Download P_9.pulation - A group of organisms of the same species that live in

POPULATION TERMS
Ecolog.2 - the study of organisms and how they interact with their
environment.
P_9.pulation - A group of organisms of the same species that live in the same
area (and interact with each other).
Population Density - The number of individuals in a population per unit of area (ex. m2)
Community - a collection of interacting populations that live in the
same ecosystem. (the living portion of an ecosystem)
D_~ersion - The arrangement of organisms in a population within a given amount of space.
(the pattern of their distribution -~ ex. clumped, random, uniform)
a. clumped - Occurs when individuals tend to be grouped in clusters. The presence of
of one individual increases the likelihood of finding another individual
nearby. This patterncould be due to the presence of a natural resource
or certain social behaviors (e.g. forming herds and colonies for mating,
protection from predation, migration). Most common dispersion pattern.
b.random - Occurs when the presence of one individual does not directly influence
the location of any other individual. The spacing between ,individuals is unpredictable.
This pattern is more common in plants, but uncommon in ~nimal populations.
c. uniform - Occurs when individuals are evenly spaced within an area. The preseuce of
of one individual decreases the likelthood of finding another individnal
nearby. Animals may avoid each other due to territoriality or competition.
Fecundity - Physically capable of sexual reproduction
Fertilit~ - The actual number of offspring produced through sexual reproduction
Growth Rate - The change in the size of a population over a given period of time.
Biotic Potential - Refers to the fastest rate at which a specific population can grow
(if there were unlimited resources)
Reproductive Potential - The maximum number of offspring that members of the
population can produce. (it depends upon such factors as generation time, the age at
which an individual is able to reproduce, # of offspring produced, fecundity, ...)
Carrying Capacity - The maximum number of individuals, of a given species,
that an environment can support for the long term -~ the size of population would
not negatively impact the environment.
Logistic Growth - Growth rates that establish an equilibrium with environmental resources
and stabilizes around the carrying capacity. (S curve - restricted growth).
Exponential Growth - Growth in the size of a population in which the rate of growth increases
as the size of the population increases (J curve - unrestricted growth).
Overshoot- A population’s size greatly exceeds the carrying capacity of the environment.
It occurs when a species encounters a new environment with a stock of unexploited
resources that promotes reprodnction in the population. (these resources are being utilized
at a nonrenewable rate). Overshoot often leads to the degradation of the habitat, lowering
of the carrying capacity, and a catastrophic collapse of the population.
Limiting Factor - A condition that restricts a population’s growth.
Ex. space, food availability, lack of particular nutrient, pH, oxygen.
Environmental Resistance -IncIudes all the limiting factors that tend to reduce a population’s
growth rates and therefore determines the carrying capacity of
an ecosystem. Environmental resistance increases as a population
approaches the carrying capacity. Results in logistic growth.
Dynamic Equilibrium - The state of a system when it remains unchanged because two
opposing forces are proceeding at the same rate.
Niche - the specific role, function, and position of an organism in an ecosystem.
(the full range of physical and biological conditions in which an organism lives
and how the organism uses those conditions --+ includes where it lives, what it
eats, its range of environmental temperatures, ho~v it interacts with other organisms, ...)
Density-Dependent Factors - The way these environmental factors regulate the growth of a
population is directly related to the size of the population.
.,.
ex. predation, disease, parasites, food supply
Density-Independent Factors - The way these enviro~maentai factors regulate the growth of a
population is NOT related to the size of the population.
ex. frost, drought, salinity, acidity, natural disasters (fire, flood, volcanic eruption)
Interspecific Interactions - Refers to interactions between different species
ex. predator-prey, mutualism, commensalisms, parasitism
Intraspecific Interactions - Refers to interactions between members of the same species
ex. territoriality (marking territory, bird songs, aggressive behavior
competition
~2gmbiosis is a reiationship in which two different species live in ctose
association. There are three main types of symbiosis.
Mutualism (+/+) Relationship in which both organisms benefit from the association.
Ex. lichens (fungus and alga), cows and intestinal microorganisms
Commensalism (+/0) Reiationship in which one organism benefits
and the other organism is neither helped nor harmed.
Ex. whales mad barnacles
Parasitism (+/-) Relationship in which one organism benefits and the other organism
is harmed by the association. Parasites live in or on an organism and obtain their
nutrition at the expense of this host. (often without killing the host)
Ex. ticks and mammals, tapeworms and humans
SAMPLING TECHNIQUES
Researchers must consider wlai~h sampling technique would work best in particular situation,
determine the sample size and the number of samples (balancing desired accuracy with the need
to minimize costs, time, and effort), decide how to pick the sampling locations.
Mark - Recapture Sampling - This method for estimating population size is often
used for animals that tend to be highly mobile, eiusive, are frequently in areas that are
hard to access (therefore you would be unlikely to encounter them when sampling the area).
It.involves marking a number of individuals° returning them to the natural population,
and subsequently doing a second capture (many captured the second time may not be
marked). It is based on the premise that the ratio of marked animals to all animals captured
the second time (recaptured) is the same as the ratio of marked animals to all
animals in the population. Therefore we can use a proportion to estimate the size
of the population.
N=_MxC
R
N= Estimate of total population ’size
M= Total # of animals marked on the first capture
C= Total # of animals (marked and tmmarked) caught during the second capture
R= # of marked animals caught during the second capture (recapture)
After the first capture and before the second capture, the marked animals are given sufficient
time to redistribute themselves among the natural population, but no so much time as to allow
things such as mi~ation, birth rates, and death rates to alter the population size.
Quadrat (Plot) Samplin~ - Tiffs method studies the organisms in plots or quadrats. It is based on the premise
that organisms selected randomly will be representative of the larger population (there are
statistical guidelines for.determining the minimal number of quadrats needed). It is one of the
techniques commonly used for estimating the population size of plant commtmities or sessile organisms.
Plot can be used to estimate things such as population size, population density, and dispersion patterns.
It involves counting mad recordir~g the mtmber of different organisms in each quadrat.
Population Size = Total # of individuals (o~one species) from all sampled q~aadrats X Total # of Quadrats
(for one species)
# of all sampled quadrats
(in the ecosystem)
_0uadrat - A clearly marked sample area of known size that is used during ecological studies.
It can be any shape, but it is usually rectangular (sometimes circular). The size of the
quadrat usually depends upon the size of the species being sampled.
Populations becoming established in a new area for the first
time are often termed coloniTing populations (betow, left).
They may undergo a rapid exponential (logarithmic) increase
in numbers as the~’e are p~enty of resources to allow a high
birth rate, while the death rate is often low. Exponential growth
produces a J-shaped growth curve that rises steeply as more
and more Individuals contribute to the population increase. If the
resources of the new habitat were endless (inexhaustible) then
the population would continue to increase at an exponential
being added to the
population per unit
time Is large.
rate. However, this rarely happens in natural populations. Initially,
growth may be exponentia! (or nearly so), but as the population
grows, its increase will slow and it will stabilize at a leve! that can
be supported by the environment (called the carrying capacity
or K). This type of growth is called sigmoidal end produces the
logistic growth curve (below, right). Estabgshed populations
will fluctuate about K, often in a regular way (gray area on the
graph below, right). Some species will have populations that vary
little from this stable condition, while others may oscillate wildly.
as it begins to fill up the
environment. This is called
Envif6nme~tal re~ist~dce
Carrying capacity (K) :
popu!~t!on "oversh6ots the
carrying capacity. "
that can be supported by
the enyironment. ~ .. :
I~xpenential (J)
curve Exponential
Logistic (S) curve
As the population grows,
the rate of population
Increase slows, reaching
an equilibrium level around
the carrying capacity.
Lag
The population tehds to fluctuate aroufid
an ’equilibrium level’. The iiuctuations are
caused by variations in the birth rate and
death rate as a result of the population
density exceeding 9r falling below
c~.r~ying capacity.
¯ "
arly on,
Time
Time
Explain why populations tend not to continue to increase exponentially in an environment:
2 Explain what is meant by environmental resistance:
3. (a) Explain what is meant by carrying capacity:
Explain the impgrt~nce of carrying capacity to the growth and maintenance of population numbers:
Species that expand into a new area, such as rabbits did in areas of Australia, typically show a period of rapid population
growth followed by a slowing of population growth as density dependent factors become more important and the
population settles around a level that can be supported by the carrying capacity of the environment.
(a) Explain ~Nhy a newly introduced consumer (e.g, rabbit) would initially exhibit a period of exponential population growth:
(b) Describe a likely outcome for a rabbit population after the initial rapid increase had slowed:
5. Describe the effect that introduced grazing species might have on the carrying capacity of the environment:
Some mammals, particularly in highly seasonal environments,
exhibit regular cycles in their population numbers. Snowshoe
hares in Canada exhibit such a cycle of population fluctuation
that has a periodicity of 9-11 years. Populations of lynx in the
area show a similar periodicity. Contrary to. early suggestions
that the lynx controlled the size of the hare population, it is now
known that the fluctuations in the hare population are governed
by other factors, probably the availability of palatable grasses.
The fluctuations in the lynx numbers however, do appear to be
the result of fluctuations in the numbers of hares (their principal
food item). TMs is true of most vertebrate predator-prey
systems: predators do not usually cor{trol prey populations, which
tend to be regulated by other factors such as food availabifity and
c~imatic facto~. Most predators have more than one prey species,
although one species may be preferred. Characteristically, when
one prey species becomes scarce, a predator wi!l "switch" to
another available prey item. Where one prey species is the
principal food item and there is limited opportunity for prey
switching, fluctuations !n the prey population may closely govern
predator cycles.
(left) ever a ~0 ye&r pe 5d rev~a ed a
that was repeated ~ve~ 10 years or so.
~he oscillations in lynx numbers closely
matched those of the snowshoe hsre ’,~’
;
¯ ,.::. #
,,
system and the lynx are ve~ dependent
6n the h~res for food. Consequent y, the,
lagging slightly behisd those of th6 hare.
1, (a) From the graph above, date[mine the l~g time between the population peaks of the hares and the tynx:
(b) Explain why there is this time lag between the iacrease in the hare population and the response of the lynx:
2. Suggest why the lynx populations appear to be so dependent on the flqctuations on the hare:
3. (a) In terms of birth and death rates, explain how the availability of palatable food might regulate tile numbers of hares:
(b) Explain how a decline in availabl~ palatable food might affect their ability to withstand predation pressure:
Related activities: Predator-Prey Strateaies, Population Growth
Information about the populations of rare organisms in isolated
populations may, in some instances, be collected by direct
measure (direct counts and measurements of all the individuals
in the population), However, in most cases, populatiobs are too
large to be examined directly and they must be sampled in a
way that still provides information about them. Most practical
exercises in population ecology involve the collection or census
of living organisms, with a view to identifying the species and
quantifying their abundance and other population features
of interest~ Sampling techniques must be appropriate to the
community being studied and the information you wish to obtain.
Some of the common strategies used in ecologica! sampling, and
the situations for which they are best suited, are outlined in the
table below, it provides an overview of points to consider when
choosing a sampling regime. One must always consider the
time and equipment available, the organisms involved, and thd
impact of the sampling method on the environment. Fof example,
if the organisms involved are very mobile, sampling frames are
not appropriate. If it is important not to disturb the organisms,
observation alone must be used to gain information,
Point sampling
individual points are chosen an a map
(using a grid reference or random
numbers applied to a map grid) and
the organisms are sampled at those
points. Mobile organisms may be
sampled using traps, nets etc.
Systematic (grid)
Line transects: Tape or rope marks the Line. The
species occurring on the line ar~ recorded (all along
the line or, more usually, at regular Intervals). Lines
can be chosen randomly (left) or may follow an
environmental gradient.
Celt transects: A measured strip is located across
the study area to highlight any transitions. Quadrats
are used to sample the plants and animals at regular
intervals along the belt. Plants and immobile animaIs
are easily recorded. Mobile or cryptic animals need
to be trapped or recorded using appropriate methods.
Useful for: betermining spebies a~undance and eomr~nlt~ :
composition. Lf samples are large enough, popuJ~ti0n’
characteristics e.g. age structure, rep[od~)c~ive I~.a, rar~?~ta)~’
can be determined.
Considerati’o~s: Time efficient. Suitable for most organisms.
Depending on method environmental disturbance is minimal.
Species occur ng n low abur~dance may be missed.:’
Useful for: Well suited to determLning changes in ~0mmunity
composition along an environmental gradient, Wl~en p!aced. ’
andom y, they provide a quick measure of species occurr@nce~
Considerations for line transectsi "l~me efficient. Mo~t suitable;
for ptants and immobile or easLly caught animals. Disturbance
o the environment can be minimized, Species occurring in Low
abundance may be missed¯
: ;. : ~
well. Most suitable for plants and immobile er easily caught
animals. Good chance of recording most or all spe~ied, E~fo~s
should be made to minimize disturbance to the el~virddrn~nt!
Quadrat sampling
Sampling units or quadrats are placed randomly or
in a grid pattern dn the sample area.The occurrence
of organisms in these squares is noted, Plants and
slow moving animals are easily recorded. Rapidly
moving or cryptic animals need to be trapped or
recorded using appropriate methods.
Mark and recapture (capture-recapture)
Animals are captured, marked, and
then released. After a suitable time
period, the population is resampled.
The number of marked animals
recaptured in a second sample is
recorded as a proportion of the total.
mmob e species. Population should have a finite boundary,
Pe od between samplings must aLl6w ~or red!stribution Of
marked animals in the population. Marking shodld ~Jresen~ li~le :
1. Explain why we sample populations:
2. Describe a sampling technique that would be appropriate for determining each of the following:
(a) The percentage cover of a plant species in pasture:
(b) The density and age structure of a plankton population:
(c) Change in community composition from low to high altitude on a mountain:
2001-2007
ReLated acftvitles: Quadrat Sampling, Transect Sampling,
Mark and Recapture Sampling
Distribution and density are two interrelated properties of
populations. Population density is the number of individuals per
unit area (for land organisms) or voldme (for aquatic organisms).
Careful observation and precise mapping can determine the
distribution patterns for a species. The three basic distribution
patterns are: random, clumped and uniform. In the diagram
below, the circles represent individuals of the same species. It
can also represent populaiions of different species.
LowDensi~ ’ ’
@
O
O
O
aoart. There are on a few individuals per unff area or
vo ame (e.g. highly t~riitorial, s~olita-¢ mammal soecies
High Density
Clumped Distribution
0
O O Co @
Uniform Distribution
found a! ow densities
1. Describe why some organisms may exhibit a clumped distribution pattern because of:
(a) Resources in the environment:
(b) A group social behavior:
2. Describe a social behavior found in some animals that may encourage a uniform distribution:
3. Describe the type of environment that would encourage uniform distribution:
4. Describe an example of each of the following types of distribut!on pattern:
(a) Clumped:
(b) Random (more or less):
(c) Uniform (more or less):
Related activ ties Fea ures of Popu ations
ry few species show continued exponehtial growth. Population
size is regulated by factors that limit popul.ation growth. The
diagram below illustrates how population size can be regulated
by environmental factors. Density independent factors may
affect all individuals in a population equally. Some, however, may
be better able to adjust to them. Density dependent factors
have a greater affect when the population density is higher. They
become less important when the population density is low.
Directly or indirectly affect the food supply
Food supply
Rainfall
; Humid]~
Acidity
Salinity
Regardless of
population densi~
thes~ factors are
the same for aft
individuals.
The effects of
these factors are
influenced by
," Di~eas~
Parasites
omp~tit!001
Predati0~’
".. : Catastro : "
These factors are influenced by the
density of the population (Le. how
crowded the population Is).
: Fire.
. Drought
Organisms that are more crowded:
I~ Compete more for resources
¯ Are more easily !ound by
predators
i Spread disease and
parasites more readily.
Tsunami¯ ¯
.... Eatthq~.ke
Poor health or death
Increase is mortality
Change in ability to reproduce
Natality is affected
1. Discuss the role of density dependent factors and density independent factors in pol~ulation regulation. In your
discussion, make it clear that you understand the meaning of each of these terms:
2. Explain how an increase in population density allows disease to have a greater influence in regulating population size:
3. In cooler climates, aphids go through a huge population increase during the summer months. In autumn, population
numbers decline steeply. Describe a density dependent and a density independent factor regulating the populati£n:
(a) Density dependent:
(b) Density independent:
#;,l~t~,rl ~cfi~itle~: DensitY and Distribution