentary cycle.
Now there is a problem today,
especially when we take these phosphates,
especially when we mine them out
and then add them, such
as a farmer might do.
If you have excessive phosphates,
this can actually disrupt
the balance of the ecosystem,
and so we'll see how that's
the case too with nitrates,
especially since we've been able to
artificially manufacture
nitrates from the atmosphere,
and a lot of that runoff that's come about
by the excess use of these phosphates
has caused a lot of problems
in certain ecosystems.
In fact, in China, a while
back, a couple of years back,
they had so much runoff from
a lot of the excess use of fertilizers
that they had mass algae blooms
that just disrupted huge coastal regions,
so thick that people could
actually lay on top of them
and not sink in the water,
so if you look that up,
algae blooms in China,
you'll see some news reports
probably from a couple of years ago,
but it was pretty nasty.
Remember those are the protists,
but they also thrive on phosphates,
and as they have those nutrients,
they're able to flourish very abundantly.
All right, so phosphorus primarily follows
a sedimentary cycle.
Let's look at nitrogen, okay,
again, lots of different,
crazy things going on here
but we can simplify this down.
Now, one of the things about nitrogen
is when left to itself,
nature pretty much regulates
the amount of nitrogen,
maybe not as fast as we'd like it to,
but it does have its way of regulating
the nitrates in the soil.
Nitrogen, again, is
important for amino acids,
nitrogen is a key part
of amino acids and such,
and so plants need these
nitrates in the soil,
they can't get it from
the atmosphere itself,
even though the majority of air
in which you breathe is nitrogen gas,
about 60% or so of the air
which you breathe is nitrogen gas,
but we can't incorporate the nitrogen
into our biological material
just by breathing it in.
If you're a scuba diver, a
deep sea diver, actually,
you know this rule that
you follow the bubbles up
because if you don't,
you come up too fast,
the nitrogen that you've been breathing in
essentially comes out of your cells,
forms bubbles in your blood
and can actually kill you.
So the nitrogen doesn't get
incorporated into your biology
just by breathing it in,
even plants can't incorporate the nitrogen
by bringing it in as a gas state.
So even though there's this huge reservoir
of nitrogen in the atmosphere,
it can't be utilized by any organisms
until it's been put into the soil,
so that's why nitrogen follows
both a gas and sedimentary cycle,
the gas cycle is it's reservoir,
the nitrogen or sedimentary
cycle in the soil,
that's where it becomes most useful.
Now there's a couple of different forms,
there's nitrates and there's ammonia,
both of these play key roles
in various organic molecules,
we're not gonna make too much
of a distinction between them,
but I do want to point out
two main groups of bacteria
that play a key role in recycling.
First, when there's not
enough nitrogen in the soil,
there are these bacteria that
live in the nodules of plants
called nitrogen-fixing bacteria.
These are the ones that take
the gas form of nitrogen
and turn it into the sedimentary form,
things like ammonia and there's
other nitrifying bacteria
that turn it into nitrates
but I'm mainly gonna focus on
the nitrogen-fixing bacteria.
Now, if there's too much
nitrogen in the soil,
again, as what typically
happens when we add
the artificial nitrogen
fertilizers that we put in,
then there is a way to get rid
of a lot of that excess nitrogen,
there are bacteria called
denitrifying bacteria,
these maintain balance by
taking that excess nitrogen
and turning it back
into nitrogen gas, okay?
So the nitrogen-fixing bacteria
take it from the gas to sedimentary form,
and the denitrifying bacteria take it
from a sedimentary form and
put it back in the atmosphere,
and this is how it maintains homeostasis
on an ecological level, okay?
One thing that they've shown
is that the nitrogen is
able to remain more balanced
when you just regulate nitrogen
primarily through decomposition
and the nitrogen bacteria being able
to bring it in from the atmosphere,
because when we add
excess amounts of that,
it starts disrupting the
balance of nitrates in the soil,
too much is not too good,
too little, obviously, the
plants don't grow as well,
but at the same time they've
shown experimentally over time,
if you allow for decomposition
to be the main recycler of nitrates,
the soil does a lot better over time
and the plants do as well.
But we live in a world
where we need it now,
so ultimately we still
end up using nitrates
or nitrogen fertilizers
that are artificially made
by converting nitrates into a,
we can fix it chemically into
these nitrates and ammonia.
Carbon follows primarily a gas cycle,
it doesn't mean that
there's not any carbon
that is in the ground,
however, when we look at
the recycling of a chemical,
we primarily look at how it gets back
into the ecosystem through the producers.
So with phosphorus it's through
the ground, sedimentary,
with nitrogen it ultimately
has to be converted
into a sedimentary form to be usable,
but with carbon, it needs
to be in the gas form, why?
What is the process that takes in carbon
and turns it into a chemical?
- [Student] Photosynthesis.
- [Lecturer] It's photosynthesis,
so it has to come in via the gas stage.
Yes, carbon is broken down in the soil,
however, it's not usable as
a carbon organic molecule
for the plants, the plants
don't absorb the carbon
and then incorporate it in,
they have to take it in
through carbon dioxide.
And so there is decomposition
of this organic matter
and that does turn it
back into carbon dioxide,
but ultimately it follows
primarily a gas cycle,
animals and such eat the food
and undergo cellular respiration,
we breathe out the carbon dioxide
and the plants pretty
much take it back in.
So this is one of the issues too,
is that by the burning of fossil fuels
and the excessive use of
carbons as a fuel source,
we're looking at higher
amounts of carbon dioxide,
and so ultimately that regulation
comes about by photosynthesis.
Plants will take in the carbon dioxide
through photosynthesis,
making more food for us,
so it's a key component in
the stability of any ecosystem
for it to have more photosynthesizers
than other organisms.
When we start reducing these
through deforestation and other things,
we start having some serious problems
in the various ecosystems.
Now, in aquatic ecosystems
the same thing holds true,
photosynthesis is the
process, even in algae,
in these protists and
photosynthetic bacteria and such
that are in the ocean,
when carbon dioxide
dissolves in the water,
it's still, it can be
taken up as a gas, okay.
Now, we don't have any
questions on the biosphere
but the study of the biosphere
is essentially looking at
the relationship of all ecosystems,
all terrestrial and
all aquatic ecosystems,
which is a huge endeavor to understand.
And this is where climate
change and other models
are trying to predict what's gonna happen
when one thing changes
here and changes there
and it's a huge complex system,
it's not very easy to work out.
But we should be concerned
about mass changes in that
because as I mentioned,
if organisms have too much
change in their environment,
it can't adapt,
you start having collapse
of various ecosystems
and there's a lot of fallout
that can come about it
to us as well from that.
But, mainly you're gonna be tested
on these three nutrients
and how they're recycled,
carbon, nitrogen and phosphorus,
these are the three types of questions
you'll have on the nutrient cycling.
