Chapter 17 Lecture Outline See PowerPoint Image Slides

1. Chapter 17 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.

2. Population Characteristics • A population is a group of organisms of the same species located in the same place at the same time. • A species is the largest possible population. • Usually the term population is used to describe portions of a species.

3. Gene Frequency • A measure of how often a specific gene shows up in the gametes of a population • Two populations of the same species can have very different gene frequencies.

4. Gene Flow • The movement of a gene • From one generation to another • From one population to another when animals migrate • Both types of gene flow usually occur together.

5. Age Distribution • The number of organisms in each age in the population • Organisms are grouped by their reproductive status. • Prereproductive juveniles • Reproductive adults • Postreproductive adults

6. Age Distribution • The age categories of a population may not contain the same number of individuals. • The age structure of some species will change dramatically over the course of a season. • Birds, flowering plants • Age structure impacts how fast the population will grow.

7. Age Distribution in the Human Population

8. Sex Ratio • The number of males compared to the number of females • Birds and mammals • Those that have mate-bonding frequently have a 1:1 ratio of males to females. • Those without mate-bonding usually have more females than males. • Harems • Insects usually have far more females than males. • Sex ratios do not apply to hermaphroditic species.

9. Population Distribution • Describes the way individuals within a population are arranged with respect to one another • Three basic arrangements • Even, random, clumped

10. Population Density • The number of organisms of a species per unit area • Population density varies with • Success of the individuals • Resources available • Populations that are highly concentrated will begin to experience competition. • Population pressure describes how the intensity of competition causes dispersal. • Dispersal relieves the pressure and can lead to new populations. • If dispersal doesn’t happen, then individuals will begin to die.

11. Reproductive Capacity • The theoretical number of offspring that could be produced by a population • Also called biotic potential • Usually larger than the number of offspring needed to maintain the population

12. Reproductive Capacity • Two strategies for maintaining the species • Have a lot of offspring, but not invest a lot of energy in them after birth • The probability of survival to reproductive age is slim. • Have fewer offspring, but invest a lot of energy in them after birth • The probability of survival to reproductive age is quite good.

13. The Population Growth Curve • The growth of a population is dependent on • The rate at which organisms enter the population • Immigration and birth • Natality = the # of new individuals added by birth/1000 individuals • The rate at which organisms leave the population • Emigration and death • Mortality = the # of individuals leaving by death/1000 individuals

14. The Population Growth Curve • Population growth curves graph the change in population size over time. • Four phases can be seen in the curve. • Lag phase • Exponential growth phase • Deceleration phase • Stable equilibrium phase

15. A Typical Population Growth Curve

16. Lag Phase • A period of time immediately following the establishment of the population • Population is small • Growth is happening slowly • Both natality and mortality are low • Occurs slowly because reproduction takes time

17. Exponential Growth Phase • The period of time when the population is growing rapidly. • As the number of individuals increases, then there are more individuals available to reproduce. • During this phase, populations increase by the same percent each year. • Natality is greater than mortality. • Mice population • Two mice mate and have 4 • Those four mate and have 8 • Those eight mate and produce 16

18. Deceleration Phase • Occurs when population growth rate begins to slow • Population continues to grow until birthrate and deathrate become equal

19. Stable Equilibrium Phase • The period of time when the population stops growing • Maintains a stable size • Exponential growth cannot continue indefinitely. • The availability of resources will limit population growth. • When a population becomes large enough, resources will be in short supply. • Mortality will increase to the point where it equals natality. • Large organisms that live a long time tend to reach stable equilibrium.

20. Alternate Population Growth Strategies • K-strategists are large organisms that a live long time and reach a population size that can be sustained (as just described). • r-strategists are small organisms with short lifespans and tend to have fluctuating population that do not reach a stable equilibrium phase • Characterized by a “crash” after rapid exponential growth

21. Population Growth Curve for Short-lived Organisms

22. Limits to Population Size • Factors that determine the size at which a population will reach stable equilibrium • Called limiting factors • Collectively known as environmental resistance

23. Extrinsic and Intrinsic Limiting Factors • Extrinsic factors come from outside the population and limit population growth. • Predators, availability of nutrients, natural disasters • Intrinsic factors come from within the population and limit population growth. • Crowded conditions leading to • Decreased reproduction • Decreased # of offspring produced per reproductive event • Decrease in maternal care • Increase in death rates

24. Density Dependent Limiting Factors • These factors become more effective at limiting population size as the population gets bigger. • Predators are more likely to capture individuals in a large population. • Disease epidemics are more common in large populations. • Competition for resources increases as population size increases. • Intrinsic factors such as decreased reproductive rates occur as population size increases. • Populations of large, long-lived organisms are usually controlled by these factors.

25. Density Independent Limiting Factors • These factors control population growth no matter how large the population is. • Usually accidental extrinsic factors • Weather patterns • Natural disasters • Drought/excessive rainfall • Populations of small, short-lived organisms are often controlled by these factors.

26. Categories of Limiting Factors • Factors that limit population growth can be categorized as • Availability of raw materials • For plants • Nitrogen, water, magnesium • For animals • Water, minerals, materials/sites for housing/nesting, food (as a source of carbon and nitrogen) • Availability of energy • Availability of light to plants • Availability of food to animals

27. Categories of Limiting Factors • Production and disposal of waste products • Usually not relevant for plant species • Animal species generate more waste. • Waste can be toxic. • As waste builds up, reproduction slows, death rates increase. • Accounts for the death phase in bacteria • Follows stable equilibrium phase

28. Bacterial Population Growth Curve

29. Categories of Limiting Factors • Interactions with other organisms • Predation, parasitism and competition limit population growth. • These interactions usually • Involve more than one population • Limit the size of both populations involved • Generate population cycles • Lemming example • Mutualistic interactions allow populations to grow at a faster rate than they would have alone.

30. Population Cycles

31. Carrying Capacity • Populations at stable equilibrium phase have reached their maximum size for that environment. • This maximum, sustainable population size is called carrying capacity. • Determined by a set of limiting factors • Environmental changes, succession, disease, and natural disasters can change carrying capacity for a given population. • The size of the organism and the size of its habitat can determine carrying capacity.

32. Carrying Capacity

33. The Effect of Biomass on Carrying Capacity

34. Limiting Factors to Human Population Growth • Human populations follow the same pattern of growth. • They are limited by the same kinds of factors. • The human population growth curve • Shows the lag and exponential phases • Although the human population has approached carrying capacity for some time, • Technology continues to increase carrying capacity. • Nevertheless, limiting factors will cause human population growth to level off.

35. Human Population Growth Curve

36. Available Raw Materials • Include • Drinking water • Irrigation water • Iron ore • Silicon • Food • Many portions of the global human population do not have enough food. • However, the world can produce enough food to feed everyone. • Political and economic barriers prevent equal distribution of food.

37. Availability of Energy • Ultimately, humans depend on sunlight for energy. • Solar energy can be stored in fossil fuels. • However, limited reserves of petroleum, natural gas and coal exist. • It is hard to predict how long these will last. • Rate of use of the reserves increases as population size increases. • It took millions of years to build up these reserves, but we are using them at a rate that will deplete them in a matter of hundreds of years.

38. Production of Wastes • Human biological wastes can be decomposed by detrivores. • Technological wastes cannot be decomposed by organisms. • Excess technological wastes cause pollution. • Most of this waste is toxic and is damaging the environment.

39. Interactions with Other Organisms • Humans interact with other species in many ways. • We are hosts for a variety of parasites. • Bacteria and viruses • We are predators of a number of species. • We have mutualistic relationships with • Domesticated and wild animals • A number of plant species • A variety of bacterial species

40. Interactions with Other Organisms • We compete with other species for resources. • Because we win, we frequently displace other species. • This has caused a number of extinctions. • We compete with one another for resources. • Evident in an increase in infant mortality

41. Control of Human Population is a Social Problem • Humans are able to predict the outcome of a specific course of action. • We have the information to control the human population and improve health and quality of life. • However, we do not always make the best unbiased decisions. • We tend not to consider what is best for the population. • We tend to consider what is best for us, individually.

42. Control of Human Population is a Social Problem • Continued population growth will present more social, political and economic problems than biological problems. • Will likely result in increased famine and starvation • One major factor seems to be the educational status of women. • Women with higher levels of education have fewer children. • Improving the education of women may be one social strategy for limiting population growth.