1. Population Ecology

2. Populations
A population is a group of individuals of the same species that live in the same area

3. Population Ecology: Vocabulary
Density:
The number of individuals per unit area/volume
Example: 47 elephants/km2
Dispersion:
The pattern of spacing among individuals in a population
Clumped
Uniform
Random

5. Uniform Environmental conditions are uniform
Causes COMPETITION or antagonism between organisms

6. Clumping Most common Reproductive patterns favor clumping
Social behaviors lead to clumping
Optimal density is usually intermediate (medium)

7. Random No competition No tendency to group/clump
Conditions are uniform
Rarely happens!

8. Factors That Influence Population Size
There are 3 major factors that influence population size:
1. the number of births
2. the number of deaths
3. the number of individuals that enter or
leave a population
- immigration:
individuals entering an existing population
- emigration:
individuals leaving an existing population

9. Reproductive Episodes
Clutch size:
Number of offspring produced at each reproductive episode
Semelparity
A life history in which an organism spends most of its energy in growth and development, expend their energy in one large reproductive effort, and then die
Many insects, annual plants, salmon, etc.

10. Reproductive Episodes
Iteroparity
A life history pattern in which organisms produce fewer offspring at a time over a span of many seasons
Example: humans, panda bears, etc.

11. Estimating Population Size
The mark-recapture method can be used to estimate the size of a population
Capture, mark, release
Recapture and count
Equation:
N = Number marked x Total catch 2nd time
Number of marked recaptures

12. Patterns of Population Growth
Exponential Growth:
Occurs in ideal conditions with unlimited resources
J shaped curve
Book example:
1 bacterium (reproducing every 20 minutes) could produce enough bacteria to form a 1-foot layer over the entire surface of the Earth in a day

13. Patterns of Population Growth
Exponential growth cannot continue indefinitely
It is characteristic of populations who are entering a new environment OR those whose numbers are rebounding from a catastrophic events

14. r- strategists
Grow exponentially when environmental conditions allow; when conditions worsen, population size plummets.
Short life span
Reproduce early in life
Many offspring/large clutch size
Usually small in size
Little or no parental care
Bacteria, some plants, insects

15. Patterns of Population Growth
Logistic Growth:
Pattern of population growth which takes into account the effect of population density on population growth
Occurs when resources become more scarce
Characterized by an S-shaped curve

16. Patterns of Population Growth
Carrying capacity (K):
The maximum number of individuals that a particular environment can support over a long period of time
Determined by such limiting factors as crowding and food resources
Graph levels off at carrying capacity
K-selected populations (equilibrial populations) live near or at the carrying capacity

17. K-strategists Density stays near carrying capacity.
Large, slow growing organisms
Small population sizes
Long life span; slow maturation
Few young/small clutch size
Reproduce late in life
Parental care
Most large mammals; endangered species

18. Carrying Capacity

19. Boom-and-Bust Cycles

20. Limiting Factors
There are a number of factors that limit the size of populations:
Density-dependent limiting factors
Density-independent limiting factors

21. Density-Dependent Limiting Factors
The effect of density-dependent limiting factors intensifies as the population increases
Intraspecific competition
Food, space, etc.
Predation
Disease (if caused by pathogen/contagious)

22. Density-Independent Limiting Factors
The occurrence and severity of density-independent limiting factors are unrelated to population size
Climate
Disease (if not caused by pathogen/not contagious)
Pollution

23. The Interaction of Limiting Factors
Density-dependent and density-independent limiting factors often work together to regulate the size of a population
Deer in snowy winter
Starve from lack of food (DDLF)
Severity of winter/depth of snow determines access to food (DILF)

24. Survivorship Curves Type I- live to old age & die (most large mammals)
Type II- constant mortality rate (rodents, lizards, hydra)
Type III- high mortality at young age, but if they survive they live a long life.

25. Age-Structure Diagrams

26. Human Population Growth

27. Human Population Growth
The human population has been increasing exponentially since approximately 1650

28. Human Population Growth
Implications of exponential human population growth:
Lack of food supplies
Lack of space
Lack of natural resources (metals, fossil fuels, etc)
Lack of sites for waste disposal
Ecologists cannot agree on a carrying capacity for Earth
Are we going to reach carrying capacity through individual choices and/or government programs? OR
Is Earth’s population going to “level off” as a result of mass deaths?