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Population Dynamics

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The number of individuals per unit area volume. ... Example: creosote bushes in the desert. Dispersion Patterns. 3. Random. a. unevenly distributed ... – PowerPoint PPT presentation

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Title: Population Dynamics


1
PopulationDynamics
2
Population Dynamics
  • Changes in population size and the factors that
    regulate populations over time.

3
Population Density
  • The number of individuals per unit area volume.
  • Example The number of oak trees per km2 in a
    forest.

4
Estimation of Population Size
  • 1. Individual counts (not always practical)
  • 2. Transects
  • 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)

5
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

6
Dispersion
  • The distribution of individuals within
    geographical population boundaries.
  • Three examples of dispersion patterns
  • 1. Clumped
  • 2. Uniform
  • 3. Random

7
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

8
Dispersion Patterns
  • 2. Uniform
  • a. individuals are evenly distributed
  • b. interactions among individuals of a
    population
  • Example creosote bushes in the desert

9
Dispersion Patterns
  • 3. Random
  • a. unevenly distributed
  • b. random dispersion is rare
  • Example clams in a mud flat

10
Understanding Population Growth
  • Exponential Growth Model
  • Exponential growth The rate of expansion
    (growth) of a population under ideal conditions.

11
Exponential Growth
  • Example bacteria

produces a J-shaped curve
12
Understanding Population Growth
  • 2. Logistic Growth Model
  • logistic growth environmental factors that
    restrict the growth of a population
  • (called population limiting factors)

13
K Carrying Capacity
  • The maximum stable population size that a
    particular environment can support over a
    relatively long period of time (K).

14
Logistic Growth
  • Example turtles in a pond

K
produces a S-shaped curve
15
Draw an s-curve and draw a j-curve
  • Label each

16
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

17
Factors That Limit Population Growth
  • 1. Density-Dependent Factors
  • a. Population-limiting factors whose effects
    depend on population density.
  • b. The greater the pop, the greater the effects.
  • Examples 1. Limited food supply
  • 2. Plagues
  • 3. Predation
  • 4. War

18
Factors That Limit Population Growth
  • 2. Density-Independent Factors
  • a. Population-limiting factors (abiotic) whose
    occurrence is not affected by pop density.
  • b. the greater the pop, the greater the effects
  • Examples 1. Earthquakes
  • 2. Fires
  • 3. Hurricanes
  • 4. Freeze in the fall

19
Boom and Bust Species
  • A rapid increase (boom) in a population followed
    by a sharp decline (bust).
  • Examples
  • a. Daphnia in a pond

boom
bust
20
Boom and Bust Species
  • Sometimes species (carnivore) depend on other
    species (prey) for food.
  • Example Snowshoe hare and lynx

21
Evolution Shapes Life Histories
  • Life History
  • Series of events from birth through reproduction
    to death.
  • Two basic types of life history strategies
  • 1. Opportunistic life history
  • (r-selected species)
  • 2. Equilibrial life history
  • (K-selected species)

22
1. Opportunistic life history(r-selected species)
  • Characteristics
  • 1. maturing time short
  • 2. life span short
  • 3. mortality rate often high
  • 4. times female is reproductive usually once
  • 5. age at first reproduction early
  • 6. size of offspring small
  • 7. parental care none
  • 8. Size of organism small

23
2. Equilibrial life history(K-selected 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

24
Life History Examples
  • r-selected species
  • 1. Garden weeds
  • 2. Insects
  • 3. Desert flowers
  • K-selected species
  • 1. Humans
  • 2. Apes
  • 3. Elephants

25
Survivorship Curves
  • Type 1 survivorship curve
  • High survival rates until old age.
  • Example

humans
26
Survivorship Curves
  • Type 2 survivorship curve
  • Intermediate between the extremes.
  • Example

squirrel
27
Survivorship Curves
  • Type 3 survivorship curve
  • High mortality rates as larvae but decreased
    mortality at later ages.
  • Example

oysters frogs insects
28
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
  • 2. Reproductive
  • 3. Post-reproductive

29
Age Structure
30
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 6.5 billion, might reach 8 billion by
    2020.

31
Question
  • What are the reasons for the increase in human
    population?
  • Answer
  • 1. Improved health
  • 2. Technology
  • 3. Decreased death rates

32
Question
  • What is Zero Population Growth (ZPG)?
  • Answer
  • a. birth rate equals death rate.
  • b. intrinsic growth (r) 0

33
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 20s instead of early 20s)
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