Community Ecology
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Community Ecology


Hi all Dr. Clark here again and today
we’re going to finish up ecology by talking about community ecology so we
talked about population ecology demography and things like that and now
we’re going to take that those components and kind of merge them into
the way in which we study communities and so a community college is fairly
important especially in to today’s setting where we have climate changes
and a lot of endangered species and deforestation habitat destruction lots
of human induced changes in the environment we’re not just interested in
how that affects a single individual population say snowshoe hare but rather
how does it affect the entire group of organisms within a given region so well
we’ll come back and we’ll look at this but this is a predator prey model the
Lynx hair model and you can see from this model you can see that as the Lynx
population goes up the hare population goes down as you would expect Lynx eat
the hair okay that population goes down so you can see here that the hair
population spikes and right after the spike of the
hair population there’s normally a spike of links that follows so hair population
increases by a lot the Lynx increase to consume the hairs because there’s lots
of nutrients they can produce more babies there’s a lot more food and then
the hair population crashes the Lynx population crashes hair rises etc
etcetera etcetera so it’s a fairly good fit okay and this
works great on things that are specialists like Lynx in this region are
specialists on snowshoe hares had we examined a different region a different
community college it wouldn’t be as is this because maybe the links in
different regions would eat more than just snowshoe hares maybe they eat other
types of rabbits or maybe they would eat you know some ground nesting birds and
things like that to supplement their diet so it wouldn’t be as nice and fit
but nonetheless when you’re just examining the community in this case the
predator prey dynamics sometimes you get these nice models that fit one another
and are highly predicted alright so a community like we talked about before
when we talked about community ecology it’s the number of species all the
populations within a given region and how they interact with each other now
like I said before when we’re talking early on about the redwood community the
community is normally distinguished or determined by some kind of dominant
species so what’s the primary dominant species in that community that’s what
the community is going to be called and that’s the characteristics that are
going to determine the community itself now can that change of course you change
that by having no changes to the habitat the temperatures and moisture the soil
ok those four components sunlight soil moisture and temperature that’s going to
determine what kin growth that’s going to determine what dictates your
community which also determines what species are going to be available to
live in that community we’re often interested not just in being able to say
ok that’s a community but what’s the interactions what is going on in the
community you know what produces the nutrients are the primary producers what
consumes those primary producers what consumes those individuals extender
extender etc and you know those kind of interactions so food web interactions
but also is their interactions from a parasitism
so are there parasites and what the parasites play is there an
interaction from mutualism or commensalism so do organisms help each
other out these kind of things and so all that plays a big role in determining
nutrient cycles or food webs and these kind of things that would dictate what’s
going on in the community okay so here’s a good example so we might examine a
watering hole okay in Tanzania and you might see a bunch of
organisms that are consuming plants so there’s a lot of plant habitat so these
are the primary producers these different trees and foliage things like
that and then you have things like zebras you know water buffalo or cape
buffalo giraffes other things that are in this region
consuming those plants so those are the primary consumers you even have some
birds like stilts and things like that that might be eating insects the insects
are also eating the plants the birds would be secondary consumers but then
what role do the Predators play so you have predators like lions and things
like that they would come into the community and they’re gonna play that
secondary or tertiary consumer and what rule and then what role do things like
organisms that might be occupying the region what role do they play in helping
some of these other individuals avoid predation
so here you can see some monkeys that are also visiting the watering hole with
this giraffe monkeys are known to be very good at alarm any alarming other
organisms of predators or disturbances so often monkeys will sound an alarm and
all the organisms that are watering would react to that and so that’s a way
of showing mutualisms all organisms benefit and the monkeys
are allowed to consume the water and sit around a but they’re also
sounding a call that every organism recognizes as kind of a predator call
and all organisms will leave so there are two views that kind of make up
community ecology on to and I don’t want to say competing views but they’re
they’re a little bit different from each other different ways of examining a
community the first one was put up by aj wilson and that is that a community
itself is from you should examine it from it the individualistic concept or
individualistic view in other words the community is nothing more than the
organisms that occupy that given area so there’s no overarching whole organism
you can’t think of a community itself as being viable because you can remove a
piece from that community and as still stay versus the epi comments point of
view and he he suggests that communities are a lot more than just a group of
organisms in the same given region and a bunch of different species and same
government region but it’s a holistic concept or holistic idea in that a
community itself is a super organism and if you change if you remove one
individual one species from the community you change the entire
community now you might still have a community but it’s a different community
than you originally had because they’re all integrated and you have things like
mutualism commensalism parasitism going on within the community and they you
need to think of the entire community as a super organism so it depends on what
view individuals have on how they are going to regulate
communities so if you’re individualistic view then it doesn’t matter if a single
species is lost to the community if your holistic view every single species is
just as important as the other and without those you wouldn’t have that
super organism well part of that goes into what we call niche or niche
competition so a niche is the abiotic so the nonliving and the living aspects to
a single place in the environment so where an organism can occupy that’s
considered their niche okay so that would be dictated by temperature
moisture soil sunlight what other organisms are present food all these
micro habitat information and that all determines where the organism can exist
and that’s their niche the word niche comes from a old english term for when
individuals rocks mr. mason’s would build things chimneys okay inside
a house like a fireplace they would leave a brick out typically they leave –
one on each side to match one on the right side one on the left side they
leave a brick out of the fireplace and it would create this little hole which
they call the niche and that niche you could stick you know matches or striker
or other things into that hole and that’s where you know where you’d have
kind of a place for those kind of utensils and that’s where the terms
niche came from and it’s a nice term for biological point of view also because
it’s really a specialized region or specialized area that only one organism
can occupy at a given time which brings us to competition if only a
single organism can occupy a niche at a given time then you’re going to have
competition for those niches and so two organisms that might want to occupy the
same niche will have to fight for it will have to either divide the niche
they’ll have to do something because no two organisms can occupy the same niche
you can have competition from an interest specific competition and that’s
between different species so different species that occupy a similar niches
would have interspecific competition or you can have intraspecific competition
and that’s going to be between same species just two individuals within that
same species so a lot of this comes about and when niches were first
discovered we started to really examine niches from point of view of there are
two types of niches out there you have a fundamental niche the fundamental niche
is all the places that an organism could occupy so theoretically they could
occupy it so the temperature the Sun the precip
care the soils whatever it might be in that region allow the organism to occupy
that region that’s the fundamental nature so basically it’s all the places
on the planet where that single organism could occupy
the realized niche is the actual place that that organism can occupy or is
occupying now the difference between the two is that realized niche take into
account competition are there other organisms that have the same fundamental
niche but they’re better at that fundamental niche they are better at
excluding individuals from that fundamental niche
so the realized niche is the actual place that the organism occupies take
for example two different types of barnacles so barnacles they’re going to
be attached to the rock surface and they they’re filter-feeding at this point
okay so water comes in they take nutrients out of the water and they grow
reproduce excetera to separate barnacles now we can look at one the Simha ballast
and we can look at its fundamental niche so simav annales fundamental niche is
identical to its realized niche but if we look at the mousies the mouse is a
different species of article much smaller can be displaced easier by simin
pinellas the families barnacle it’s fundamental niche is the entire region
okay so this is like a rock surface sticking out of the water so the mousies
could go deeper but they can’t because of the presence of the sim infernalis
barnacles and so they’re realized niche is much smaller than their fundamental
niche and that’s due to competition now we know this occurs because if we remove
semi-urban Alice the familis increases its range and it will go deeper until it
reaches its maximum which is similar to the maximum of semi-urban Alice and
there’s been a lot of research about competition or what we call a niche
competition and it’s a role in determining where organisms are in a
given region a lot of work by Gauss demonstrated this
competitive exclusion that I was just talking about or the principle of
competitive exclusion okay and this is actually where the term of no two
organisms can occupy the same niche at the same time really comes from and so
he examined lots of species but he examined species in competition around
resources and that resource could be food it can be space it could be water
it could be nesting habitat it’s it’s a resource that is limited in the
environment and he determined that no two species can occupy that same niche
so there has to be some kind of give-and-take in some cases it’s
competition and one group is excluded and the other one has to either retreat
or has the niche and the other one excluded from that niche or in some
cases they occupy half of the niche and that will lead to what we call resource
partitioning and we’ll come back to them so another example of this we can take
Paramecium Paramecium or little aquatic protozoan organisms and there are quite
a few different types and we can stick them in to a you know a bath of water
with nutrients and things like that and we can look at their populations and
their populations fit does sigmoidal graphs okay so the population starts off
small eventually reaches carrying capacity levels off okay so Aurelia we
can do that with that we can do it with cauda ada okay and the same thing you
get the same thing you can do it with Bruce Sarah a same different thing or
you know population is a little bit smaller but same thing sigmoidal graph
reaches carrying capacity and the levels off now what happens when we put them
together so if you put cañedo manner lea together
aruhya winds out it outcompetes good Adam
completely kadai them goes extinct in the population that’s true competition
competitive exclusion on the other hand if you put boosts area and kadai them
together they both reach carrying capacity the carrying capacity is much
less than what they were reaching previously they’re close to 150 so it’s
about half of what they were but they both can coexist at carrying capacity
and that means that they do what we call resource petitioning so a datum gets one
region and this area gets another region and so often when we examine communities
communities will work themselves out in the sense that competition is only good
for a little bit of time especially competitive exclusion is only good for a
little bit of time it’s often a waste of energy to compete and lose so what will
happen is species will try to avoid competition at all costs so they’ll try
to either occupy a region in which the other organism is not occupying at the
given time so they can avoid competition or they leave the region altogether
so when niches overlap and you have the same niches most of time you either will
have competitive exclusion where the winner takes all
or you have resource partitioning where the resources are divided so you create
two niches so again for Staind competition over a long period of time
rarely happens in natural communities because it’s extremely expensive
energetically speaking energetically speaking to occupy the
same niche is another individual and not overwhelm them exclude them or not
partition the resource it just creates fighting and a waste of energy so you’ll
often see in natural communities it’s either competitive exclusion so one
organism wins the other want retreats and is excluded from the region or
resource partitioning and it can lead to extinction of one individual otherwise
it could lead to a kind of a natural break or two niches being created
between the organisms and so here you can see an example of resource
partitioning so if we go to tropical regions and we can examine it like a
tropical tree of some sort we can start examining the different regions of the
tree and you can examine say the canopy of the tree and you might find this
Anolis species which is kind of blue and green and then I’m kind of matches the
canopy and then you can examine the trunk of the tree and you might find
this another species which would be brown and match the trunk of the tree
then you can examine the grassy areas around and you might find this species
and then you might find another tree as this species of analyst and so this is
all resource partitioning so these are nois lizards have the ability to avoid
competition by occupying small regions of the different types of trees or
vegetation in the reach in the area so resource partitioning kind of talked
about that now resource partitioning can happen in a couple different ways it can
happen from a sympatric speciation event or an area in which the organisms are
not I did so they occupy the exact same
habitat like the enola species that I just talked about okay that’s a simp
attrex species and they occupy the same habitat there’s nothing really dividing
them there’s no mountain range or anything like that they could occupy the
same region as each other they just don’t they partition the region oh
that’s very different than what we call allopatric species where they are
occupying the same niche but there’s something that divides them maybe
there’s a river that divides them maybe there’s a mountain that divides them
something divides those two species so they actually live in same niches and
they could be swapped you could move one species over the mountains and the other
side and they would occupy the same niche but due to either mountain range
River roadway something there’s some barrier that separates those two
habitats so those two are kind of different but can result in the same
resource partitioning it’s avoiding competition one is avoided by the
species partitioning and the resources themselves and another one is divided by
geographic area petitioning it so some ecological geographical event a river
road whatever it might be partitioning that out now when this occurs you can
get features morphology and physiology that differs so if you you know if we go
back to this picture here the lizard’s you can see that the morphology of these
lizards are very different none of them look identical to each
other and that’s what can occur when you get resource partitioning when an
organism has to occupy or is occupying a different niche or a different part of
the original niche then it will often have some selected
pressure on it so if the organism doesn’t match that background then maybe
it would be consumed by more predators so it’s advantageous for the individuals
that are reproduced that match the background they’re going to survive
they’re gonna have a distinct advantage and so in all cases you could get some
evolutionary evolutionary change that goes along with the resource
partitioning and that kind of brings us to things like coevolution so coal
evolution is an interesting concept in itself and that organisms have the
capability to interact with other organisms and adapt to other organisms
or adapt to competition or living with other organisms so if you’re always in
competition with it and other species for the same niche and you’re an
organism and you’ve evolved in an advantage then either this organism over
here that’s now at the disadvantage develops a mutation and evolves and and
is still able to compete with you or that organism goes extinct and so
coevolution is kind of this evolutionary arms race and things go back and forth
back and forth to kind of keep up in competition and there’s lots of examples
of this right classic examples of pollinators so the fact that a flower a
flower really would like an insect to just pollinate it doesn’t really want to
return anything to the insect so the nectar that a flower produces its
producing that to attract insects to it but if the flower can prevent the insect
from taking the nectar then the flower keeps its energy
and the flowers creating that nectar is creating that sugar so if the pollen
tube is deeper than the proboscis of the insect the insect will visit the flower
stick as proboscis down but not reach the nectar and but the insect will at
the same time pollinate the flower the insect on the other hand would like to
visit the flower without getting down into the flower and stick as proboscis
in take a sugar meal and leave as quick as possible so it can go to the next one
and keep consuming so this is an evolutionary arms race pollen tubes get
longer and suck proboscis cos longer okay or a different size or something
along those ranges predator-prey same thing
predators want to consume prey prey don’t want to be consumed prey develop
things like camouflage you know distaste poison glands been a
toxicity something like that predators developed the ability to consume things
that are toxic okay or the ability to see things that are in camouflage lots
of different ways that coevolution can happen symbiotic relationships where you
know organisms are working in unison and we talked about this before
things like termites having beneficial bacteria that you know live inside their
gut that allows them to break down cellulose the bacteria can’t live
outside of the gut the termite can’t live without the bacteria so you have a
symbiotic relationship okay so here you can see you know just that pollination
buybacks you can see that the rostrum or the nose of this bat is elongated okay
and it’s not showing you the tongue but the tongue is also long so the bat can
stick his head down into the flower the flower is also adapted you can see all
these antlers these anthers will put pollen all over in the organisms head
the back may have whiskers which can pick up pollen
okay and so it might be advantageous for the bat itself to pollinate more flowers
you pollinate more flowers you have more flowers to visit if more of this cactus
is species of cactus around and therefore you can have more meals
because the nectar is down in here and and on and on and on so kind of an
evolutionary arms race it’s not like this individual is thinking about
increasing the population cactus or this cactus is thinking about tricking this
back into consuming it it just happens that mutations that are beneficial to
this individual or beneficial to this individual are the ones that are passed
on and the ones that accumulate over time the beneficial mutations accumulate
the non beneficial ones typically cause the organism to be maladaptive or die
without reproducing and a symbiotic relationship okay where they talked
about organisms live in relation to each other now there are lots of different
type of symbiotic relationships some more beneficial to one organism than the
other like parasitism and in the case of parasites one organism the parasite is
benefiting at the cost of another organism mutualism and you get benefit
at no cost commensalism both benefit or at least in some cases they both benefit
so there’s lots of ways at which this can occur so here you can see mutualism
an example of both organisms potentially benefiting so this is some ants and some
aphids and mutualistic response here is that both species benefit from this
interaction or at least superficially when we examine it
they both benefit so Athens produce a little bit of what we call honeydew and
so they have little teeny for Coulomb that come off the back end of the aphid
and they excrete a sugary substance called honeydew the ants consume this so
the ants actually farm a fits so they’ll get the aphids and the ants will just
crawl over the top of them and they’ll protect them from predators so it’s
basically like the ants are milking these a fat cows and they’re getting all
the honeydew that’s coming from the aphids the aphids produced it the ants
don’t eat the aphids but the ants protect the aphids from things like
ladybird beetles and other things that would come in and consume the aphids
right so that’s a mutualistic point of view
now this is not mutualistic in the sense that they can’t exist without each other
though and these ants the species ants doesn’t have to farm aphids this a fit
does not have to be protected by this ant so in certain regions the aphids
exist just fine without the ant ant exist just fine without the aphids but
in other regions they do have this you know protection method plus a feeding
method for the ants parasites again like I said before one benefits to
the harm of the other now I hope you realize that parasitism is about one
organism feeding on another organism but it’s not predator prey it’s different
than an organism killing another organism in parasitism the parasite
normally does not kill its host and normally it just feeds off the host now
there are some examples when they kill the host
like for example per siddik wasps almost always kill the hoes
whether they’re parasitic was on things like tarantulas or or Lepidoptera
caterpillars and they lay their egg inside the egg eats the organism from
the inside out or the larvae eats the organism from the inside out and then
comes out okay in those cases of parasitism they do
kill the their host okay but most forms of parasitism most examples parts of the
organism just lives off its host for a little bit of time until it’s got enough
nutrients to reproduce and then it will leave the organism if it can most the
time the parasite is smaller than the host and you know remains associated
with those for a given amount of time so until reproduction or maybe their entire
life for example we have little teeny fuck-you almight okay that live in our
eyebrows in our eyelashes that live on us for our entire life and they’re minut
little teeny mites that almost every single person on the planet has them it
doesn’t matter how much you scrub you still have them and you’ll never know
that they’re really there okay but they live off of dead skin or dying skin and
maybe a little bit of blood here and there depends on the species
but they live off of us and we never know it we’re not losing a massive of my
energy to them they’re not causing disease disorders anything like that in
some cases they do cause infection but those are very rare so nonetheless we do
have parasites that live on us constantly okay and are associated with
us for their entire life now some of you might have had a tick on you before
that’s also a parasite it’s going to take a blood meal it’s going to engorge
yourself and then it’ll drop off and unless you just brush it off okay but if
it takes a blood meal it would encourage yourself don’t got
large enough and drop-off okay so in some cases
parasites will live their entire lifecycle with you or entire life
history with you or another organism in other cases it’s just for a quick blood
meal and then they’ll drop off and mate or whatever and find another host so
there are some different parasites out there normally we classify them in three
main class classifications either a parasite is considered an ecto parasite
it means it that it occupies the external surface of their host so like a
tick mosquito fuck you o mites chiggers lots of things that can occupy our outer
buck outer botflies these kind of things can occupy our outer surface so they
live on the outer surface etc you have internal parasites which we call endo
parasites and they often feed on the internal surfaces of their hosts so
things like tapeworms liver flukes guts loops
okay these kind of things live inside of you and have a different kind of life
cycle and then the final one is brood parasites and brood parasites are a
little bit different they don’t consume bodies but they consume resources so a
brood parasite is a good example is an example of birds that will lay their
eggs in another bird’s nest and so they will take their a the other birds eggs
out or maybe they’ll cover them they’ll eat them they do lots of different ways
to do it then they drop their own eggs in and then make another bird raise
their young that’s a brood parasite now there are
different forms of this and some people probably know humans that are brood
parasites like they say they can’t take care of their kids so they pass them off
to their parents or they say they can’t take care of their kids and they pass
them off to their siblings technically I guess that’s brood parasitism but it’s
also you know they’re not tricking you well most of times I’m not tricking you
okay in this case brood parasites normally they trick the host so the host
actually doesn’t know they’re taking care of some other organisms offspring
they’re just taking care of something so things like cuckoos they mimic the call
of babies that they’re laid in so this is tricking the parents to keep feeding
them there’s lots of different ways at which this can occur now commensalism is
interesting and it’s kind of hard to distinguish commensalism from mutualism
or mutualism from commensalism so a lot of examples that we would say is a
mutualistic relationship where both individual benefits are actually
probably a commensalism benefit or commensalism relationship where one
benefits and the other one’s not hurt or helped so things like you know clownfish
laying their eggs and in regions that have sea anemones or stinging sea
anemones the sea anemone itself gets really no benefit from the clownfish
laying its eggs there may be a little bit of benefit if it’s defecating in the
region and providing nutrients and things like that
but for the most part there’s really no benefit for the sea anemone but there’s
a benefit for the tropical fish and that you know their eggs are protected by the
stinging structure or stinging creature and there’s lots of examples that we see
of you know organisms that will benefit that come to really no hurt or no help
to the other benefit you know you see like feeder wrasse a little teeny fish
that feed inside shark’s mouth and pick food chunks out of them
things like that that’s an example of commensalism the shark actually doesn’t
need to have its teeth clean shirk lose their teeth constantly so they’re not
having cavities or anything like that from food being left in their mouth does
it come at a cost to the shark probably not very much there’s not much energy
benefit of a little teeny bit of food that’s stuck in your teeth and but it
comes out a huge benefit to the feeder wrasse because now they can you know get
a food meal that’s you know big enough to supply them energy so there’s lots of
kind of examples of that like I said before there’s really no clear cut
between commensalism and mutualism a lot of times we’ll say something is
mutualistic both individuals are benefit but it’s an actually example of
commensalism sometimes we say is commensalism but we don’t know and it’s
really a benefit to the species that we’re saying that doesn’t get hurt or it
doesn’t help okay so there’s really no clear cut between those two and it can
be hard just to distinguish them unless you know a lot about the species all
right so back to predator prey predators consume another organism the interesting
thing a lot a lot of times and a lot of studies have indicated that predators
are really good at just consuming all the prey species and then starving so a
lot of people especially in the region of Yellowstone Wyoming Idaho Montana
will say things like wolves kill for fun this is not the case they’re not killing
for fun they’re killing because that’s what they do they are predators on prey
and so they will kill and they’ll engorge themselves until they become
full then they’ll leave the rest of the meat and scavengers will come and get it
okay but they would kill everything in a single
area if they can and it’s just the way at which predation or predators are set
up they will kill everything humans are good at this
okay if you remember the passenger pigeon we killed them all just because
we could and a lot of them laid on the landscape and decomposed
we killed bison just because we could we’ve killed fur seals we’ve killed you
know numerous things just because we can’t rabbits Fox predators predators
that are not going to eat and really have no harm to us not doing anything to
us we’ve wiped them off the planet or out of regions just because we can so
often predation is just this distinctive response to kill that because you’ve
killed it before and it will provide you a little bit of resources and so often
this is the case and that’ll really give us an idea of population cycles because
predation is so extensive and so such a high pressure you can get these cycles
these situations where predation the Predators will literally eat every
single prey source or at least kill every single pretty source that they can
find to cause that price source to crash and then the Predators will starve and
they will crash and that’s what brings us to this Lynx hair cycle where these
predators you can tell you know Lynx are way up here these predators don’t have
to eat that many or sorry the snowshoe hares up here the Lynx is down here
predator doesn’t doesn’t have to eat all these but it does okay and so maybe it
doesn’t eat them maybe it just kills them okay the population will crash the
predator will crash and you get this cyclic event back and forth back and
forth alright so with that I’m gonna leave you
that’s the end of community ecology and next we’ll talk about behavioral ecology
and behavior and how some things avoid predation or how some things avoid
parasitism or how some things allow for parasitism how things sexually mate or
do have sexual behaviors to attract mates and a lot of other behavioral
mechanisms that are out there

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