Hello marine biology students.
In this video we're going to start talking
about ecology of marine systems.
[Intro Music]
So, this week we're going to talk about ecology
and a bit about the intertidal and estuaries
as well.
So what is ecology?
Well, ecology 
is the interaction between organisms and their
environment.
These interactions 
affect the survival and distribution of organisms
in their environment and these interactions
can be very complex.
As we're about to start discussing ecology
in more detail, it would be helpful to have
a shared list of terms and to know the definition
of these terms.
To the first is population.
A population is a group of individuals of
the same species living together in the same
place at the same time.
It is assumed that a population will have
genetic exchange and that the offspring of
this population will represent the general
genetic makeup of the parents.
The next term to know is the community of
an area.
A community is made up of all the populations
of organisms of different species living in
a defined area.
So community is when you have organisms of
different species interacting with each other.
The term habitat is simply the physical place
where an organism lives.
And then lastly, when we talk about all of
the resources, both living and non-living,
biotic and abiotic, that an organism uses
for survival, growth, and reproduction, we
call that it's ecological niche.
So populations, populations are the smallest
biological units that can evolve.
Populations are groups of organisms of the
same species and populations require specific
resources to survive.
These resources can affect population growth
if they are in short supply, and resources
that affect the growth of a population are
called limiting resources.
Now, there are many things that a population
needs to survive and it could be that there's
such an abundance of some of these resources
that even if it's total amount is cut in half,
that's not going to change how the population
is able to grow.
So we wouldn't consider those limiting resources.
But, if there are other resources that if
this population is experiencing competition,
if it has to work to get these enough resources
from say maybe a different species or different
population entirely and its growth is affected,
if it's not able to get those resources.
Those are the types of resources we're talking
about when we say limiting resources.
And a variety of different things can be limiting
resources.
This can include food and nutrients.
It could be physical factors, such as light,
salinity, or even just surfaces or substrate
to live on.
It could simply be space or habitat, different
gases such as oxygen or carbon dioxide.
Limiting resources can also include things
like parasites, and other symbionts, so an
excess of parasites could limit growth or
an absence of essential symbionts could also
limit growth.
These are all factors which can control the
growth of a population.
And in this diagram, we can see exponential
growth of dinoflagellates.
If there is not a lack of any of these limiting
resources, then reproduction and population
size increase can happen, often in an exponential
manner.
However, eventually a population is going
to meet some sort of limit.
Even if a population is not checked by a limiting
resource, there is a maximum number
of individuals that any habitat can support,
and this number is known as the carrying capacity
of that habitat.
As populations become more crowded, the growth
rate of that population will decrease.
And here in this diagram, we can see how the
growth of a population of dinoflagellates
changes over time, but it can only approach
carrying capacity and as it approaches carrying
capacity the rate of population growth slows
down.
Through this and future lectures, we're going
to talk about the different ways that species
can interact with each other.
This can be through competition, where they
are competing for resources.
This could be through direct predator/prey
interactions, where one organism is feeding
on another.
Or it can also be through symbiosis, where
the organisms are living together.
Now symbiosis does also include certain types
of parasitism, so it's not always only beneficial.
So, we'll start by discussing competition.
Competition occurs 
when two different populations use the same
limiting resources that they both require
for survival.
Organisms can compete with members of their
own species, which is known as intraspecific
competition, or they may be competing with
members of other species and this is called
interspecific competition.
An interspecific competition, again, is that
competition against organisms of different
species.
So here we see an example of intraspecific
competition.
These two hermit crabs are competing for snail
shells in their environment to use as their
homes.
This particular example of competition is
quite fierce, as clearly one of these two
competitors has lost a leg in this conflict.
The number of available snail shells in this
environment is a limiting resource and it's
often these limiting resources that drive
competition.
An organism can use a resource at the expense
of another organism, meaning by using that
resource, one individual or even one population
will thrive and the other will be limited
because of it.
This may result in reduced ability of that
individual or even population to reproduce
or even survive.
Poorer competitors may die out due to this
competition.
Interspecific competition is when individuals
of different species
compete for the same resources, whether they're
competing for food or space or some other
limiting resource.
Now, the outcome of interspecific competition
is either that one species excludes the other,
meaning they simply out-compete them, the
lacking species or the less competitive species
is just not able to get enough of that resource
that it needs to survive, or they coexist.
They coexist by sharing a resource, by becoming
specialized.
So there's resource partitioning, or these
populations start using different aspects
of that resource.
And some can even change, either starting
to eat a different food or feeding at different
times.
By specializing and partitioning this resource,
it can allow species that otherwise were in
direct competition to now coexist.
So, we're next going to discuss different
methods of symbiosis or living together.
The prefix sym- means together, and bio- refers
to life, So, living together.
And examples of symbiosis can include mutualism,
meaning both species benefit.
Examples include cleaning associations on
coral reefs or zooxanthellae living within
coral polyps themselves.
Symbiosis doesn't always have to be endosymbiosis,
but endosymbiosis or organisms living within
the bodies of other organisms can happen.
Commensalism is another way that organisms
can interact.
In commensalism, one species seems to be receiving
benefit, whereas the other species isn't particularly
harmed or negatively impacted, but they aren't
specifically receiving benefit.
An example of this are barnacles living on
whales.
As we can see in this picture, there are several
barnacles living on the mouth of this whale.
Those barnacles are getting a free ride.
They're also being exposed to fresh water
and filter feeding, whereas the whales, they
don't really get much out of this.
So this is an example of commensalism.
But with that said, the whales aren't necessarily
harmed either.
The last category of symbiosis that we'll
talk about is parasitism.
Parasitism is a form of symbiosis in which
one species receives benefit and this does
happen at the expense of the host.
So examples, tapeworms within the guts of
whales.
The tapeworms are receiving all the benefit
of nutrients within the whale’s digestive
system and this is only negatively impacting
the whales.
The whales do not get benefit and in fact
they do not get to take advantage of all of
the resources that they are consuming because
of these tapeworms.
And occasionally, parasites can result in
illness and even death.
Now, rarely is it the goal of the parasites
to cause immediate death of its host, unless
it's simply an intermediate host and the parasite
is using it to get to another host, but the
parasite benefits as long as its host remains
alive.
So, in talking about cases of mutualism, where
both members of this symbiosis benefit, well
these symbioses can be facultative, in which
the partners receive benefits together, however
they can potentially live separate from each
other.
Or, it can be an obligate symbiosis.
An obligate symbiosis is when a partner could
not survive without their other partners.
In all cases, it's the smaller partner that
is known as the symbiont
while the larger partner is the host.
And here in this image we see a moray eel
at a cleaning station.
The eel is receiving benefit because smaller
fish are eating parasites off the surface
of its skin.
The smaller fish are receiving benefit in
that they're being fed and also the moray
eel is not here aggressively.
They aren't under threat by the moray eel
at this point.
So this is an example of a mutualistic symbiotic
association.
Predation is entirely different.
In predation, it's the predator who benefits
at the expense of the prey.
In predation, one species, the predator, kills
another, the prey, for food.
Prey species often have adaptations that help
them to avoid being eaten, such as warning
coloration, camouflage or mimicry.
In herbivory, an animal is consuming a plant.
So, the organism which we call an herbivore
and we extend the definition to include both
seaweeds and algae as well, the herbivore
eats that seaweed or that plant and so in
essence they are preying upon a non-animal
organism.
An ecosystem is all of the living, biotic,
and non-living, abiotic, components in a particular
area.
So the community and the abiotic factors together
make up the ecosystem.
While we identify ecosystems as a group, neighboring
ecosystems can interact with each other.
All ecosystems require a constant input of
energy and as we'll see, chemicals and nutrients
are cycled within and between ecosystems.
And that completes our introduction of how
species interact with each other.
Now in our next video we're going to talk
about energy flow and nutrient cycles.
And “Have you ever wondered how you could
be more efficient?”
Well, we'll talk about that in the next video.
