1.
Population EcologyPopulation Ecology
Cyra Mae R. Soreda
2.
Population EcologyPopulation Ecology
Population ecology is the study of
populations in relation to the
environment. It includes environmental
influences on population density and
distribution, age structure, and variations
in population size.
3.
Characteristics of PopulationCharacteristics of Population
Population size
Population density
Dispersion patterns
Demographics
Survivorship curves
Population growth
4.
Population sizePopulation size
“In population genetics and
population ecology, population size
(usually denoted N) is the number of
individual organisms in a population”.
Factors that Govern Population Size
1.Crude Birth Rate (CBR)
2.Crude Death Rate (CDR)
3.Immigration
4.Emigration
5.
Factors That Increase Population Size
1.Natality is recruitment to a population
through reproduction.
2.Immigration from external populations e.g.
Bird migration.
Factor Reducing Population Size
1.Mortality which is the death rate from any
source e.g. predation.
2.Emigration, where individuals leave the
population for another habitat.
6.
NatalityNatality
The production of new
individuals by birth, hatching,
germination or fission
2 aspects of reproduction must
be distinguished:
Fecundity
fertility
7.
NatalityNatality
Fecundity-physiological notion that refers to
an organism’s potential reproductive capacity
Fertility-ecological concept based on the no.
of viable offspring produced during a period
time
Realized fertility and potential fecundity-we
must be able to distinguish between them
8.
NatalityNatality
E.g, realized fertility rate for a
human pop may be only 1 birth per
15 years per female in the child-
bearing ages
While the potential fecundity rate
for humans is 1 birth per 10 to 11
months per female in the
childbearing ages
9.
MortalityMortality
Biologists-interested not only in why
organisms die but also why they die
at a given age
Longevity-the age of death of
individuals in a population
2 types:
◦ Potential longevity
◦ Realized longevity
10.
MortalityMortality
Potential longevity
◦ The maximum life span of an individual of
a particular sp is a limit set by the
physiology of the organism, such that it
simply dies of old age
◦ The average longevity of individuals living
under optimum conditions
◦ However, organisms rarely live under
optimum conditions-most die from
disease, or eaten by predators or succumb
to a number of natural hazards
11.
MortalityMortality
Realized longevity
◦ The actual life span of an organism
◦ Can be measured in the field, while
potential longevity only in labs or
zoos
12.
examplesexamples
European robin has an average
life expectation of 1 year in the
wild, whereas it can live at least
11 year in captivity
13.
Have more births than deaths?
◦ Population increases
Have more deaths than births?
◦ Population decreases
Have equal amounts of births and deaths?
◦ Population remains constant
What happens to the populationWhat happens to the population
when we….when we….
14.
ImmigrationImmigration
“im”= in
Migrate= to move from one place to
another
Immigration is the individual movement
into an area
Animals in search of mates and food in
new areas
15.
EmigrationEmigration
“E” means ‘out’
Migrate means to move from one
place to another
Emigrate means individuals moving out of
one place and into another
Young wolves and bears leaving as they
mature
Shortage of food
16.
NATALITYNATALITY
The birthrate, which is the ratio of total live
births to total population in a particular area
over a specified period of time
MORTALITYMORTALITY
The death rate, which is also the ratio of the
total number of deaths to the total population.
IMMIGRATIONIMMIGRATION
The number of organisms moving into area
occupied by the population is called
immigration.
EMIGRATIONEMIGRATION
The number of organisms moving out of the
area occupied by the population is called
emigration.
17.
How to estimate populationHow to estimate population
density?density?
Techniques differ between organisms
such that the technique to estimate deer
cannot be applied to bacteria or protozoa
or vice versa
There are 2 fundamental attributes that
affect and ecologists choice of technique
for population estimation
18.
2 attributes
Size
-small animals/plants are usually more abundant
than large animals/plants
Mobility
-based on movements of these organisms
19.
Why the need to estimateWhy the need to estimate
population density?population density?
Estimates of population are made for two
reasons:
◦ How to quantify nature – ecologist role
◦ Estimates are allows for comparisons between
different populations in terms of space and time
measure
20.
2 BROAD APPROACHES TO ESTIMATE POP DENSITY
Absolute density
No of individual per area/ per volume
Important for conservation and management
Relative density
Comparative no of organisms
Two areas of equal sizes, which area has more organism
e.g, between area x and y
Area x has more organism than area y
21.
ABSOLUTE DENSITYABSOLUTE DENSITY
Making total counts and by using
sampling methods
Total counts - direct counting of
populations
- human pop census,
- trees in a given area,
- breeding colonies can be photographed
then later counted
- in general total counts are possible for
few animals
22.
Measurements of Absolute densityMeasurements of Absolute density
Sampling methods
◦ to count only a small proportion
of the population - sample
Using the sample to estimate
the total population
2 general sampling techniques:
1) Use of quadrats
2) Capture-recapture method
23.
Use of Quadrats
Count all individuals on several quadrats of known size,
then extrapolate the average count to the whole area
Quadrat- a sampling area of any shape (may be a
rectangle, triangle or circle)
3 requirements:
• the pop in the quadrat must be determined exactly
• area of the quadrant must be known
• quadrant/s must be representative of the area
• achieved by random sampling
24.
Quadrant sampling in plantQuadrant sampling in plant
populationpopulation
Conduct a transect in the upland
hardwood forest
3 transect line, 110 meters long, count all
trees taller than 25cm within 1meter of
each line
By utilizing the quadrant method sampling
for old trees and seedlings, we can
determine if populations were likely to
change over time
25.
Capture Recapture Method
Capture, marking, release, and recapture-important for mobile animals
Why?-it allows not only an estimate of density but also estimates of birth rate
and death rate for the population being studied
Capture animal, mark (tag) them and then release them
Peterson method:
Involves 2 sampling periods
Capture, mark and release at time 1
Capture and check for marked animals at time 2
Time intervals between the 2 samples must be short because this method
assumes a closed population with no recruitment of new individuals into the
Population between time 1 and 2 and no losses of marked individuals
26.
Formula for capture-recaptureFormula for capture-recapture
methodmethod
Marked animals in 2nd
sample = Marked animals in 1st
sample
Total caught in 2nd
sample Total population size
27.
e.g of capture recapture methode.g of capture recapture method
Dahl marked trout in small
Norwegian lakes to estimate the size
of the population that was subject
to fishing. He marked and released
109 trout, and in 2nd
sample a few
days later caught 177 trout, of which
57 were marked. From the data,
what is the estimate population size?
28.
e.g of capture recapture methode.g of capture recapture method
By using the formula
57 = 109
177 Total pop size
Total pop size = (109 X 177)
57
= 338 trout
29.
RELATIVE DENSITYRELATIVE DENSITY
Traps – no caught per day per trap –
animals caught will depend on their density,
activity and range of movement, skill in
placing traps – rough idea of abundance –
night flying insects, pitfall traps for beetles,
suction traps for aerial insects
Fecal pellets – rabbits, deer, field mice –
provides an index of pop size
Vocalization frequency – bird calls per 10
mins, can be used for frogs, cicadas,
crickets
Pelt records – trapper records dates back
300 years – of lynx
30.
Relative densityRelative density
Catch per unit effort – index of fish abundance –
no of fish per cast net or no of fish per 1 hour
trawling
Number of artifacts – thing left behind – pupal
cases of emerging insects
Questionnaires – to sportsmen (eg fish)and
trappers
Cover - % ground surface covered – in botany,
invertebrate studies of the rocky intertidal zone
Feeding capacity – bait taken – for rats and mice –
index of density
Roadside counts – birds observed while driving
standard distances
31.
Population dispersionPopulation dispersion
patternspatterns
3 types
random
uniformclumped
32.
Population dispersion patterns
Random-when the position of each
individuals in a pop is independent of
the others
Uniform-it results as a form of some
negative interactions
Common among animal pop where
individuals defend an area for their own
exclusive use (territoriality) or in plant
pop where severe competition exist for
belowground resources, i.e water or
nutrients
33.
Population dispersion patternsPopulation dispersion patterns
Clumped-where individuals
occur in groups
Reason-suitable habitat or
resources may be distributed as
patches on a larger landscape
35.
Population growthPopulation growth
Refers to how the number of
individuals in a population increases or
decreases with time (N, t)
Reflects the difference between rates
of birth and death
in pop, if new births occur
in pop, if death occurs
36.
2 types of pop growth
Exponential population growth
dN = rmaxN
dt
Logistic population growth
dN = rmaxN (K-N)
dt K
Population
Growth
Mathematically
Defined
38.
Exponential GrowthExponential Growth
Continuous population growth in an unlimited
environment can be modeled exponentially.
dN / dt = rmax N
Appropriate for populations with overlapping
generations.
◦ As population size (N) increases, rate of population
increase (dN/dt) gets larger.
39.
Exponential GrowthExponential Growth
For an exponentially growing population, size
at any time can be calculated as:
Nt = Noert
Nt = number individuals at time t.
N0 = initial number of individuals.
e = base of natural logarithms.
r (= rmax ) = per capita rate of increase.
t = number of time intervals.
40.
PracticePractice
If the human population size in 1993 was
5.4 billion, what was the projected
population size in the year 2000?
r=0.0139
No = population size in 1993 = 5.4 billion
t = 7 years (year 2000 - 1993)
r = 0.0139
41.
Nt = No ert
Nt = (540,000,000) e(0.0139)(7)
Nt /540,000,000 = e 0.0973
Dust off your high school math skills. To get rid
of the exponent, simply take the (ln) of both
sides of the equation. Remember, when we
take the natural log of a quotient we end up
taking the ln of one value and subtracting it
from the ln of the other value (see below).
42.
ln (Nt /540,000,000) = ln (e 0.0973)
[here we're taking the natural log of the
quotient]
= ln(Nt) - ln(540,000,000) = 0.0973
[rewrite it as natural log of one value
minus natural log of the other value]
Nt = 595,000,000 or 5.95 billion
43.
Logistic Population GrowthLogistic Population Growth
As resources are depleted, population growth
rate slows and eventually stops: logistic population
growth.
◦ Sigmoid (S-shaped) population growth curve.
◦ Carrying capacity (K) is the number of individuals of a
population the environment can support.
Finite amount of resources can only support a finite number of
individuals.
44.
Logistic Population GrowthLogistic Population Growth
dN/dt = rmaxN(1-N/K)
rmax = Maximum per capita rate of increase under
ideal conditions.
When N nears K, the right side of the equation
nears zero.
◦ As population size increases, logistic growth rate
becomes a small fraction of growth rate.
Highest when N=K/2.
N/K = Environmental resistance.
45.
ProblemProblem
Suppose a population of butterflies is
growing according to the logistic
equation. If the carrying capacity is
500 butterflies and r = 0.1 individuals/
(individual*month), what is the
maximum possible growth rate for
the population?
46.
To solve this, you must first determine
N, population size. From the plot of dN/dt
vs. N, we know that the maximum
possible growth rate for a population
growing according to the logistic model
occurs when N = K/2, here N = 250
butterflies. Plugging this into the logistic
equation:
DN/dt = rN [1- (N/K)]
= 0.1(250)[1-(250/500)]
= 12.5 individuals / month
48.
Limits to Population GrowthLimits to Population Growth
Environment limits population growth by altering
birth and death rates.
Density-dependent factors
Disease, Parasites, Resource Competition
Populations do not show continuous geometric increase
When density increases other organisms reduces the fertility and
longevity of the individuals in the population
This reduces the rate of increase of the pop until eventually the pop
ceases to grow
The growth curve is defined as the sigmoid curve, S – shaped
K = carrying capacity (upper asymptote or maximum value) – the
maximum number of individuals that environment can support
Density-independent factors
Natural disasters
Climate
49.
r- and k-speciesr- and k-species
Characteristics of r- species
high biotic potential
Rapid development
Early reproduction
Single period reproduction per individual
Short lifecycle
Small body size
Regulated by the density-
independent factor
50.
Characteristics of k- species
low biotic potential
slow development
delayed reproduction
multiple period reproduction per individual
long lifecycle
large body size
Regulated by the density-dependent
factor
51.
Life history strategiesLife history strategies
K and r selection (MacArthur and Wilson 1967)
r-selected species
•r refers to the per capita rate of increase
•Selection favoring rapid growth
•Should be favored in new or disturbed
environments
•Less competition
K-selected species
•K refers to carrying capacity
•More prominent in species that are
typically at their carrying capacity
•Favors more efficient use of resources
•Live with competition
52.
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