1. POPULATION GROWTH & MEASUREMENT
AP Environmental Science
Chapter 6

2. WHAT IS A POPULATION?
A group of interbreeding individuals within a geographical location.
POPULATION SIZE is determined by:
#of births (based on fertility rates)
# of deaths
# of indiv that
enter or leave the population

3. Population Graphs measure status of populations
J-curve or Exponential Growth Curve
S-Curve or Logistics Curve

4. POPULATION DENSITY
DENSITY: number of individuals per unit area or volume
Ex: Suppose there are
150 bullfrogs living in a
pond that covers an
area 3 square km.
What is the population density?

5. Population density Population Density =
Number of Individuals (150 frogs)
Unit Area (3 sq KM)
= 50 bullfrogs per square kilometer!

6. Populations Dynamics Population Modeling

7. CARRYING CAPACITY Max population that a habitat can supportE D A T O S F O D D I S E A D I S A s T E R =
Max population that a habitat can support
(Level line)

8. Carrying Capacity Factors
These limiting pressures keep a population in check such as carrying capacity:
1. # of Predators
2. Amount of Food & Water Resources
Disease
Natural Disasters
Reproductive ability

9. Other factors – H I P P O can decrease in population!!
H=Habitat
I= Invasive species
P= Pollution
P=Other interacting populations
O=Overconsumption

10. Exponential Increase (J-curve)
In a J-curve, the popul keeps growing quickly (exponentially over time).

11. What causes J-curve to occur?
Conditions:
No enemies
No competition.
Plenty of food & water
4. Low % of disease
J-curve is usually a temporary situation=Population crash.

12. Exponential Growth Math Model
Change in N
Change in time
Initial Population
Rate of reproduction
Time

13. dN/dt = rN Time (dt) N (dN) Rate (r)* r x N
Exponentially how does it look for a
J-curve T1 2 10
10x2 = 20
2x10 T2 20
10x20=200
2x10x10 T3
200
10x200=2,000
2x10x10x10
2000
10x2,000=20,000
2x10x10x10x10 T4
20,000
10x20,000=200,000
2x10x10x10x10x10
N=2 cockroaches (male and female)
r= 2 cockroaches can produce 20 offspring in 3 months
a. The rate of growth (r) 20/2 adults or 10 per 1 adult.
b. The growth rate (r) equals 10

14. Figure 06_03

15. Exponential Growth can Crash
When population can no longer sustain itself without food resources, pop decrease beneath the carrying capacity.

16. Population Crash Isle Royale, Michigan National Park Moose pop
quickly in
Wolf pop due to
Parvovirus passed on from domesticated dogs visiting the National Park.
Moose population
Due to tick infestation.

17. S-curve (Logistics curve)

18. S-curve or Logistics Population
1. Population at equilibrium.
S-curve may change (increase & decrease) slightly, but is constant near the carrying capacity.
May be considered “restricted growth”.

19. Factors that keep populations within carrying capacity
Migration

20. Logistics Curve Model dN = rN 1-N dt K
dN = change of population over time dt
N = Population
K= Current Carrying Capacity
r= rate of change or reproductive rate of a speciesd

21. Logisitics/Carrying Capacity Connection
If the carrying capacity (K) = 100 wolves
If the N = 100 wolves (wolves bred successfully to increase population)
Look at the 1-N/K part:
100
1- 1 = 0
dN/dt = rN(0)=0!!!

22. Logistics & CC (continued)
There is no change in dN/dt-no population growth! What if N=50? Plug it into 1-N/K to see how it affects the reproductive rate for a population. 1-50/100 = 1-1/2 = 1/2rN or half of the maximum reproductive rate for the wolves.

23. Logistics & CC (continued)
If N = 10…plug into 1-N/K
(1- 10) = (1-.10) = .90
100
dN = rN(.90) or dN is at a rate of
dt dt
90% as fast as the max possible reproductive rate for the wolves!

24. Lincoln Peterson Population Estimate Model
Estimating population size by random sampling an ecosystem.
Focus on population density or animal abundance.
Model: n1 = m2 OR N= n1 x n2
N n m2
n1=#animal marked & released 1st time
n2=# animals captured during 2nd session
m2-# animals captured during 2nd session & are marked.
Est Population

25. Population Measurement in Review
J-curve
Exponential Curve
S-curve
Logistics Curve
Carrying Capacity

26. Population Equilibrium
Equilibrium: the balance between births and deaths within a population

27. Other Population Considerations
Environmental Resistance
Population Dispersal
Reproductive Potential

28. Environmental Resistance
Factors/pressures that limit a population’s ability to increase (CC)
Density Dependent
Density Independent
Parasites
Temperature
Disease
Moisture, light, pH salinity
Competitors
Weather
Predators
Natural Disasters
Human Intervention
Lack of habitat/territory

29. Population Dispersal Definition
Different patterns of how a species or population will inhabit a certain geographical location.

30. Population Dispersal is determined by:
Random
Uniform
Clumped

31. POPULATION DISPERSAL A. RANDOM: 1. Least Common
2. Found anywhere in envir.
3. High mobility such as wind blown
Ex: Dandelions

32. POP DISPERSAL B. Uniform
Rare Occurrence but does occur in nature! (Hawks, wolves)
Can indicate human impact
a. Plantations, orchards, etc.

33. UNIFORM POPULATION DISP.
Red-Tailed Hawk
Orchards

34. CLUMPED POP DISPERSAL C. CLUMPED: Patchy, most common
Protection, avail of natural resources, to survive
Ex: Allelopathy, fish, plants, trees, etc.

35. Clumped Dispersal – Purple Loosestrife Patterns in US

36. Reproductive Potential
…Is an organism’s ability to grow at the fastest rate.
(To replenish the species—innate!)

37. REPRODUCTIVE POTENTIAL COMPARISON
R-selected
Hint: Rapid Repro
Early reproduction
Short life span
Hi mortality
Little/no parental care
Large # of offspring produced
Inhabit lower trophic levels (1st order consumers)
2. K-selected
Hint: Longer Repro
Late reproduction
Long life span
Low mortality
High parental care
Small # of offspring produced

38. REPRODUCTION TYPES
K-SELECTED TYPE
R-SELECTED TYPES

39. Reproductive potential – “R”
Bacterium can produce 19 million descendants in a few days!!
Mosquitoes live days laying eggs every 3 days.
Mosquito rafts have eggs;. hatch in 48 hours

40. Reproductive potential – “K”
Some species have higher reproductive potential!!
K-Potential Gestation
Times:
Human= 9 months
Elephants= 22 months
Oppossum = days (marsupial)

41. CRITICAL NUMBERS
Survival & recovery of population depends on a minimum population base—its critical number.

42. Factors Affecting Critical Number
C1. IMMIGRATION: movement of indiv into an area C2. EMIGRATION: movement of individuals which leave an area. Plus Environmental Resistance Factors

43. Critical Numbers
If pop falls below critical number, breeding may fail and extinction could occur.
Threatened: species whose pops are declining rapidly
Endangered: near critical number and may become extinct.