2.6 Changes:
Population Dynamics
Assessment Statements
2.6.1 Explain the concepts of limiting factors and
carrying capacity in the context of population
growth.
2.6.2 Describe and explain S- and J- population
curves.
2.6.3 Describe the role of density-dependent and
density-independent factors, and internal and
external factors, in the regulation of populations.
2.6.4 Describe the principles associated with
survivorship curves including, K- and r-strategists.
Population Dynamics
 Changes in population size and the factors
that regulate populations over time.
Population Density
 The number of individuals per unit area/volume.
 Example: The number of oak trees per km2 in
a forest.
Estimation of Population Size
1. Individual counts (not always practical)
2. Transects or Quadrats
3. Mark-recapture method: Lincoln Index
N= marked individual X total catch second time
recaptured marked individuals
Example: pond turtles
1992: 18
1993: 34 (12)
1994: 30 (18)
Estimation of Population Size
Example: pond turtles
1992: 18
1993: 34 (12)
1994: 30 (18)
1992-93: N = 18(34) = 51 turtles
12
_________________________________________
1993-94: N = 34(30) = 56.7 turtles
18
_________________________________________
So: 51 + 56.7 = 107.7 = 53.9 turtle estimation
2
Dispersion
 The distribution of individuals within
geographical population boundaries.
 Three examples of dispersion patterns:
1.
Clumped
2.
Uniform
3.
Random
Dispersion Patterns
1. Clumped
a.
individuals are aggregated in patches
b.
unequal distribution of resources in the
environment.
Example: trees around a lake or pond
Dispersion Patterns
 2.
Uniform
a.
individuals are evenly distributed
b.
interactions among individuals of a
population
Example: creosote bushes in the desert
Dispersion Patterns
 3.
Random
a.
unevenly distributed
b.
random dispersion is rare
Example: clams in a mud flat
Understanding Population Growth
1.
Exponential Growth Model
Exponential growth: The rate of expansion (growth) of a
population under ideal conditions.
Exponential Growth – J Curve
 Example: bacteria
produces a J-shaped
curve
Number of
individuals
(N)
Time
Understanding Population Growth
2. Logistic Growth Model
logistic growth: environmental factors that restrict the growth
of a population
(called: population limiting factors)
K: Carrying Capacity
 The maximum stable population size that a
particular environment can support over a
relatively long period of time (K).
Logistic Growth: S-Curve
 Example: turtles in a pond
K
produces a S-shaped
curve
Number of
individuals
(N)
Time
Draw an s-curve and draw
a j-curve
 Label each
Question
 What if?
 N, the number of individuals = almost 0:
exponential growth
 N, the number of individuals = almost K
(carrying capacity):
growth rate is approaching zero
Zero Population Growth
Factors That Limit Population
Growth
1. Density-Dependent Factors:
 Population-limiting factors whose effects
depend on population density.
 The greater the pop, the greater the effects.
(negative feedback)
Examples:
1. Limited food supply
(competition)
2. Disease
3. Predation/parasitism
4. War
Factors That Limit Population
Growth
2. Density-Independent Factors:
 Population-limiting factors (abiotic) whose
occurrence is not affected by pop density.
 Increases death rate & decreases birth rate
 Affects depend on severity of the event
Examples: 1.
2.
3.
4.
Earthquakes
Fires
Hurricanes
Freeze in the fall
Boom and Bust Species
 A rapid increase (boom) in a population
followed by a sharp decline (bust).
 Examples:
a. Daphnia in a pond
number of
individuals
in pop.
boom
Time
bust
Boom and Bust Species
 Sometimes species (carnivore) depend on
other species (prey) for food.
 Example: Snowshoe hare and lynx
number of
individuals
in pop.
Years
Survivorship Curves
 Life History:
Series of events from birth through reproduction to
death.
 Two basic types of life history strategies:
1. Opportunistic life history
(r-strategist species)
2. Equilibrial life history – limited by carrying
capacity(K)
(K-Strategist species)
Opportunistic life history
(r-strategist species)
Characteristics:
1.
2.
3.
4.
5.
6.
7.
8.
maturing time:
life span:
mortality rate:
times female is reproductive:
age at first reproduction:
size of offspring:
parental care:
Size of organism:
short
short
often high
usually once
early
small
none
small
Equilibrial life history
(K-strategist species)
Characteristics:
1. maturing time:
long
2. life span:
long
3. mortality rate:
often low
4. times female is reproductive:
often many
5. age at first reproduction:
late
6. size of offspring:
large
7. parental care:
often extensive
8. Size of organism:
tend to be large
Life History Examples
R-strategist species:
1.
Garden weeds
2.
Insects
3.
Desert flowers
K-strategist species:
1.
Humans
2.
Apes
3.
Elephants
Survivorship Curves
 Type 1 survivorship curve:
High survival rates until old age.
K or r strategist?
K
Example?
% of
survivors
humans
% of maximum life span
Survivorship Curves
 Type 3 survivorship curve:
High mortality rates as young but
decreased mortality at later ages.
K or r strategist?
r
% of
survivors
Examples?
% of maximum life span
turtles
oysters
frogs
insects
Survivorship Curves
 Type 2 survivorship curve:
Intermediate between the extremes.
Example
squirrel
% of
survivors
% of maximum life span
Human Population Growth
 Age structure
Proportions of individuals of a population in
different age groups.
A typical population has three main age groups
(age structure).
1.
Pre-reproductive (youth)
2.
Reproductive
3.
Post-reproductive
Age Structure
Post-reproductive
Reproductive
Pre-reproductive
Human Population Growth Today
 Human population as a whole is growing
exponentially.
 Has doubled (doubling-time) three times in the
last three centuries (doubled the carrying
capacity several times).
 Is now 7 billion, might reach ~8 billion by 2020.
http://www.worldometers.info/wo
rld-population/
Question:
 What are the reasons for the increase in human
population?
 Answer:
1.
Improved health
2.
Technology
3.
Decreased death rates
Question:
 What is Zero Population Growth (ZPG)?
 Answer:
a.
birth rate equals death rate.
b.
intrinsic growth (r) = 0
Question:
 What are two ways the human population
can reach Zero Population Growth?
1.
Limit the # of offspring per couple
a. Reduces family size
b. Voluntary contraception
c. Family planning
2.
Delay reproduction
(late 20’s instead of early 20’s)
Question:
 What will happen to human’s if the
population continues to grow at this rate?
 Is there a limit to human population
growth? Why/why not?
 What EVS does your argument support?
Explain