Population Dynamics

1. PopulationDynamics

2. Population Dynamics • Changes in population size and the factors that regulate populations over time.

3. Population Density • The number of individuals per unit area volume. • Example: The number of oak trees per km2 in a forest.

4. Estimation of Population Size 1. Individual counts(not always practical) 2. Transects 3. Mark-recapture method: Lincoln Index N= marked individual X total catch second time recaptured marked individuals Example: pond turtles1992: 18 1993: 34 (12) 1994: 30 (18)

5. Estimation of Population Size Example: pond turtles1992: 18 1993: 34 (12) 1994: 30 (18) 1992-93: N = 18(34) = 51 turtles 12 _________________________________________ 1993-94: N = 34(30) = 56.7 turtles 18 _________________________________________ So: 51 + 56.7 = 107.7 = 53.9 turtle estimation 2

6. Dispersion • The distribution of individuals within geographical population boundaries. • Three examples of dispersion patterns: 1. Clumped 2. Uniform 3. Random

7. Dispersion Patterns 1. Clumped a. individuals are aggregated in patches b. unequal distribution of resources in the environment. Example: trees around a lake or pond

8. Dispersion Patterns • 2. Uniform a. individuals are evenly distributed b. interactions among individuals of a population Example: creosote bushes in the desert

9. Dispersion Patterns • 3. Random a. unevenly distributed b. random dispersion is rare Example: clams in a mud flat

10. Understanding Population Growth • Exponential Growth Model Exponential growth: The rate of expansion (growth) of a population under ideal conditions.

11. Number of individuals (N) Time Exponential Growth • Example:bacteria produces a J-shaped curve

12. Understanding Population Growth 2. Logistic Growth Model logistic growth: environmental factors that restrict the growth of a population (called: population limiting factors)

13. K: Carrying Capacity • The maximum stable population size that a particular environment can support over a relatively long period of time (K).

14. Number of individuals (N) Time Logistic Growth • Example: turtles in a pond K produces a S-shaped curve

15. Draw an s-curve and draw a j-curve • Label each

16. Question • What if? • N, the number of individuals = almost 0: exponential growth • N, the number of individuals = almost K (carrying capacity): growth rate is approaching zero Zero Population Growth

17. Factors That Limit Population Growth 1. Density-Dependent Factors: a. Population-limiting factors whose effects depend on population density. b. The greater the pop, the greater the effects. Examples: 1. Limited food supply 2. Plagues 3. Predation 4. War

18. Factors That Limit Population Growth 2. Density-Independent Factors: a. Population-limiting factors (abiotic) whose occurrence is not affected by pop density. b. the greater the pop, the greater the effects Examples: 1. Earthquakes 2. Fires 3. Hurricanes 4. Freeze in the fall

19. number of individuals in pop. Time Boom and Bust Species • A rapid increase (boom) in a population followed by a sharp decline (bust). • Examples: a. Daphnia in a pond boom bust

20. number of individuals in pop. Years Boom and Bust Species • Sometimes species(carnivore) depend on other species (prey) for food. • Example: Snowshoehare and lynx

21. Evolution Shapes Life Histories • Life History: Series of events from birth through reproduction to death. • Two basic types of life history strategies: 1. Opportunistic life history (r-selected species) 2. Equilibrial life history (K-selected species)

22. 1. Opportunistic life history(r-selected species) Characteristics: 1. maturing time: short 2. life span: short 3. mortality rate: often high 4. times female is reproductive: usually once 5. age at first reproduction: early 6. size of offspring: small 7. parental care: none 8. Size of organism: small

23. 2. Equilibrial life history(K-selected species) Characteristics: 1. maturing time: long 2. life span: long 3. mortality rate: often low 4. times female is reproductive: often many 5. age at first reproduction: late 6. size of offspring: large 7. parental care: often extensive 8. Size of organism: tend to be large

24. Life History Examples r-selected species: 1. Garden weeds 2. Insects 3. Desert flowers K-selected species: 1. Humans 2. Apes 3. Elephants

25. % of survivors % of maximum life span Survivorship Curves • Type 1 survivorship curve: High survival rates until old age. Example: humans

26. % of survivors % of maximum life span Survivorship Curves • Type 2 survivorship curve: Intermediate between the extremes. Example: squirrel

27. % of survivors % of maximum life span Survivorship Curves • Type 3 survivorship curve: High mortality rates as larvae but decreased mortality at later ages. Example: oysters frogs insects

28. Human Population Growth • Age structure Proportions of individuals of a population in different age groups. A typical population has three main age groups (age structure). 1. Pre-reproductive 2. Reproductive 3. Post-reproductive

29. Post-reproductive Reproductive Pre-reproductive Age Structure

30. Human Population Growth Today • Human population as a whole is growing exponentially. • Has doubled (doubling-time) three times in the last three centuries (doubled the carrying capacity several times). • Is now 6.5 billion, might reach ~8 billion by 2020.

31. Question: • What are the reasons for the increase in human population? • Answer: 1. Improved health 2. Technology 3. Decreased death rates

32. Question: • What is Zero Population Growth (ZPG)? • Answer: a. birth rate equals death rate. b. intrinsic growth (r) = 0

33. Question: • What are two ways the human population can reach Zero Population Growth? 1. Limit the # of offspring per couple a. Reduces family size b. Voluntary contraception c. Family planning 2. Delay reproduction (late 20’s instead of early 20’s)