Biology 120                      Handout: Population Growth                                     R. Irwin

Environmental Concerns:

Some areas of concern:

Some human activities that lead to environmental problems:

Ecology: scientific study of organisms in their environments

Growth of the Global Human Population:

Models of population growth:

Aspects of populations:

Exponential growth:  model that assumes r constant:

Logistic growth:  model that assumes r decreases as population size increases, because of intraspecific competition for resources.

J-shaped curve:

Application of population models to humans:


Initially, the human population grew exponentially worldwide.

 

Recent changes in developed versus developing countries:

Developed Countries

Impact on population growth

Developing Countries

Impact on population growth

Improved medicine, vaccines, better sanitation

 

 

Improved medicine, vaccines, better sanitation

 

 

Decrease in per capita birthrate (b)

 

 

 

No change in per capita birthrate (b) so it is higher than developed countries.

 

 

Practice Questions:
1. All individuals of the same species within an area make up a(n) ____________________
2. All species occurring together in an area make up a(n) __________________________
3. All species occurring in an area plus all non-living aspects of the environment with which they interact make up a(n) ____________________
4. All factors required for a population of a species to exist in an area are referred to collectively as the ______________________ of that species
5. The scientific study of organisms in their envrionment is called ___________________________.
6. The model of population growth in which birthrates and deathrates are constant is called __________________.  Suppose a population is growing according to this model.  It takes 4 years for the population to go from having 30 individuals to having 60 individuals.  How long will it take from the time there are 60 individuals to the time there are 120 individuals?
7.  A population is growing according to exponential growth.  You find that in five years, the population size changes from 70 to 140.  How large will the population be five years after that?  Draw a graph that shows population growth for this population.  Be sure to label your axes.
8. According to to the exponential growth model, the rate of population growth (G)
     a. decreases as the population grows larger
     b. stays the same as the population grows larger
     c. increases as the population grows larger
     d. first increases, then decreases, as the population grows larger
9.  According to the logistic growth model, the rate of population growth (G)
     a. decreases as the population grows larger
     b. stays the same as the population grows larger
     c. increases as the population grows larger
     d. first increases, then decreases, as the population grows larger
10.  Define carrying capacity (K).
11.  Draw a graph of logistic growth if the carrying capacity is 60 individuals.  Be sure to label your axes.
12.  A population is at carrying capacity. What is the value of the population growth rate?
13.  Distinguish between the population growth rate (G) and the per capita growth rate (r)
14. When a population grows according to logistic growth, the per capita growth rate decreases as the population grows; this kind of growth is called ____________________.  This kind of change would occur because birthrates ________________ (increase or decrease) or because deathrates ________________ (increase or decrease).  What is happening in the environment to cause these changes in birthrate and/or deathrate?
15. Which part of the equation for logistic growth causes the per capita growth rate to be density dependent?  Show why, mathematically, by showing how the value of this part of the equation differs between large and small populations and how this affects growthrate.
16.  When a population growing logistically is very small, its growth rate is:
     a. about the same as a population growing exponentially
     b. much higher than a population growing exponentially
     c. much lower than a population growing exponentially
     d. zero
17.  A population is growing according to a J-shaped curve.  It will:
     a. grow up to the carrying capacity, then decline to zero
     b. continue growing faster and faster indefinitely
     c. grow to a population size that is above the carrying capacity, then decline to zero
     d. grow to the carrying capacity, at which point the population growth rate will become zero
18. Why can a population not keep growing exponentially forever?  What does this indicate about the human population?
19.   What is meant by intraspecific competition for resources?  What is the effect of intraspecific competition for resources expected to be on birthrate?  on deathrate? on population growth rate?
20.  A population is growing logistically.  At what population sizes will the growth rate be increasing?  At what population sizes will the growth rate be positive, but decreasing?  At what population size will the growth rate be zero?  At what population sizes will the growth rate be negative?
21.  Describe how birthrates and deathrates in developed countries have changed since industry/modern medicine developed.  How has growth rate changed as a result?
22.  Describe how birthrates and deathrates in developing countries have changed since industry/modern medicine developed.  How has growth rate changed as a result?
23.  Population growth rate is currently:
     a. higher in developed than developing countries, because modern medicine has allowed increased survival resulting in a decreased deathrate
     b. higher in developed than developing countries, because modern medicine allows us to have larger families of surviving offspring
     c. higher in developing than developed countries, because of the lower deathrate in developing countries
     d. higher in developing than developed countries, because of the higher birthrate in developing countries
24. What social or economic factors have been proposed as likely to explain the fact that the birthrate of developed countries has decreased but the birthrate of developing countries typically has not?
25.  Evaluate each of the following as a factor that could explain the difference in birthrate between developed and developing countries by explaining why it could explain the difference.  If we've discussed it, also discuss the evidence that this factor is or is not important (is it strongly associated with birthrate differences?  Are there exceptions that suggest that it does not always explain the difference?) (i) cultural/religious beliefs (ii) availability of birth control  (iii) infant mortality level (iv) education level of women (v) farming vs. non-farming as main source of income and food
 

HOMEWORK #1 over Raloff, J. (1996) "The Human Numbers Crunch":

1. Explain (from lecture) what is meant by the carrying capacity of a species in an environment. Give two reasons why, according to Raloff, this concept can not be applied well to human populations even though it applies to other animals.

2.  The number of humans in the world affects CO2 emission levels, which are thought to be contributing to global climate change.  According to Lutz (as discussed by Raloff), what must be measured in addition to the number of humans born in a society with particular level of wealth and technology in order to accurately measure the impact of human populations on increasing CO2 emissions?  Why does this factor also affect CO2 emissions?  Give two ways in which human society has been changing that lead to an increase in this factor, and, as a result, to an increase in CO2 emissions.