organism
population
community
ecosystem
biosphere
Population Ecology
AP Biology
Life takes place in populations
 Population

group of individuals of same species in
same area at same time
 rely on same
resources
 interact
 interbreed
AP Biology Ecology: What factors affect a population?
Population
Why Population Ecology?
 Scientific goal

understanding the factors that influence the
size of populations
 general principles
 specific cases
 Practical goal

management of populations
 increase population size
 endangered species
 decrease population size
 pests
 maintain population size
 fisheries management

AP Biology
maintain & maximize sustained yield
Factors that affect Population Size
 Abiotic factors



sunlight & temperature
precipitation / water
soil / nutrients
 Biotic factors

other living organisms
 prey (food)
 competitors
 predators, parasites,
disease
 Intrinsic factors

AP Biology
adaptations
At risk populations
 Endangered species

limitations to range / habitat
 places species at risk
Devil’s hole
pupfish
Iiwi
Hawaiian
bird
Socorro
isopod
Iriomote cat
New Guinea
tree
kangaroo
Catalina
Island
mahogany
tree
AP Biology
Northern white rhinoceros
Population Spacing
 Dispersal patterns within a population
Provides insight into the
environmental associations
& social interactions of
individuals in population
clumped
random
AP Biology
uniform
Clumped Pattern
AP Biology
(most common)
Uniform
May result from
direct
interactions
Clumped
patterns
between individuals
in the population
 territoriality
AP Biology
Population Size
 Changes to
population size

adding & removing
individuals from a
population
 birth
 death
 immigration
 emigration
AP Biology
Population growth rates
 Factors affecting population growth rate

sex ratio
 how many females vs. males?

generation time
 at what age do females reproduce?

age structure
 how females at reproductive age in cohort?
AP Biology
Survivorship curves
 Graphic representation of life table
The relatively straight lines of the plots indicate relatively constant
rates of death; however, males have a lower survival rate overall
than females.
Belding ground squirrel
AP Biology
Age structure
 Relative number of individuals of each age
What do these data imply about population growth
in these countries?
AP Biology
Survivorship curves
 Generalized strategies
Survival per thousand
1000
Human
(type I)
Hydra
(type II)
What do these graphs
tell about survival &
strategy of a species?
I. High death rate in
post-reproductive
years
100
II. Constant mortality
rate throughout life
span
Oyster
(type III)
10
1
0
25
50
75
Percent of maximum life span
AP Biology
100
III. Very high early
mortality but the
few survivors then
live long (stay
reproductive)
Reproductive strategies
 K-selected



late reproduction
few offspring
invest a lot in raising offspring
 primates
 coconut
 r-selected



K-selected
early reproduction
many offspring
little parental care
 insects
 many plants
AP Biology
r-selected
Trade offs
Number & size of offspring
vs.
Survival of offspring or parent
r-selected
K-selected
“Of course, long before you mature,
AP Biology
most of you will be eaten.”
Life strategies & survivorship curves
K-selection
Survival per thousand
1000
Human
(type I)
Hydra
(type II)
100
Oyster
(type III)
10
r-selection
1
0
25
50
75
Percent of maximum life span
AP Biology
100
Exponential growth rate
 Characteristic of populations without
limiting factors

introduced to a new environment or rebounding
from a catastrophe
Whooping crane
coming back from near extinction
AP Biology
African elephant
protected from hunting
Regulation of population size
marking territory
= competition
 Limiting factors

density dependent
 competition: food, mates,
nesting sites
 predators, parasites,
pathogens

density independent
 abiotic factors
 sunlight (energy)
 temperature
 rainfall
APcompetition
Biology
for nesting sites
swarming locusts
Introduced species
 Non-native species


transplanted populations grow
exponentially in new area
out-compete native species
 loss of natural controls
 lack of predators, parasites,
competitors


reduce diversity
examples
 African honeybee gypsy moth
 gypsy moth
 zebra mussel
 purple loosestrife
AP Biology
kudzu
Zebra mussel
~2 months


AP Biology
ecological & economic damage

reduces diversity
loss of food & nesting sites
for animals
economic damage
Purple loosestrife
1968
1978


AP Biology
reduces diversity
loss of food & nesting sites
for animals
Logistic rate of growth
 Can populations continue to grow
exponentially? Of course not!
no natural controls
K=
carrying
capacity
What happens as
N approaches K?
AP Biology
effect of
natural controls

varies with
changes in
resources
What’s going
on with the
plankton?
AP Biology
10
8
6
4
2
0
1915
1925
1935
1945
Time (years)
Number of cladocerans
(per 200 ml)
population size
that environment
can support with
no degradation
of habitat
Number of breeding male
fur seals (thousands)
Carrying capacity
 Maximum
500
400
300
200
100
0
0
10
20
30
40
Time (days)
50
60
Changes in Carrying Capacity
 Population cycles

predator – prey
interactions
At what
population level is the
carrying capacity?
K
K
AP Biology
Population of…
China: 1.3 billion
India: 1.1 billion
Human population growth
Doubling times
250m  500m = ?
500m  1b = ?
1b  2b = 80y (1850–1930)
2b  4b = 75y (1930–1975)
What factors have contributed to
this exponential growth pattern?
Is the human
population reaching
carrying capacity?
adding 82 million/year
~ 200,000 per day!
20056 billion
Significant advances
in medicine through
science and technology
Industrial Revolution
Bubonic plague "Black Death"
1650500 million
AP Biology
Distribution of population growth
World population in billions
11
uneven distribution
of population:
10 are in developing countries
90% of births
9
uneven distribution of resources:
8 consumes ~90%
wealthiest 20%
of resources
There
are choices as
increasing gap
poor
which future path
7 between rich & to
6
5
4
3
the world takes…
World total
the effect of income
What is K
& education
for humans?
10-15 billion?
Developing countries
2
1
0
1900
AP Biology
Developed countries
1950
Time
2000
2050
Measuring population density
 How do we measure how many
individuals in a population?
number of individuals in an area
 mark & recapture methods

Difficult to count a moving target
AP Biology
sampling populations
Population Ecology Practice!
1. Uniform spacing patterns in some
bushes are most often associated with
a.
b.
c.
d.
e.
AP Biology
chance
patterns of high humidity
the random distribution of seeds
competitive interactions among
individuals in the population
the concentration of nutrients within
the population’s range
Which of the following is a
conclusion that can be
drawn from this graph?
a. There appears to be a negative
correlation between brood
enlargements and parental survival.
b. Male survivability decreased by 50% between reduced and
enlarged brood treatments
c. Female survivability is more negatively affected by larger brood
size than is male survivability
d. Both males and females had increases in daily hunting with the
enlarged brood size
e. Chicks in reduced brood treatment received more food, weight
gain, and reduced mortality
AP Biology
 A population of ground squirrels has an annual
per capita birth rate of 0.06 and an annual per
capita death rate of 0.02. Estimate the number of
individuals added to (or lost from) a population of
1,000 individuals in one year
a.
b.
c.
d.
e.
40 individuals added
120 individuals added
20 individuals lost
400 individuals added
20 individuals added
AP Biology