1. Chapter 5
Populations

2. How are these terms related?
species
population
community
What they have in common:
What makes them unique
How will you remember?

3. 5-1 How Populations Grow Objectives:
List the characteristics used to describe a population
Identify factors that affect population size
Differentiate between exponential and logistic growth

4. Characteristics of Populations
Four Characteristics:
Geographic range
Density and distribution
Growth rate
Age structure

5. Geographic Range Area covered by a population
Size depends on organism and other limiting factors
Distribution of long-tailed salamanders Eurycea longicauda

6. Population Density Refers to the number of individuals per unit area
A B
Can vary greatly among species in the same ecosystem

7. What is the population density?
1 m
5 m
10 butterflies/5 m2
= 2/m 2

8. Distribution
Distribution refers to how members of a populations are spaced out across the range of that population
Can be described in one of 3 ways:
Random
Uniform
Clumped

9. Ways to Determine Population Size
1. Direct Observation- counting one by one
2. Indirect Observation- relies on signs like tracks, empty nests
Useful when organisms are difficult to observe
3. Sampling- uses an estimate (an approximation of a number based on reasonable assumptions)
4) Mark and Recapture- another way of estimating the population

10. Mark and Recapture
Scientists capture and mark members of a species and then release them
Later the species is captured again and the marked members are counted to estimate the population
Total population = number marked x number captured = 5 x 4 = 20
number captured with marks
Captured Species =4
Number with marks = 1
Marked Species = 5

11. Population Growth Population size is affected by: 1. Births and deaths
Births>Deaths= population grows
2. Immigration and emigration
Organisms immigrate into and emigrate out of populations to find mates, food, establish new territories, etc.
Immigration>emigration=population grows
3. Limiting Factors
- Space, food, predators, disease, etc.

12. Patterns of Population Growth
Exponential growth- occurs when the number of organisms rises at an ever-increasing rate
Occurs when conditions are ideal
no limiting factors affecting population
Population reproduces at a constant rate
i.e. binary fission (reproduction) in bacteria occurs every 20 minutes
Can result in a population explosion

13. J-shaped Curve Shows exponential growth (unchecked growth)
Initial increase in number of organisms is slow because the number of reproducing organisms is small
Rate increases rapidly because the total number of potential reproducers increases

14. Patterns of Population Growth
Logistic growth- occurs when a population’s growth slows or stops following a period of exponential growth
Growth pattern of natural populations
Due to limited availability of resources when populations increase in size

15. S-shaped Curve Shows logistic growth
A= lag phase-small # of reproducing individuals
B= exponential growth
C= population growth levels off
carrying capacity (K)- number of organisms of a population that a particular environment can support over an indefinite period of time
Determined by limiting factors C B A

16. Logistic Growth

17. 5-2 Limits to Population Growth
Limiting factors- factors that controls the growth of a population
Determine the carrying capacity of an environment
Two types:
Density dependent- affect increases as population density increases
Density independent- affect is the same regardless of population size

18. Types of Limiting Factors
Density-dependent
competition
predation
herbivory
parasitism
disease
Density-independent
temperature
floods
drought
habitat disruption

19. Competition
Constant competition for resources within the same population (intraspecific) or between populations (interspecific)
Can lead to evolution (speciation)

20. Predation Cyclical in nature which increases and decreases over time
Important for the health of natural population

21. Parasitism and Disease
Also limit population growth

22. 5-3 Human Population Growth
Objectives:
Discuss the trend of human population growth
Explain why population growth rates differ from country to country

23. History of Human Population Growth

24. Industrial Revolution and Human Population
Living conditions improved and more reached reproductive age
Food supplies became more reliable
Improved nutrition
Sanitation
Medicine
Healthcare
Led to exponential growth of population

25. Thomas Malthus
Suggested that populations would be regulated by war, famine, an disease
Limiting factors:
Competition (war)
Limited resources (famine)
Parasitism (disease)
Malthus’ ideas influenced Charles Darwin

26. Patterns of Population Growth
Demography- scientific study of human population
examines characteristics of human populations and attempts to explain how those populations will change over time
Characteristics examined:
Birth rates
Death rates
Age structure

27. Demographic Transition
Population growth in developed countries like US, Europe, and Japan has slowed dramatically
these countries have completed the demographic transition, a dramatic change in birth and death rates
Birth rate falls to meet the death rate and population stops growing

28. Demographic Transition
STAGE I
Reproduction and death rates are high throughout most of history
STAGE II
Death rates fall, but birth rates remain high for some time; births exceed deaths and population grows exponentially
STAGE III
Standard of living and education level rises and birthrate falls causing population to level off

29. World Population Growth

30. Age Structure
Population growth depends, in part, on how many people of different ages make up a given population.
Demographers can predict future growth using models called age-structure diagrams
Age-structure diagrams show the population of a country broken down by gender and age group.

31. Age Structure Diagrams

32. Future Population Growth
Considerations for predicting world population growth:
Age structure of each country
Prevalence of life-threatening disease
Prediction for 2050 is slowing growth, but still 9 billion
Increasing population, regardless of rate, could have negative impact on environment and global economy
Or, will be offset by science, technology and changes in society