Population Principles

1. Population Principles Chapter 3

2. Population Characteristics • Population - Group of individuals of the same species inhabiting the same area simultaneously. (6.4 Billion – 2004) • Natality and Mortality • Natality - Number of individuals added through reproduction. • Birth Rate (Humans Born / 1,000) • Mortality - Number of individuals removed via death. • Death Rate (Humans Died / 1,000)

3. Figure 7.1

4. Population Characteristics • Population Growth Rate - Birthrate minus the death rate. Often expressed as a percentage of the total population. (Geometrically – Population)(Arithmetically – Food Supply) • Survivorship Curve - Shows proportion of individuals likely to survive to each age. • High mortality in young. • Mortality equitable among age classes. • Mortality high only in old age.

5. Survivorship Curve (Fig.7.2)

6. Sex Ratio and Age Distribution • Sex Ratio - Age Distribution • Sex Ratio - Relative number of males and females in a population. • Females determine the number of offspring produced in sexually reproducing populations. • Age Distribution - Number of individuals of each age in the population. • Greatly influences population growth rate.

7. Age Distribution in Human Populations (Fig.7.3)

8. Population Density and Spatial Distribution • Population Density - Number of individuals per unit area. • High population may lead to increased competition for resources. • Dispersal - Movement of individuals from densely populated locations to new areas. • Emigration - Movement from an area. • Immigration - Movement into an area.

9. Population Growth Curve • Biotic Potential - Inherent reproductive capacity. (Biological ability to produce offspring) • Generally, biotic potential is much above replacement level. • Natural tendency for increase. • All living populations follow an exponential growth curve.

10. Exponential Growth Curve • Lag Phase - First portion of the curve; slow population growth. • Exponential Growth Phase (Log Phase)- More organisms reproducing causing accelerated growth; continues as long as birth rate exceeds death rate. *Currently* • Stable Equilibrium Phase - Death rate and birth rate equilibrate; population stops growing.

11. Biotic Potential (Fig.7.4)

12. Typical Population Growth Curve (Fig.7.5)

13. Carrying Capacity • Carrying Capacity - Number of individuals of a species that can be indefinitely sustained in a given area without harming the habitat.

14. Environmental Resistance • Environmental Resistance - Any factor (limiting factor) in the environment limiting carrying capacity. • Four main factors: • Raw Material Availability • Energy Availability • Waste Accumulation and Disposal • Organism Interactions • Disease, Predation, and Space

15. Carrying Capacity (Fig.7.6)

16. Bacterial Growth Curve (Fig.7.7)

17. Fig. p.138

18. Reproductive Strategies and Population Fluctuations • Not all species reach a stable carrying capacity. • Species can be broadly lumped into two categories: • K-strategists • r-strategists

19. K - Strategists • Large organisms • Long-lived • Produce few offspring • Provide substantial parental care • Populations typically stabilize at a carrying capacity. • Usually occupy relatively stable environments. • Reproductive strategy is to invest in a few, quality offspring.

20. K - Strategists • Controlled by density-dependent limiting factors. • Factors that become more severe as the size of the population increases. • Diseases • Deer - Lions - Swans

21. r - Strategists • Small organisms • Short-lived • Produce many offspring • Little if any parental care • Usually do not reach carrying capacity (boom-bust cycles). • Exploit unstable environments. • Reproductive strategy is to produce large numbers of offspring to overcome high mortality.

22. r - Strategists • Controlled by density-independent limiting factors. • Population size is irrelevant to the limiting factor. • Weather Conditions • Grasshoppers - Gypsy Moths - Mice

23. Population Cycles (Fig.7.8)

24. Human Population Growth • Major reason for increasing human population growth rate is an increase in medical care, and a consequential decrease in death rates.

25. Historical Human Population Growth (Fig.7.9)

26. Doubling Time • Doubling Time of a Population (years) : • 70 / Population Growth Rate (%) ( 70 / 2.0% = 35 years )

27. Doubling Time for the Human Population (Fig.7.10)

28. Human Population Growth • Interactions Affecting Carrying Capacity • Available Raw Materials • Available Energy • Waste Disposal • Interaction With Other Organisms

29. Social Factors Influence Human Population • Humans are social animals who have freedom of choice. • People make decisions based on history, social situations, ethical and religious beliefs, and personal desires. • Biggest obstacles to controlling human population are not biological, but are the province of philosophers, theologians, politicians, and sociologists.

30. Ultimate Size Limitation • If the world continues to grow at current rate, population will surpass 12 billion by 2060. • Human population subject to same biological constraints as other species. • Human population will ultimately reach a carrying capacity and stabilize. • Disagreement about exact size and primary limiting factors.

31. Elephant Trade

32. Snow Goose (Pg.145)