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Ecological Relationships 1
Ecological Relationships
What symbiotic relationships are seen in ecosystems?
Why?
All living organisms need each other in some way to survive. This can include the interactions between predators and their prey, the close associations between and among living things ( symbiosis ), or the com- petitive relationships between and among species. All of these relationships may be equally advantageous to the parties involved, or they may be more beneficial to one organism over the other.
Model 1 – Predator–Prey Relationships
Relationship between Snowshoe Hares and Lynx
Number of hares Number of lynx
Year
Number of hares × (
3 ) Number of lynx × (
(^) ) 3
180
160
140
120
100
80
60
40
20
0
6
4
2
1845 1850 1855 1860 1865 1870 1875 1880 1885 1890 1895 1900 1905 1910 1915 1920 1925 1930 1935
- Refer to the graph in Model 1.
a. What does the y axis on the left represent?
b. What does the y axis on the right represent?
c. For both y axes, what value do the numbers on the axes need to be multiplied by?
- What was the approximate population of snowshoe hares in 1865?
Name: _____________________________________ Period: _____
2 POGIL™^ Activities for High School Biology
- What was the approximate population of lynx in 1865?
- When the number of snowshoe hares is high, what happens to the number of lynx? Use actual data from the graph to support your observation.
- What happens to the population of lynx as the number of snowshoe hares decreases? Use actual data from the graph to support your observation.
- Propose an explanation for the apparent cause and effect relationship between the populations of lynx and hares.
- What does this information tell you
a. about the effect of size of prey populations on the number of predators?
b. about the effect of predators on the populations of their prey?
- What other factor would infl uence the size of the hare population in addition to the size of the population of lynx?
4 POGIL™^ Activities for High School Biology
- Refer to the fungus and algae relationship in Model 2.
a. Is there a benefi t for one of the organisms or for both?
b. Is either the fungus or the algae harmed by this relationship?
c. Which other relationship in Model 2 is similar to that between the fungus and the algae?
- Refer to the shark and remora relationship in Model 2.
a. In the shark and remora relationship, is there a benefi t for one of the organisms or for both?
b. Is either the shark or the remora harmed by this relationship?
c. Which other relationship in Model 2 is similar to that between the shark and the remora?
Read This!
Symbiotic relationships are identifi ed by how they affect the organisms involved. The three types of sym- biotic relationships are listed below.
- Mutualism: Both organisms benefi t from the relationship.
- Parasitism: One organism benefi ts and the other is harmed.
- Commensalism: One organism benefi ts and there is no effect on the other.
- Using the information from the Read This! box, label each of the relationships in Model 2 as mutualism, parasitism or commensalism.
- With your group, choose one of the organism pairs from Model 2 and justify why you catego- rized the relationship as you did.
Ecological Relationships 5
Model 3 – Inter- and Intra-specific Competition
Graph A Graph B
Graph C
P. aurelia
P. aurelia and P. caudatum grown separately
P. coudatum
Number of Days
0
Time (weeks)
Mean Body Mass (g)
Rate of growth of R. tigrina tadpoles in populations of different sizes.
0 1 2 3 4 5 6 7 8 9 10
20
Relative Population Size
P. aurelia
P. aurelia and P. caudatum grown together
P. coudatum
Number of Days
0 20
Relative Population Size
Minimum mass needed for metamorphosis to occur.
5 individuals 40 individuals 60 individuals 160 individuals
- What are the names of the species in graphs A and B in Model 3?
- Which graph shows competition between two different species?
- Which graph in Model 3 shows population growth for only one species?
- What is the difference between the growing conditions in graph A and graph B?
Ecological Relationships 7
- Propose an explanation for why the population size affects the number of weeks before metamor- phosis of the tadpoles occurs.
- The type of competition represented by graph C is referred to as intraspecifi c competition. What is different about this compared to the competition seen in graph B?
8 POGIL™^ Activities for High School Biology
Extension Question
- An investigation was carried out into competition between two species of grass, Bromus madri- tensis and B. rigidus. Equal numbers of seeds of B. madritensis were sown in a number of different pots. In each pot, an equal number of seeds of B. rigidus was then sown a different number of days after B. madritensis. The results are shown in the graph below.
Given that the total dry mass of plant material was the same in each pot, summarize the main conclusions that can be drawn from this investigation. Suggest an explanation for the results when the delay before sowing B. rigidus was 30 days.
100
80
60
40
20
0 0 10 20 30
Percentage contribution of B. madritensis to total dry mass after 45 days
Delay before planting B. madritensis /days
