1. Population Ecology
Ms. Day
AP Biology

2. Population Ecology
Population ecology = study of populations in an environment, including environmental influences on density and distribution, age structure, and population size
Population = group of same individuals of a single species living in the same general area at the same time and can interbreed

3. Density and Dispersion
Density is the number of individuals per unit area or volume
Dispersion/Distribution is the pattern of spacing among individuals within the boundaries of the population
Environmental and social factors influence spacing of individuals in a population

4. Measuring Density Population Density = individuals unit area
Unit area= length x width
Ex: What is the density of trees in 1 km2 in there are 1000 trees in 50 km2?
1000 trees = 20 trees
50 km km2

5. influenced by social interactions such as territoriality
Clumped distribution
influenced by resource availability (living in groups increases the effectiveness of hunting, spreads the work of protecting/caring for young)
most common
Uniform distribution
influenced by social interactions such as territoriality
Random distribution
the position of each individual is independent of other individuals

6. What kind of dispersion is this?

7. What kind of dispersion is this?

8. What kind of dispersion is this?

9. Measuring Population Density
You usually do NOT count organisms
Sampling techniques used by ecologists:
1. Quadrats (aka-Random sampling)
Count # of species
Repeat in several more
locations
Average results

10. Measuring Density
2. Indirect Counting- used for organisms that move around
Count # of nests, burrows or tracks

11. Measuring Density 3. Mark and Recapture Trap organisms
Mark with tags or dye
Capture again and count
Total Population = # in 1st capture x # in 2nd capture
# of marked animals recaptured

12. Study of theory and statistics behind population growth and decline
Demography
Study of theory and statistics behind population growth and decline
N = size of the population

13. Demographic Statistics
Birth rate (b)= number of offspring produced per time period
Death rate (d) or (m)= number of deaths per time period
Sex ratio = proportion of males and females in a population
Generation time = time needed for individuals to reach reproductive maturity

14. Demographic Statistics
These statistics together determine the size and growth rate of a given population
Population Growth =
(Births + immigration) - (deaths + emigration)
If birth rates are greater than death rates, population increases
If birth rates are less than than death rates, population decreases
If birth rates are equal to the death rates, population remains the same

15. Which age structure pyramid represents:
a developing country?
Future unemployment problems?
Adequate health care needs?

16. Population Growth and Size
Biotic potential = maximum growth rate of a population given unlimited resources/space, and lack of competition or predators
Rate varies from species to species
Carrying capacity (K)= maximum number of individuals that a population can sustain in a given environment without destroying the habitat

17. Limiting Factors Control Population Sizes
Density-dependent factors come into play when population approaches and/or passes the carrying capacity
Food supplies, waste, population- crowding diseases, H2O, mates, predators
Density-independent factors have nothing to do with the population size
THINK: NATURE
Floods, droughts, earthquakes, other natural disasters and weather conditions

18. Population Growth Ex: yeast, bacteria IN NATURE, NOT LIKELY…
Exponential Growth =
population grows as if there are no limitations to how large it can get (biotic potential)
J-curve
A population increases slowly at first (the "lag phase") and then grows increasingly rapidly with time ("log phase”)
IN NATURE, NOT LIKELY…
Ex: yeast, bacteria

19. Population Growth (con’t)
2. Logistic Growth = population growth slows to zero and population size tends to stabilize because of environmental resistance (Limiting factors)
S-curve
Set by carrying capacity
Ex: HUMAN POPULATION, ELEPHANTS K

20. Point of Maximum growth (K/2)

21. 2 types of population growth
Number of generations
Population size (N)
K = 1,500
1,500
2,000
1,000
500 15 10 5
Logistic growth
Exponential
growth
= 1.0N dN dt
1,500 – N

22. 2 Categories of Organismal Growth
Organisms can belong to…
K-selected populations: a roughly constant size whose members have low reproductive rates. (THINK: “K”onstant growth and “K”are)
Offspring require extensive postnatal care
Produce few LARGE offspring
Long maturation time
Long lifespan/low death rate
Usually reproduce often throughout lifetime (occurs later in life)
Density dependent factors often limit growth
Logistic growth pattern
Ex: humans, elephants, monkeys
HANG ON!!

23. Or organisms can belong to…
r-selected populations experience rapid growth (THINK: really fast growth)
Offspring are small
Produce large #’s of offspring
Offspring mature rapidly
Offspring require little postnatal care
Short lifespan/high death rate
Usually reproduce once throughout lifetime (occurs early in life)
Density independent factors often limit growth
Exponential growth pattern
Ex: bacteria, mice, lizards

24. Which surviorship curve shows:
An r- strategist? Why?
An k- strategist? Why?

25. Predator-Prey Cycling- Population BOOMS and BUSTS!
Many populations undergo boom-and- bust cycles
Boom-and-bust cycles are influenced by complex interactions between biotic and abiotic factors