1. Populations Chapter 19

2. Understanding Populations Section 19.1

3. Definition:   A group of organisms of the same species living in the same place at one time

4. Thomas Malthus (1766-1834)  Essay on the Principal of Population  In nature, plants and animals produce far more offspring than can survive  Man, too, is capable of overproducing if left unchecked  Famine and poverty are natural outcomes of overpopulation

5. 3 Characteristics: 1. Size 2. Density 3. Dispersion

6. Population Size  # of individuals in a given area  Difficult to measure  Estimates often taken

7. Population Density  How crowded a population is  # of individuals per unit area  Ex) 30 people/classroom

8. Population Dispersion  Spatial distribution of individuals 1. Clumped - social flocks or herds - clump around resources - most common 2. Even - due to competition among individuals to maximize distance 3. Random - pattern-less - rare in nature - ex) snakes, clams, dandelion

9. Population Dynamics  Populations change over time due to:  Birth rates  Death (Mortality) rates  Life expectancy rates  Age Structure  Patterns of Mortality

10. Age Structure  Distribution of individuals among different ages in a population

11. Survivorship Curve

12. Survivorship Curves  Type I – death at old age –humans  Type II – death at any age –Birds, many reptiles  Type III – death at young age –Plants, many insects

14. Measuring Populations Section 19.2

15. Population Growth Rate  # by which a population’s size changes over time  Population changes by:   1. birth rate   2. death rate   3. emigration   4. immigration

16. Calculations  ADDS to population = birth & immigration  SUBTRACTS from population = death & emigration  ASSUME immigration = emigration  THEREFORE: birth rate – death rate = growth rate

17. 2 Models of Growth 1. Exponential Model J-shaped curve 2. Logistic Model S-shaped curve

18. Exponential Model   At a steady, positive growth rate, the population will add a larger # of individuals with each generation   The larger the population gets, the faster it grows!   Limitation: only exists under rare conditions

19. Logistic Model   The exponential model accounting for the influence of limiting factors   Carrying capacity (K): # of individuals the environment can support of a long period of time – –Fluctuates slightly

20. Limiting Factors   condition that restricts growth of a population ex) space, food, accumulation of waste

21. Carrying Capacity

23. Population Regulation  2 types of limiting factors  1. Density-independent factors –Abiotic factors –Reduction of population by same proportion no matter what size it is –Ex) floods or extreme temp. extreme temp.

24.  2. Density-dependent factors –Biotic factors –The larger the population, the larger the proportion of reduction. –Ex) disease or starvation

25. Human Population Growth, 19.3 video

26. History Lesson  Hunter-gatherer lifestyle: slow human growth because of high mortality rate  Agricultural revolution: human population growth because of an increase in the food supply  Industrial revolution: rapid human population growth because of decline in death rates  video video

27. Today’s Growth  Developed Countries: 20% of world’s population, low growth rates –Ex) USA, Japan, Germany, France, etc.  Developing Countries: 80% of world’s population, high growth rate –Ex) Central America, South America, Asia, Africa