Population Dynamics: Growth, Limits, and Interactions

1. Chapter 4 Population Ecology 4.1 Population Dynamics

2. Population Characteristics • Population Density: number of organisms per unit area • Spatial distribution: the dispersion or pattern of spacing of organisms RANDOM UNIFORM CLUMPED

3. Principles of Population Growth • Population growth rate: explains how fast a given population grows. • Population growth measured in different ways

4. Usually not linear How Fast Do Populations Grow

5. Usually slow at first Called a “J”-shaped curve Slow at first because number of reproducing organisms is small Called exponential growth: as a population gets larger it grows faster How Fast Do Populations Grow

6. Limits of the Environment • Population growth usually stops due to lack of resources • Food • Water • Shelter • Space • Population growth usually stops due to build up of waste products which poison the organisms

8. Carrying Capacity • Number of organisms of one species that an environment can support • “S”-shaped growth

9. Carrying Capacity Fluctuations above and below carrying capacity are normal

10. “J”-shaped population growth pattern • Mosquito, bacteria • Rapid Life-history pattern • Reproduce very rapidly, produce many off spring in short period of time • Environment unpredictable and change rapidly • Small body size, mature rapidly, reproduce early, short life span • Populations increase rapidly then decline

11. ”S”-shaped population growth pattern • Slow Life-history pattern • Slow rate of reproduction, produce few offspring • Elephants, bears, whales, redwood trees, cacti • Live in stable environment • Large, reproduce and mature slowly, long-lived • Maintain population size near carrying capacity

12. Environmental Limits to Population Growth • Limiting Factors: biotic or abiotic factors that regulate size of a population • Two types of limiting factors • Density dependent factors • Density independent factors

13. Density Dependent Factors • Increasing effect as population size increases • Disease • Competition • Parasites • Food • The more dense the population the faster disease can spread • Big problem in agricultural crops

14. Density Independent Factors • Affect all populations regardless of their density • Most are abiotic factors • Temperature • Floods • Storms • Drought • Habitat destruction • Pollution

15. Organisms Interactions Limit Their Population Size • Predation affects population size • Predator prey relationships often show a cycle of population increases and decreases over time

16. Predator Prey Relationships Hare Lynx

17. Predator Prey Relationships • Important for health of natural population • Usually young, old or injured are caught

18. Competition for food, water, territory are density dependent factors Only the best suited to the environment survive Effects of Competition

19. Chapter 4 Population Biology 4.2 Human Population

20. Human Population • Demography: study of human population growth characteristics: size, density, distribution, movements, birthrates, and death rates. • People live longer and they’re able to produce more children, causing the population to grow.

22. Humans can control limiting factors by: • eliminating competing organisms • increasing food production • controlling disease organisms

23. Effects of Birth and Death Rates • Birthrate : the number of live births per 1000 people in a given year. • Death rate: the number of death per 1000 people in a given year

24. How to determine the growth rate of a population? • Populationgrowth rate( PGR)= birth rate – death rate • When is PGR = 0 ? • Zero population growth exists when birthrate equals death rate.

25. Zero population growth • It means that new people are entering the population (through birth) at the same rate that people are leaving the population (through death) • The population is changing but it is stable.

26. When PGR is above zero or positive • More people are entering the population • Less people are leaving the population • Population is growing • More births than deaths in the population • When PGR is less than zero or negative • Less people are entering the population • More people are leaving the population • More deaths than births in the population

27. Doubling time: is the time needed for population to double in size • Happen with growing population ( positive PGR) • Slow growth rate means it will take longer for population to double

28. What is the age structure of a population? • Age structure: refers to the number of people at each different age level. (ex: 10- 14, 15-19) • Male or female • Is population is stable , growing , or becoming smaller?

29. Age Structure Graph: shows the age of the largest group in the population. • When a large amount of population is made up of children, then the population experiencing rapid growth. • When there are more adults than children, then the population is declining. • When the amount of population in the different age levels is about equal, then the population is stable.

30. Age Structure Graph

31. Does environment affect population growth? • Not enough food, water, or space for everyone • Population creates more waste than can be handled • Conditions of the environment cause disease to spread, or pollution affects the water

32. Homework: pages : 15-18 Due date: Monday October 10, 2016 • Test on Monday October 10, 2016 Chapters 3.1 + chapter 4 Section 3.2 Biomes will NOT be on the test • Review on Friday