1. Population ecology
Chapter 53- AP Biology

2. Population Ecology
The study of populations in relation to their environment
Explores how biotic and abiotic factors influence the density, distribution, size and age structure of populations
What is a population?

3. Density and Dispersion
Density: number of individuals per unit area or volume
Ex: number of oak trees per square kilometer in the Minnesota country
Dispersion:
Random
Clumped- most common pattern of dispersion (plants, fungi)
Uniform – often seen with territoriality

4. Population Density is DYNAMIC

5. Guess the dispersion Pattern….
Calculate Density of….
5 moose in a township (24,000 square miles)
10,000 Oak trees in 25 square miles
Guess the dispersion Pattern….

6. Demographics
Demography: study of the vital statistics of populations and how they change over time
Life Tables (Usually follow certain “cohorts”): death rate, birthrate, etc.
Survivorship curves
Reproductive Rates

7. Life Table: “age specific summaries of survival pattern of a population”

8. Survivorship Curves
Type I: few offspring but provided with good care; low infant death rate
Type II: Intermediate; death rate remains constant over time
Type III: many offspring with a high infant mortality; fish, oysters, etc.

9. Reproductive Table

10. Natural Selection & Life History
Natural selection favors traits that improve an organism’s chances of survival and reproductive success.
“Life history traits are evolutionary outcomes reflected in their development, physiology, and behavior”
Semelparity: “beget once,” organism produces once in its lifetime (salmon, agave)
Iteroparity: “repeted,” reproducing many times in a lifetime (humans, dogs)
Two critical factors
Survival rate of the offspring
Likelihood that the adult will survive to reproduce once again

11. Exponential Growth Population Births Deaths during a = and - and
time interval        immigrants emigrants
simplified:    Δ N/ Δ t  = B-D

12. Per capita rate of increase
“Average births or deaths per unit of time in average population”
Example: 34 births per year in a population of 1,000 (or 34/1,000)
annual per capita birth rate  b = .034
50 deaths per year in a population of 1,000
annual per capita death rate  d = .05
In the equation Δ N/ Δ t  = B-D
B = bN and D = dN

13. Rate of Increase (r) if (r > 0 ), then population is growing
r = b – d
if (r > 0 ), then population is growing
if (r < 0 ), then population is declining
Zero growth population (ZGP) is when r = 0

14. Revised equation
Δ N/ Δ t  = rN

15. Exponential growth Δ N/ Δ t = rmaxN
Under “perfect conditions,” with abundant resources, a population will grow “without limit”
Δ N/ Δ t  = rmaxN
Result is a “J” curve
Greater ( r) means faster growth

16. African elephant, Kruger National Park, South Africa
Grew exponentially for 60 years when they were first protected from hunting

17. Practice
In 2006, the United States had a population of about 300 million people. If there were 14 births and 8 deaths per 1,000 people, what was the country’s net population growth that year (ignoring immigration and emigration)?

18. Practice
In 2006, the United States had a population of about 300 million people. If there were 14 births and 8 deaths per 1,000 people, what was the country’s net population growth that year (ignoring immigration and emigration)?
14/1000 = .014 = annual per capita birth rate  b
8/1000 = .008 = annual per capita death rate  d
b – d = .006 annual per capita growth rate
.006 x 300 million = 1,800,000 net growth in 1 year

19. Logistical Growth- The “real world”
Carrying Capacity (k): the maximum population size that a particular environment can sustain
Varies over time
Depends on limiting factors
Result = change in r
Logistic growth: per capita rate of increase (r ) approaches zero as carrying capacity (k) is reached

20. Logistic Growth
“as N increases, r decreases”

21. Example of Logistic growth in Lab

22. Life History Trait Selection
k-selection: density-dependent selection, select for traits that are sensitive to population density; (when organisms are near carrying capacity).
r-selection: density-independent selection, select traits that maximize reproductive success at LOW densities

23. Question
When a farmer abandons his field, it is quickly colonized by rapidly-growing weeds. Is this a k-selected or r-selected species?

24. Density and population growth
Density-dependent: trait or growth rate that is affected by population density
Ex: death rate may rise due to overpopulation
Density-independent: trait or growth rate that is NOT affected by population density
Ex: death rate may rise due to forest fires

25. Density-Dependent population regulation
Competition
Territoriality
Disease
Predation
Toxic wastes
Intrinsic factors (stress  hormones)

26. Population dynamics
Complex interactions between biotic and abiotic factors that cause variation in the size of populations

27. Human Populations

28. Trends ZGP (Stable population)
High birth rate – high death rate OR
Low birth rate – low death rate
Demographic transition = movement towards low birth rate and low death rate
Sanitation
Better Health Care
Improved Education access

29. Age Structure
Relative number of individuals of each age group in a population

30. Infant mortality and life expectancy

31. Global Carrying capacity? . .
Estimated at 7.8 – 10.8 billion
Ecological footprint: sum of aggregate land and water area required by each person, city, or nation to produce all the resources it consumes and absorb all the waste it generates.

32. You should be able to…
Find the density and dispersion of a given species
Interpret life tables, survivorship curves, and age structure tables
Identify and describe “r” strategists and “k” strategists
Interpret logistic and exponential population growth models
Identify and describe density-dependent and density-independent factors