Population Ecology II
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Population Ecology II


Hi all Dr. Clark here again for fish and
wildlife today we are going to talk about population ecology number two this
is just a continuation from the last population ecology lecture it’s going to
add a little bit more context to how fish and wildlife management deal with
population ecology or what role does population ecology in occur or what role
does it play in managing of populations so first off I just want to we’ll just
kind of review some of the things that we went over either in population
dynamics but also in population ecology and then I’ll hit some new stuff as we
progress now when we are talking about population ecology last time I was
talking about birth rates and death rates and how you can change birth rates
or um you know you might have a different cohort that has a different
birth rate or might produce different egg egg amounts or might have a higher
mortality or less mortality just depends on the organism for example we talked
about you know species of fish that when they’re young and healthy and vibrant
they might produce a lot of eggs and they might be a major contributor to the
population what we could say the opposite might be true for something
like ungulates or even birds where while they might be young they might only
produce a few offspring or maybe they produce offspring but that that
offspring is not very healthy because the parent doesn’t know how to either
protect the young or to care for the young very well when we’re talking about
fish raising of young is fairly rare in game
species of fish so we don’t normally deal with that we will talk about some
examples where that does that may play a role okay but even at that I want to
talk about a different way that you can change birth rates and death rates and
here are two examples so these here is an example of some wild pigs or
javelinas and in certain parts of the United States these organisms are out of
control they eat massive amounts of vegetation
and they will destroy crop fields they’ll destroy people’s property etc so
one management role or one purpose of Fish and Wildlife Management is
sometimes to knock back or decrease population size excuse me
and one way to do that is increase the amount of death rate compared to birth
rate so by having extended hunting seasons or no limit hunting seasons a
lot often in those kind of situations excuse me are geared towards trying to
diminish or decrease populations that might be out of control on the flipside
is adding to the population so here you can see a game and fish an officer who’s
throwing in fish stocking fish into this river system oh that is a way to
increase the population without natural birth however in some situations if
you’re stocking fish that you expect to return and have some kind of
reproductive rate it could be it could be you know in you know a lack of better
terms you could be killing two birds with one stone in other words you could
be increasing the population bite in or do
new individuals to the population stalk to the population but in return there
that some of that stock might reproduce also and so you might get some natural
reproduction out of your stock to individuals okay
these are ways at which you can change birth rates from kind of the natural
ecosystem we’ll talk a lot more ways as we progress throughout the semester and
you’ll get an idea of what’s going on okay so let’s jump into kind of
describing population growth mathematically this is going to be a
little bit of review mainly because we did this when we’re talking population
dynamics but I want to make sure that you guys understand the mathematical
equations and how in the future we’re going to manipulate certain things and
you’ll have to be able to memorize these equations or at least have them written
down to where you can go back and manipulate them very easily so remember
that in represents the population size or the total number of individuals of a
single species in an area at the same time or is the rate of increase or the
rate of growth that the population has and we’ll talk about different types of
ours and we already have okay and transit grade of growth means that
there’s no limit to it and then a actually calculated rate of growth means
that you’re taking into account the birth rate the death rate the number of
migrants coming in or leaving the population time okay and again like I
said before time is based on the species sometimes it’s represented in year like
year is the time measurement months possibly days even multiple years may be
a five year period a ten year period etc so we
oh that to the geometric grade of increase so this is best case scenario I
would be represented by this equation so the population over some time period is
equal to the current population at time 0 times the rate of growth for that time
period so pretty simple that’s considered exponential growth or
geometric growth rate and like I said before it has no limit however if you
remember back to my population dynamic lecture I said that all populations will
eventually have a limit they will eventually reach their carrying capacity
so that kind of brings us to when resources are scarce or slow that
exponential growth will slow and it will reach carrying capacity now carrying
capacity could be based on lots of different resources we talked about this
before it could be food it could be water it could be habitat nesting sites
it could be the amount of predators it could be diseases there’s lots of things
that can set that carrying capacity but again once carrying capacity is
approached or you’re getting close to it your growth rate or your growth curve is
going to move from a J curve which is the exponential growth curve into an S
shape or sigmoidal growth curve which is your logistic growth curve so logistic
growth again is represented by some time interval some population interval okay
and we know that now in our mathematical equation we have introduced K so this
equation is a little bit different it’s the same it’s the same equation as
before it’s just represented as a little differently okay so where you have R
this is calculated are typically so birth – death plus immigration –
immigration times your original population at whatever time times 0 that
is ok 1 minus n divided by K and so again as in approaches K this number
gets really small and this number gets really small which in return changes
your population size or your growth of the population deep well it doesn’t
decrease but the rate of growth decreases okay you can have decreased
rate of growth if your R becomes negative so if you have a negative R
your population could actually be shrinking versus increasing in size and
that does happen it happens often when populations overshoot their carrying
capacity or when humans get involved involved and we increase the death rate
over the birth rate or we take too many individuals out of the population and
there’s not enough to replenish the population ok so that’s kind of just an
overview of population dynamics that’s you know those are the equations that
I’ve given you before now let’s talk about some factors that can affect the
populations growth some of this is review and others will be new to you ok
so when we’re talking about logistic growth populations or populations that
have a carrying capacity which is all populations eventually but ones that
have a carrying capacity are often what we call density dependent that means
that as the density of the population changes typically as it increases the
rate of growth will typically decrease and so as you pack more individuals into
a given region the rate of growth will decrease
and this will this is often the case when we’re talking about places that
have limited food resources limited habitat resources limited water
resources okay you can reach these dense density dependent factors very quickly okay so some of the ways at which this
can affect a population can be through disease all right there’s a lot of books
out there currently about human populations and human populations are
edging towards our carrying capacity at least what ecologists believe the
carrying capacity of humans on the planet is okay so if you believe some
ecologists they say it’s 9 billion we’re at about seven point eight billion
people right now so we’re approaching our current capacity if it is nine
billion other biologists ecologists believe it’s closer to 12 billion that’s
the carrying capacity either way were we’re approaching it where we’re getting
up there as a population of individuals on this planet so what why I’m bringing
this up is there’s a lot of books out there that are interested in what
happens when humans reach the carrying capacity because we are the smartest
species on the planet or we have the capabilities the highest capabilities of
intelligence on the planet not necessarily always the smartest but we
have that capability what happens when we reach our carrying capacity a lot of
books have been written about this disease and we know that things like you
know that the flu epidemic the Black Plague
we know that times in human history when we’ve experienced
mass massive death due to disease it always hits the density or the most
dense regions the hardest and that should make sense to most people is that
the more tightly packed individuals are in a given region the easier it is for
diseases to move through those individuals you can also see
physiological stress right the more competition there is for resources the
more stress there is on organism whether that be human I mean go to Walmart on
Black Friday ok and tell me that you have no stress ok I mean unless you are
extremely good as stress management Black Friday at Walmart or really any
department store can can really cause some physiological stress to individuals
increased heart rate and there’s a lot of actually evidence of this there’s
been many people that have been hooked up to monitors and then go to you know
events like Black Friday or you know large social events rallies these kind
of things and just experience the high density of individuals in one given
region and you can see the physiological stress on those individuals the other
thing that it can do not from a human point of view but from other organism
point of view is it can really increase predation rates by the the more tightly
packed individuals are the easier for predators to get a prey item so so the
other thing that can occur is you start to see these density dependent factors
like disease parasite load physiological stress pray start
predation starvation these kind of things as the population increases they
intensify so yes you might have disease that occurs in low-density populations
of course you are going to have disease but as you increase the density of that
population you’re going to increase the rate of disease so other things that can
occur are density independent factors we talked about this just a little bit
before and that’s things that really whether you have a drought or a fire or
a hurricane or tornado weather that Strutz strikes a specific region is
rarely due to the density of organisms in that given region now there has been
some evidence that suggests that you know droughts fire tornadoes and some of
these other things are more intense in regions where there’s high populations
and that’s because we at least high populations of humans and that’s because
we alter the ecosystem and so we get changes in the environment in the
environment around those ecosystems so for example if you ever look at a
thermal map of the United States you can see where all the major cities in the
United States are and that’s because these are thermal environments that are
that are much more warm than the surrounding environment and that’s due
to asphalt and concrete and all these other features that we have that absorb
heat and hold heat a much better than say you know grass or trees or even just
bare soil and so you can get these heat pockets
around these cities and that can change the weather system okay in a given
region and and there’s pretty good evidence that suggest increases in
tornadoes and things like that can be due to the more concrete and more
asphalt you have in a given region can intensify the not just the amount of
tornadoes you have but the severity of tornadoes
okay so density independent factors however often are not selecting for you
know how many individuals are in a given region okay whether or not a fire breaks
out or something like that the direction that the fire travels has
nothing to do with the density of the individuals now whether the fire occurs
or not can have an a you know a density dependent effect I mean obviously the
more individuals from a human standpoint you know the more individuals you have
in a given region the higher the likelihood that one of those individuals
is going to start a fire this is true okay but humans aside when we talk about
density dependent and density independent of factors most the time
droughts fire weather is density independent density dependent is things
like disease predation parasitism starvation those kind of things okay so
that brings me to talk about our selected and K selected species and now
when we’re talking about these different kind of ways to group species um I want
you to think about specific examples of organisms that you know you would say oh
that’s an R selected species okay so in our selected species typically has a
very high mortality rate as offspring so it produces lots of offspring high
reproductive rate lots of offering but not very many of the offspring actually
survive they’re also normally categorized by having very little
parental care so it’s basically just shoot out all your babies and leave and
the ones that live great they’re the ones that don’t carry the genetics on
and the ones that don’t they’re food for something else right so that’s an R
selected species K selected species typically a very low reproductive rate
so much lower reproductive rates they have a slower growth rate and they
normally exercise pretty heavy parental care I guess you could say or a lot of
parental care or at least it’s a lot of prenta care for a small period of time K
selected species are typically close to the carrying capacity so because they
have very low reproductive rates a few individuals here and there is not going
to make you balance over the carrying capacity our selected species on the
other hand they often are situated with what we call boom boom bust populations
so you might have good food resources good water resources etc at a given time
that population might explode and overshoot its carrying capacity out over
consume the food resources and then crash okay K selected species rarely do
that it normally takes them a very long time before they reach carrying capacity
they sit at carrying capacity for a long period of time then they occasionally
bounce over it or you know under it but you don’t have these big busts that you
often see in our selected species okay so a couple other things about our
selected species typically they’re shorter and lifespan and they have
earlier maturity they often are better at adapting to unstable environments
mainly they’re lower on the trophic level meaning their food for a lot of
other things normally K selected species K selected species pretty much the
opposite of our selected species longer life spans later maturity they adapt
well to stable environments but have a hard time when the environment changes
and they’re normally in the individual that’s consuming our selected species okay so remember when we say growth rate
is the product of birth rate plus immigration we can write it this way too
so birth rate plus immigration – death rate plus immigration so you have the
number of individuals coming into the population either from births or
migration – the number of individuals leaving the population either through
death or emigration out so first the number of births that occur in a
population in any given time whether I talked about that immigration number
individuals moving into the population we already talked about this death the
mortality okay the number individuals leaving via death and a given amount of
time and emigration or leaving the population moving to another population
we’ve already kind of you know hit on this pretty hard I just wanted to really
show you that you can write these equations in different forms when I
originally wrote it for you I wrote it R is equal to B minus D plus I minus e
yeah but you can write it as B plus I minus D plus e so just be
that equations might not always be identical to the way that you originally
saw it so you might have to use some algebra to convert that equation to
something that you remember or you can just use the equation as it stands if I
give you an equation you know that the equation is legitimate and that’s an
equation that you can use to calculate whatever it might be in this case growth
rate okay we talked about this a little bit lifespans you know this is the
amount of time or how long a given individual will last and it depends on
well first of all it depends on if here are selected species or K selected
species but even within K selected species or our selected species there’s
a huge range of life expectancies and they will also be determined by the
ecology or the environment that that organism lives in so you might have a
life expectancy of a certain species of rabbit you know might be four or five
years in one population but in a ecosystem that might have lower predator
predation rates it might have lower disease rates and higher food resources
you might see that the life span for that organism is maybe eight nine years
in that other ecosystem okay so normally what we will report for a given organism
or what we’re interested in in a given organism is their maximum lifespan so
this is the oldest that any individual within that species has ever lived
and so the oldest organism on the planet is Bristlecone pines and they live up to
four thousand 600 years maybe even longer than that we
don’t know because they’re hard to age I’ll talk about ageing trees a little
bit later on mainly because you can age fish and indeterminate growers species
that grow forever basically continuously grow throughout their
lifetime they grow or they have a pattern of growth very similar to trees
and you know I’ll talk more about this as as we progress and we start looking
at how to age organisms but nonetheless Bristlecone Pines they’re hard to age
and you know it’s not worth cutting the tree down to get an age because you
ended the organisms life so there’s no other methods that we can do this and I
highly suggest watching this YouTube video on Bristlecone pines they’re kind
of a neat organism neat tree and it gives you some information about some
researchers that may or may not have made some major mistakes when trying to
age Bristlecone Pines and all that you watch that if you if you so choose so
humans I’m not entirely sure what the oldest individual to ever live was like
how old they were but it’s somewhere around 120 years I get give or take a
couple years I’m not entirely sure okay and then if we’re talking about things
like you know a lot of the diseases or the microbes that might be affecting
fish and wildlife and they might only be alive for a couple hours but given their
population sizes it really doesn’t matter if that bacteria dies because a
new one has already been reproduced tenfold hundredfold a thousand fold over
so some micro microbes can only live for a few hours okay so the difference is in longevity
award kind of the lifespan or the I guess you could say the allocation of
energy to a lifespan can be represented in what we call survivorship curves
there are three general survivorship curves they’re called different things
but normally you have a type 1 survivorship curve or type a
survivorship curve and that means the organism is has a very long life it
survives very well from childhood all the way to adulthood now once it reaches
close to that maximum life span then you have a huge drop-off almost no organism
make it past a you know a maximum life span but they have you know low birth
rates typically and they just last for a long time so elephants bears humans etc
you know pretty much if the organism survives through childhood it’s pretty
much has the exact same survivorship throughout the rest of its life until it
reaches its maximum lifespan and then it starts tanking really fast okay type 2
or type B survivorship curve is the probability of death is really unrelated
to age it’s basically a constant death rate and most birds fit this pattern a
lot of other small mammals will fit this pattern and that means basically if your
death rate at Birth is 10% then your death rate when you’re 2 years old is
about 10% and when you’re 5 years old it’s about 10% and and the death rate is
really unrelated to age it’s just a constant death rate so you normally get
kind of a straight line or your curve is pretty straight
okay and then type three or what’s sometimes called type C survivorship
curve would be mortality is extremely high young in life and then you have a
fairly consistent death rate throughout the rest of your life until you reach
your maximum life span so high mortality and then it’s pretty constant and I’ll
show you don’t this curve here so here you can see you know type 1 or type a
you have this fairly constant survivorship until you reach close to
that maximum and then you just tank as as a population so you know I think the
human population our life expectancy is somewhere around 80 years old 78 80 it
depends on the sex of the individual okay after that it’s you know your death
rate is is increasing at least as a population after basically 80 boom
starts to tank but up to that point it’s pretty good it’s pretty constant okay um
B so most birds etc okay it’s it’s just a straight line down I see or type 3
okay this is like a lot of fish a lot of insects a lot of plants produce massive
amounts of young a lot of them die the ones that survive survive at a constant
rate until they reach their maximum lifespan okay so that brings me to a
little bit more about populations and how populations interact with each other
okay or between populations or within a population so that there are two terms
for this intrinsic factors intrinsic factors
are between individuals of the same species normally between individuals in
the same population so this might be competition for food resources
competition for mates ok competition for habitat etc those are intrinsic factors
that happen you know within a population between the same species extrinsic
factors are from outside that population sometimes it can be the same species
other times it can be interest specific factors or another species that is
affecting them from outside it could be a predator or something like that biotic factors are factors that occur
from living organisms so biotic meaning living so most of time like I said
before these are density dependent abiotic factors a in in biology means
non so abiotic meaning nonliving okay these tend to be density independent
have we talked about this before again these are weather related typically
whether that be you know temperature humidity precipitation wind you know
whatever it might be those are abiotic factors all right so
density dependent factors there’s a couple situations that I want to talk
about when we talk about density dependent factors and the role of
managers might play in such events ok if we have huge populations populations
that we see that may be disease is fluent in the population okay or running
rampant in the population may they’re destroying lots of crops maybe
there’s a lot of malnourished individuals these kind of things then
density is out of control typically from the managers point of view so ways at
which we can manage that from a density dependent factor is to try to reduce the
population size by either decreasing the number of individuals that are born
sometimes we do this by trying to do sterilization events those kind of
things or by increasing mortality okay so those are really the two ways that we
can do this change the birth rate or increase the dearth death rate and
here’s an example of increasing death rates so here you can see a couple
hunters and a whole pile of snow geese okay and a couple years back I shouldn’t
say a couple maybe ten years maybe more than that maybe twenty years ago there
is a huge population explosion of snow geese and snow geese had basically
became right at their carrying capacity and doing massive amounts of damage to
cropland etc and so Game and Fish at many different states came together and
they decided hey we’re going to have snow goose hunting seasons in the fall
you rarely see snow geese because they’re on their wintering grounds
already and you really don’t see them very often but in the spring you can see
huge amounts of snow geese and so they would often most states and they still
do this in a lot of states they offer spring hunts on snow geese okay and off
it’s regulations are are changed so they often have no limit on the snow geese
they did again it depends on the state but a lot of states mimic the same
regulations okay so no limit you can shoot as many snow geese as you want you
can use more than three shells in your shotgun and so you can remove the plug
in your shotgun and use six shells a lot of states allow you to electronic call
okay and just other regulations that normally don’t you can’t do during a
typical huntin season and those are management programs from the point of
view that the population has been deemed over populated or too many individuals
and the management is to reduce the population okay so there’s other
situations where this is kind of a natural situation where you get predator
to prey oscillations and we talked about this before when we were talking about
the Lynx hair cycle etc and you get this predator prey oscillation and that
happens inter specifically between two species um so you don’t have you know
this you don’t have this situation where humans have to step in you know that the
Predators are going to rebound and take out the prey numbers because the preys
you know has exploded that’s what we were actually hoping with snow geese as
the population increased we were hoping that the Predators might increase and
take out a lot of the young snow geese and things like that but it didn’t occur
so managers felt like they should step in and reduce the population the hunting
seasons it makes a lot of hunters happy um does it work we’ll come back to some
of these management decisions and we’ll look at
how long they’ve been running and whether or not they work okay but
nonetheless that is a result of a density dependent factor other density
dependent factors is intraspecific competition between individuals here’s a
great example of that there are populations of deer white-tailed deer
and mule deer in certain regions that the populations are so high that you
have huge events of starvation during winter time because there’s that
competition for food resources these populations just get out of control you
can have very large amount of deer dying over winter due to starvation disease
etc and um part of that has an its density dependent but a part of that is
the intraspecific interaction between individuals they’re competing with each
other for food resources typically um so again like we talked about before as a
population density is approaching carrying capacity a lot of what’s making
that carrying capacity set is you know certain resources it could be more than
one resources it could be food and water it could be food and shelter water and
shelter whatever it might be but as the population is reaching carrying capacity
you know that those resources are becoming limited okay and you can start
to see some changes in the population starvation hypothermia because there’s
no shelter yeah lots of things that can occur again depending on the species you
might see increases in you know territories or territorial defense and
so you might see as resources become more limited organisms spend more time
species spin more time defending their resources
against rivals this happens a lot in birds so birds as the density increases
they’ll defend their nest sites and to the point where if the density is high
enough males will defend the nest site and won’t reproduce so they’ll sit there
and defend night and day every every second of the day
and they won’t reproduce because they don’t have any time to reproduce because
they’re defending their territories against rivals that want to encroach in
on their territory and that has to do with that interest specific interaction
between individuals of the same species within the same population okay this can
also increase the stress related diseases okay again if heart rates are
up if tensions up okay if the amount of energy is needed to fight off diseases
is not there that can cause individuals become sick now you’re right next to
another individual which can cause them to be sick etc etc etc and you get the
stress-related diseases that often happen as populations reach those
carrying capacities okay alright so that’s kind of the last little bit of
what I want to talk about with population ecology we’re gonna move into
talking about the history of Game and Fish real quick just because I want to
after midterms I want to concentrate mainly on techniques that occur in game
in fish and wildlife management techniques for many different things
techniques for aging populations calculating calculating population sizes
mark recaptures so how do you capture them how do you mark them how do you sex
individuals these kind of things so after midterms that’s going to be the
concentration is we’re gonna really dive into some
those techniques you see a lot more videos of hand on techniques me
demonstrating how different how different techniques are carried out and
and whatnot okay so next time the history of Game and Fish

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