2. Understanding Populations

3. The Human Population From 1900 to 2003, the population tripled in size to reach 6.3 billion people Today, the human population count is over 7 billion and we are projected to reach 9 billion within the next 50 years While our population has increased, others have dramatically decreased

4. Human population growth What factors have contributed to this exponential growth pattern? 1650  500 million 2013  7 billion Industrial Revolution Significant advances in medicine through science and technology Bubonic plague "Black Death" Population of… China: 1.3 billion India: 1.2 billion adding 75 million/year

5. Properties of Populations For example, all of the bass in a pond are considered a population, because they are isolated in the pond and don’t interact with bass living in other ponds Populations are a group of organisms that belong to the same species and live in a particular place at the same time They can be widely distributed, or confined to a small area

6. Properties of Populations Boundaries can be imposed by environmental features, or they can be arbitrarily chosen to simplify a study of the population Population studies focus on a population as a whole – how many individuals are born, how many die, and so on

7. Properties of Populations Three main characteristics of populations: 1) Population Size 2) Population Density 3) Dispersion

8. Population Size How many blades of grass are in this football field? The number of individuals that the population contains Size is a fundamental population property and can be difficult to measure directly, so sometimes we must estimate

9. Population Size How many oak trees are in this forest that is 10 km 2 ? Extrapolate Count how many are in 1 km 2 and multiply by 10.

10. AP Biology Difficult to count a moving target Measuring population size  How do we measure how many individuals in a population?  number of individuals in an area  mark & recapture methods sampling populations

11. Population Density A measure of how crowded a population is Expressed as the number of individuals per unit of area or volume

12. Dispersion From Latin dis- meaning out and spargere- meaning to scatter The spatial distribution of individuals within the population

13. Types of Dispersion Clumped – individuals clustered together Uniform – separated by a fairly consistent distance Random – each individual’s location is independent of the locations of other’s

14. Clumped Distributions Occur when resources such as food or living space are limited Occur because of species social behavior (flocks)

15. Uniform Distributions Result when individuals within the same habitat stay as far away from each other as possible When a bird locates its nest so it’s not close to other birds nests.

16. Random Dispersion Few populations are truly randomly dispersed Usually they show degrees of clumping or uniformity Also depends on the scale at which the population is being observed

17. Population Dynamics All populations are dynamic – they change over time Look at birth rate, death rate, and life expectancy

18. Population Dynamics Birth Rate: the number of births occurring in a period of time Death/Mortality Rate: the number of deaths in a period of time Life Expectancy: How long an individual is expected to live US Population Dynamics Birth Rate/yr4 million Death Rate/yr2.6 million Life ExpectancyM = 74 yrs F = 80 yrs

19. Comparing Population Properties and Population Dynamics

21. Age Structure The distribution of individuals among different ages in a population Often presented as graphs Many important population processes vary with age

22. AP Biology Age structure  Relative number of individuals of each age What do the data imply about population growth in these countries? A C B

23. Patterns of Mortality Mortality data tends to match one of three curves on a graph Known as survivorship curves These show the probability that members of a population will survive to a certain age

24. Patterns of Mortality Type I – Death late in life (humans) Type II – Probability of dying doesn’t change (birds) Type III – More likely to die young (salmon)

25. TRUE TRUE OR FALSE: A population consists of individuals of the same species living together in one place at the same time.

26. FALSE – IT REFERS TO THE DISTRIBUTION OF THE INDIVIDUALS OF A PARTICULAR POPULATION WITHIN A PARTICULAR AREA TRUE OR FALSE: Dispersion is the term for how populations are distributed within a ecosystem.

27. FALSE – BOTH CAN FLUCTUATE TRUE OR FALSE: The birth rate in a population equals the death rate.

28. Measuring Populations A single pair of elephants can increase to a population of 19 million individuals within 750 years! Why haven’t they increased their numbers?

29. Population Growth Rate The amount by which a population’s size changes in a given time Whether a population grows, shrinks, or remains the same size depends on: Birth Death Immigration Emigration

30. Population Growth Rate Immigration – movement of individuals into a population Emigration – movement of individuals out of the population Immigration & birth add to a population Emigration & death subtract from a population Assume immigration = emigration

31. Population Size Demographers divide large populations into groups of 1,000 and to present data per capita, meaning per individual Birth rates, death rates, and growth rates for large populations are usually expressed per capita

32. Population Size Example: If there are 52 births and 14 deaths per 1000 individuals per year: Birth Rate = 52/1000 = 0.052 births per capita per yr Death Rate = 14/1000 = 0.014 deaths per capita per yr Growth rate can be calculated by: Birth rate – Death Rate = Growth Rate

33. Population Size Calculating per capita growth: 0.052 births per capita – 0.014 deaths per capita = 0.038 growth per capita A positive growth rate means population is growing; negative means it’s shrinking

34. Population Size To find the number of new individuals that will be added to the population in a year, just multiply the per capita growth rate by the number of individuals in the population Ex] Population = 50,000 Growth = 0.038 per capita 0.038 x 50,000 = 1900

35. The Exponential Model At a steady positive growth rate, the population will add a larger number of individuals with each generation A pattern of increase in number due to a steady growth rate is exponential growth

36. The Exponential Model A graph of the population size over time for exponential growth makes a J- shaped curve Population size grows slow when small, but increases as individuals join the population

37. The Exponential Model Leads us to predict that population size will increase indefinitely and by a greater number with each time period Do you think this trend will continue? What will the graph look like in the future?

38. Applying the Exponential Model This model matches observed patterns of growth of real populations, but only under a certain number of conditions and for a limited period of time Example] Bacteria can grow exponentially if provided with an abundance of food and space and if waste is removed

39. Applying the Exponential Model This doesn’t apply to most populations because resources aren’t unlimited and harmful waste accumulates Any factor, such as space, that restrains the growth of a population is called a limiting factor All populations are limited by their environment

40. Applying the Exponential Model As a population grows, competition intensifies for resources Thus, each individual’s ability to fight off disease, grow, and reproduce decreases This results in a decreasing birth rate and increasing death rate

41. The Logistic Model Builds on the exponential model but accounts for the influence of limiting factors Carrying capacity (K) is the number of individuals the environment can support over a long period of time

42. The Logistic Model The graph of this model looks like a stretched-out letter S When population is small, birth rates are high and death rates are low, so looks like exponential growth As size approaches K, the growth rate slows At K, the birth rate = death rate and growth stops

43. Contains some assumptions K is constant and doesn’t fluctuate with environmental changes Reality is, it does. Ex] It is greater when prey is abundant and lower when it is scarce.

44. The logistic and exponential models are not universal representations of real populations – but – they are an important tool that scientists use to explain population growth and regulation.

45. True or False: Carrying capacity is the number of individuals the environment can support for an extended period of time. True!!!

46. True or False: Population growth can be predicted using only birth- and death-rate statistics. False – Immigration and emigration rates are important factors to consider!!!

47. How many new individuals will there be next year in a population of 85,000 people if there are 98 births and 75 deaths per thousand people? 0.098 births per capita – 0.075 deaths per capita = 0.023 growth per capita 0.023 x 85,000 = 1955 new individuals