1. Ecology
POPULATIONS

2. Objectives
Identify factors that describe, affect and limit population size.

3. The following standards will be addressed:

4. KEY CONCEPT Each population has a density, a dispersion, and a reproductive strategy.

5. What is a Population?
A population is a group
of the same species
living in the same place
at the same time.

6. Population density is the number of individuals that live in a defined area.
Population density is a measurement of the number of individuals living in a defined space.
Scientists can calculate population density.

7. Population dispersion refers to how a population is spread in an area.
Geographic dispersion of a population shows how individuals in a population are spaced.
Population dispersion refers to how a population is spread in an area.
Clumped
dispersion
Uniform
Random

8. There are three types of dispersion.
clumped

9. There are three types of dispersion.
uniform

10. There are three types of dispersion.
random

11. Survivorship curves help to describe the reproductive strategy of a species.
A survivorship curve is a diagram showing the number of surviving members over time from a measured set of births.

12. Survivorship curves can be type I, II or III.
Type I—low level of infant mortality and an older population
common to large mammals and humans
Type II—survivorship rate is equal at all stages of life
common to birds and reptiles
Type III—very high birth rate, very high infant mortality
common to invertebrates and plants

13. Objectives
Identify factors that limit population size.
Differentiate between density-dependent and density-independent factors.
Start of 14.4 notes

14. The following standards will be addressed:

15. KEY CONCEPT Populations grow in predictable patterns.

16. Changes in a population’s size are determined by immigration, births, emigration, and deaths.
The size of a population is always changing.
Four factors affect the size of a population.
immigration
births
emigration
deaths

17. Population Growth
Natural populations vary in size from year to year.
Three factors affect population size:
Number of births
The birth rate.
Number of deaths
The death rate.
Number of individuals entering/leaving
Immigration: movement into a population
Emigration: movement out of a population

18. Birth Rate > Death Rate: Population Grows
Population Growth
Birth Rate > Death Rate:
Population Grows
Birth Rate < Death Rate:
Population Declines
Birth Rate = Death Rate:
Population Steady

19. Population growth is based on available resources.
Exponential growth is a rapid population increase due to an abundance of resources.

20. Exponential Growth
If a population has abundant space and food, and is protected from predators and diseases, then the population will multiply and the size will increase.
Populations will exhibit exponential growth.
Shown via an exponential model.

21. Logistic Growth The Earth is NOT covered by unlimited organisms-Why?
There are not abundant resources.
When a population’s growth stops or slows following a period of exponential growth, it is now considered logistic growth (logistic model).

23. Carrying capacity is the maximum number of individuals in a population that the environment can support.
A population crash is a dramatic decline in the size of a population over a short period of time.

24. Ecological factors limit population growth.
A limiting factor is something that keeps the size of a population down.
There are two types:
density-dependent
density-independent

25. Density-dependent limiting factors are affected by the number of individuals in a given area.
predation
competition
parasitism and disease

27. Density-independent limiting factors limit a population’s growth regardless of the density.
unusual weather
natural disasters
human activities