Population Ecology Notes

HS Biology Notes

1. Population Ecology

2. What is Population? A group of the same species that lives in one area

3. 5 Characteristics of Population Geographic Distribution Density Dispersion Growth Rate Age Structure

4. Geographic Distribution The range of the population Describes the area that is inhabited by the population Such as: The mold on a piece of bread The migration area of whales

5. Population Density The number of individuals per unit area # of individuals Area (units 2 ) Variation in density depends on: The species The ecosystem = population density

6. Practice Problem If scientists sampling a population of deer counted 200 individuals in an area of 10 square kilometers, what is the density of this deer population per square kilometer? A: 20 deer per square kilometer

7. 2000 U.S. population density in persons per sq. mile (contiguous U.S. only). Averaged on a per-county basis. Legend, light to dark (white to dark blue): 0-1 (white) 1-4 (yellow) 5-9 (yellow-green) 10-24 (green) 25-49 (teal) 50-99 (dark teal) 100-249 (blue) 250-66,995 (violet)

8. Dispersion The spatial distribution of individuals within the population Three types: Clumped Dispersion Even Dispersion Random Dispersion

9. Clumped Dispersion Individuals are clustered together Occurs: When resources (food, water, living spaces) are clumped together Species have a certain social behavior For example: herding animals, flocks of birds, schools of fish, hives of bees

10. Even Dispersion ( a.k.a Uniform Dispersion) Individuals are separated by a fairly even distance. Occurs: As a result of social interaction Individuals trying to get as far away from each other as possible. Limited resources, competition, nesting

11. Random Dispersion Location of one individual is independent of the location of the other individuals Examples: Seed dispersal by the wind or animals

12. Growth Rate The amount by which a population’s size changes in a given time. A measure of the speed of reproduction

13. Factors affecting population size The number of births. The number of deaths. Migration The movement of individuals into and out of a population Immigration Emigration

14. Types of Migration Immigration The movement of individuals into an area Emigration The movement of individuals out of an area

15. Population Dynamics Population are dynamic, meaning that they: Change in size and composition over time! Considerations: Birth rate: the number of births occurring in a given period of time Death rate or mortality rate: the number of deaths in a given period of time Life expectancy: the length of time an individual is expected to live

16. increase remain stable decrease

17. Studying Population Density Questions to be answered: Why is the birth rate unusually high (or low)? Why are more individuals dying than normal? Is there a reason for an unusually high immigration or emigration?

18. Factors affecting population Carrying Capacity (K) the maximum number of organisms a given area can support

19. Carrying Capacity The actual size of the population is usually higher or lower than the carrying capacity Below capacity Birth rate increases Above capacity Population will die or starve

20. Factors Limiting Population Limiting Factor – the resource that runs out first Helps to determine carrying capacity Examples include: Competition Predation Parasitism and disease Drought and other climate extremes Human disturbances

21. Types of Limiting Factors Density-Dependent Factors Only when the population density reaches a certain level. Density-Independent Factors Unusual weather or natural disasters Floods and fires Human activities Clear-cutting a forest or damning a river

22. What limits population growth?

23. R-Strategists Think “R” for “reproduction” Population usually NOT near carrying capacity J-curve growth (high growth rate) Exponential Growth Highly affected by abiotic factors like weather Small body size and short life span Have many offspring in a short time

24. R-strategist make lots of babies!

25. Here’s what the graph looks like!

26. K -Strategists Think “K” for “carrying capacity” Population lives near its carrying capacity S-Curve Growth Logistic Growth Highly affected by biotic factors like competition Usually large body size Have few offspring, but live a long time

27. Kangaroos are K-Strategists!

28. Here’s what the graph looks like!

29. Age-Structure Diagrams The growth of a population depends on: how many people make up the given population. The future growth of a population is predicted using: “ age-structure diagrams . ”

30. An “age-structure diagram” shows: the population of a country broken down by gender and age group. Each bar in the diagram represents individuals within a 5-year range. Males are shown to the left of the center line. Females are shown to the right of the center line.

31. Look at the age structure of population A. There are many more _________ than ______ groups. In each higher age group, there are fewer and fewer individuals. It can reasonably be predicted that population A will experience: rapid growth in the future as the large number of children reach adulthood. children older

32. Human Population Growth For most of human existence, the population grew very slowly. There were many limiting factors that kept the human population low: 1. Food was not always readily available. 2. Diseases were rampant.

33. About 500 years ago, the human population began to grow at a staggering rate. Reasons for this include: 1. The beginning of agriculture and industry made life much easier and much safer. 2. Food is available on a regular basis. 3. Goods can be shipped around the world. 4. Improved sanitation and living conditions eliminated the high levels of diseases. 5. Death rate dropped while birth rate increased.

34. As a result, the human population is experiencing ____________________. The human population ________ continue to grow in this manner. The resources on Earth are ________. exponential growth cannot limited The questions to be answered are: When will we reach the limit of these resources? How large will the population get? Will the planet be able to support this huge human population?

35. Demography is the scientific study: of human populations. Some countries today have a much higher growth rate than other countries. Birthrates, death rates, and the age structure of a population help predict why some countries have a higher growth rate than other countries.