Lecture:
Linear vs. Exponential growth – imagine a salmon farm pen population… linear (add net pop interval each
year) exponential (allow multiplication by a constant factor (not necessarily 2))
Pop growth is a function of fertility, mortality, migration
Population density vs carrying capacity
Human and Marine Ecology Lab
Name:
Objectives:
1) Understand the exponential nature of human population growth.
2) Study examples of organisms representing typical marine trophic levels.
3) Become familiar with humanity’s impact on the oceans and marine life.
Go to the Earth Systems Laboratory and open a browser to the web address for this exercise:
http://geosci.sfsu.edu/courses/g103/labs/new/ecology
PART I: Assessing human population growth
1. Graph the human population estimates and projections provided on the web page for this exercise. Plot
the population every 100 years, from 1000 to 2050. Be sure to label your axes and connect each successive
data point with a straight line.
Is the global human population still growing? Is the growth linear or exponential?
2. Based on your graph, how many years did it take for the human population to double before and after
1700? Given the equation (doubling time in years)=70/(percent annual growth rate), determine whether the
percent annual growth rate of the human population has decreased, remained constant, or increased over
time? Show your work.
3. When do you think the human population explosion occurred? Give two reasons why it might have
occurred during that period of human history.
PART II: Humans and the marine food chain
As the human population grows the demand for food from the sea increases. In response, technological
innovations that make fishing more efficient are valued at the market. Past and present experience reveals
that such economic demand can drive ocean species to extinction. Search the web and the recommended
links to learn how humans have influenced the populations of some (edible) marine animals and answer the
following questions.
4. For each of the trophic (or food chain) levels below, list (at least one) marine and land organism/s that
humans eat. Search the web if you cannot think of an example.
Marine Organisms
Land Organisms
Primary producers
(plants/phytoplankton)
Herbivores
(plant/phytoplankton eaters)
Carnivores
(herbivore eaters)
Have you or anyone you know ever eaten a land carnivore?
If so, what species was it?
Do you think its population could sustain the impact of humans eating it regularly? Why or why not?
List the species of marine carnivore that you or anyone you know has eaten.
5. Choose one of the following marine carnivores that is commercially fished along the west coast of the
United States.
Sardines: http://www.dfg.ca.gov/news/99001.html
Salmon: http://www.metrokc.gov/exec/esa/c2-DecliningSalmon.htm
Squid: http://www.sanctuaries.nos.noaa.gov/special/special.html
Summarize the historical and present state of this animal's population. You can make a verbal description,
draw a graph, or sketch a time line.
State three factors that control the size of this animal's population.
Would you recommend that humans continue to hunt and eat this species?
Year
-10000
-8000
-6500
-5000
-4000
-3000
-2000
-1000
-500
-400
-200
1
200
400
500
600
700
800
900
1000
1100
1200
1250
1300
1350
1400
1500
1600
1650
1700
1750
Human Population
1
5
5
5
7
14
27
50
100
162
150
170
190
190
190
200
207
220
226
254
301
360
400
360
443
350
425
545
470
600
629
1800
1850
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
2010
2020
2030
2040
2050
813
1,128
1,550
1,750
1,860
2,070
2,300
2,500
3,039
3,706
4,453
5,277
6,073
6,831
7,561
8,214
8,810
9,298