1. Unit 3: Populations
Chapter 5

2. Sea otters  Sea urchins  kelp
Populations
Sea otters  Sea urchins  kelp
Long ago, hunters hunted the sea otters almost to extinction
This made the sea urchin population grow
Which in turn, made the kelp population do what? __________________

3. Populations
After sea otters were put on the endangered species list, hunters were not allowed to hunt them anymore
With hunters out of the picture, sea otter populations recovered
Which greatly decreased the sea urchins
Which greatly ___________ the kelp

4. Characteristics of Populations
Three important characteristics of population are:
Its geographic distribution
Its density
And its growth rate

5. Geographic Distribution
Geographic Distribution, or range, is a term that describes the area inhabited by a population

6. Population Density
Population Density is the number of individuals per unit area

7. Growth Rate
Growth rate is the number of births minus the number of deaths in a given area, also taking into affect immigration and emigration.

8. Factors that affect Growth Rate
Three factors can affect population size
The number of births
The number of deaths
The number of individuals that enter (immigrate into) or leave (emigrate out of) the population

9. Birthrate > Death Rate
Populations
Generally, populations grow if more individuals are born than die in any period of time
Birthrate > Death Rate

10. Populations
Birthrate > Death Rate **population growth** Birthrate = Death Rate **population remains the same** Birthrate < Death Rate **population shrinks**

11. Moving in and out
Immigration – the movement of individuals into an area
can make a population increase
Emigration – the movement of individuals out of an area
can make the population decrease

12. Exponential Growth
If a population has abundant space and food, and is protected from predators and disease, then the organisms in that population will multiply and the populating size will increase.
Exponential growth – occurs when the individuals in a population reproduce at a constant rate (i.e. bacteria, humans)

13. Exponential Growth
Under IDEAL CONDITIONS with UNLIMITED RESOURCES, a population with grow exponentially
Will show a “J-Curve” graph

15. Logistic Growth
Obviously, bacteria, elephants, and humans cannot increase in population until we cover the planet
We reach a carrying capacity, or a maximum quantity that the planet (or on smaller terms, the ecosystem) can handle

16. Logistic Growth
As resources become less available, the growth of a population slows or stops
Run out of space
Run out of food
Not enough clean water
Logistic Growth occurs when a population’s growth slows or stops following a period of exponential growth.

19. What is CARRYING CAPACITY???

20. Carrying Capacity
Carrying Capacity- The largest number of individuals of a population that a given environment can support

21. Checkpoint  What factors can change a population’s size?
What is the difference between exponential growth and logistic growth?

22. Do Fruit Flies and Rabbits Have Similar Population Growths?
Fruit Fly Population Growth
Days
Number of Fruit Flies 5 10 50 15
100 20
200 25
300 30
310 35
320 40
Graph the data provided (make 2 graphs)
QUESTIONS
What type of growth pattern is the fruit flies?
Is it the same as the rabbit’s growth pattern? Explain.
Rabbit Population
Growth
Generations
Number of Rabbits 1
100 2
105 25
1,000 37
1,600 55
2,400 72
3,350 86
8,000
13,150

23. Fruit Flies vs. Rabbits
Does either graph indicate a carrying capacity?
If so, when does the population reach this carrying capacity?
What is the maximum number of individuals that can be supported at that times?
6. Predict: Animals such as foxes and cats often prey on rabbits. Based on the growth curve of the rabbit population, what might happen if a group of predators move into the rabbits’ habitat during the tenth generation and begin eating the rabbits?

25. PDN Review
List three characteristics that are used to describe a population
What factors can change a population’s size?
What is the difference between exponential growth and logistic growth?
What is meant by population density?
Define carrying capacity.

26. Limits to Growth Back to the sea otters,
When their population declines, something has changed with their birth rates or death rates
Or between that rates of immigration and emigration
What caused the otter population to decrease to greatly??

27. Factors that impact populations
The hunters are considered a limiting factor
A Limiting Factor is a factor that causes population growth to decrease
A limiting factor that is caused by or made worse by high population (density) is known as a density-dependent factor
A limiting factor that is NOT caused by a high population is known as a density-independent factor

29. Density-Dependent Factors
A limiting factor that depends on population size is called a density-dependent limiting factor
These factors become limited only when the population density reaches a certain level
Some examples: (YOU MUST KNOW THESE!!) competition, predation, diseases, and parasitism

30. Competition
When populations become crowded, organisms compete with one another for food, water, space, sunlight, and other essentials
Competition WITHIN the population
Competition among members of the SAME species is a density-dependent limiting factor!!

31. Completion with others
Competition can also occur between members of different species
This type of competition is a major force behind evolutionary change
When two species compete for the same resources, both species are under pressure to change in ways to win and thus decrease their competition

32. Predation Populations in nature are often controlled by predation
A predator-prey relationship is one of the best mechanisms for population control
Ex: the sea otters controlled the sea urchin population… what controlled the kelp?

34. Parasitism and Disease
Parasites can also limit the growth of a population
Parasites can be microscopic bacteria to larger organisms like tapeworms and leaches
These organisms obtain nutrients from the host similar to predation, but do not kill the PREY… why not??

36. Density-Independent Factors
Density-Independent Factors affect all populations in similar ways BUT DO NOT depend on the population (meaning they will affect small groups and large)
Unusual weather, natural disasters, seasonal cycles, and certain human activities
What kind of human activities do you think??

37. Human Activities Some human activities that affect populations are:
Damming of rivers
Clear cutting forests
Local pollutions
Habitat destruction

38. Environments are always changing, and most populations can afapt to a certain amount of change
Populations often grow and shrink in response to these changes

39. Checkpoint !!
List three density-dependent factors and three density-independent factors that can limit the growth of a population
What is the relationship between competition and population size?
If an entire fox population disappears, what is likely to happen to the hare population?? How about the grass in the rabbits’ ecosystem?

40. Human Population Growth
How quickly is the world’s human population growing?
Like the populations of many other living organisms, the size of the human population tends to increase with time

41. Human Population
About 500 years ago, the human population began growing much more rapidly.
WHY???

42. A Growing Population
Agriculture and industry made life easier and safer
Food supplies became more reliable
Essential goods were able to be shipped around the globe
Improved sanitation
Improved health care

44. Demography
The scientific study of human populations is called demography
Birthrates, death rates, and the age structure of a population help predict why some countries have high growth rates while other countries grow more slowly

45. Age Structure
Population growth depends on how many people of different ages make up a given population
Demographers can predict future growth using models called age-structure diagrams

47. Age-Structure Diagrams
Equal numbers of people in each group – predicts a slow but steady growth rate in the near future
Larger number of children than adults (fat bottom) predicts a sharp population increase
Fat top, or a larger number of adults than children, predict a decrease in population

49. Future Population Growth
To predict the overal human population growth (the whole world) demographers need to consider the following:
Age structure of each country
Prevalence of life threatening diseases
AIDS, malaria, cholera

50. Human Growth Rate
It is predicted that the human growth rate will level off or even decrease by 2050
A lower growth rate means that the human population will be growing more slowly over the next 50 years
Because this growth rate is still above zero, the human population will still rise

51. Review What is the difference between immigration and emigration?
How can a predator-prey relationship serve as a population control?
Sketch the exponential growth curve of a hypothetical population
How is this different from a logistic?
How does age structure of a population affect its growth rate?