Relationship Types

Watch the following videos and answer the questions that pertains to each video.  Submit your answers to the Teams dropbox.  Once submitted use the answer key to assess your work, tally marks earned and resubmit corrected file.

Shark and Turtles

1. How does the turtle protect itself?

2. What relationship is held between the tiger shark and the loggerhead turtle

Unlikely Travel Companions

3. List three ways in which being near a shark might be beneficial to a fish.

4. What is one way that a shark might benefit from a fish (other than as prey)?

5. Classify each shark-fish relationship shown in this video segment as commensalism, mutualism or parasitism.

Collapse of the Sharks

6. Why are shark populations in danger of collapse?

7. How has the relationship between sharks and humans changed over time?

8. What might happen if the shark fin trade continues unchecked?

Sharks in the Future

9. Describe the type of tourism seen in this clip.

10. What benefit do these businesses provide to: sharks? To local populations? To tourists?

11. How might these businesses help prevent the collapse of shark populations?

Case Study: Investigating a Predator – Prey Relationship

Case Study: Do Moose Need Wolves?

Graph paper to download (If you have a printer and want to do it by hand!)

Here is a more recent set of data on prey-predator relationships for you to analyse.  The moose population on an island sanctuary was about 1000 animals in 1974.  The 300km2 island was characterised by dense areas of spruce forest and bogs.  There were no natural predators of the moose.   Wildlife managers thought the growing moose populations would eventually become too large, outgrowing the carrying capacity of its ecosystem.  Already a number of moose were dying each year from a combination of winter exposure and starvation.  Other factors could be involved as well.

The managers decided that the moose population must be controlled, so it would not overshoot the carrying capacity and end up crashing.  In 1975 they decided to fly in 10 wolves.  Wolves are natural predators of moose.  Wolves are best described as opportunistic feeders.  That is, they will prey on whatever the opportunity provides.  Often this means that the wolves kill the weakest individuals, such as the old, diseased and the very young.  Such moose are the easiest to get.  Although wolves also capture some stronger moose, a healthy moose in its prime can usually fend off its attackers.  Therefore wolves can help to strengthen the herd of moose as well as control its numbers.  The results of this natural predation program were shown in Table One.


Table One: Wolf and Moose Populations Changes on an Island Sanctuary

Year Wolf Population Moose Population Moose Offspring Predation Starvation and Winter Kills Population Change (moose)
1975 10 1132 478 223 97 +158
1976 13 1290 543 304 148 +91
1977 17 1381 690 384 267 +39
1978 23 1420 736 453 269 +14
1979 27 1434 754 596 271 -113
1980 30 1321 663 628 746 39
1981 30 1321 663 628 101 -66
1982 33 1255 620 746 39 -165
1983 25 1090 526 543 3 -20
1984 21 1070 535 487 0 +48
1985 21 1118 549 498 0 +51


  1. Graph the changes in the wolf and moose populations for the nine year study period. Plot time on the x-axis and the population numbers on the y axis (use different colours for each population).  You can use a graph that has two y axis as the wolf and moose population values are very different.Graph tip - How do I make a second Y axis and assign particular data sets  to it? - FAQ 210 - GraphPad
  2. What would likely have happened to the moose population if a few more wolves had been introduced in 1975? Would this have been better for the ecosystem?
  3. Why did the wolf population decrease after 1981?
  4. In which year was the moose mortality rate due to starvation and winter exposure the highest? Using you data and knowledge of ecology why so many died.
  5. Assume hunters were allowed to kill half the wolf population in 1980. There would only be 15 wolves let.  Predict what might have happened to the moose population as a result.
  6. Is wolf predation on this island effective at limiting moose populations? List 3 others factors which could limit the numbers.
  7. How did the size of the moose population influence the numbers of wolves on the island? What other natural factors would limit the wolf population?
  8. You should notice a time lag between population changes of wolves and moose in your graph. This is what usually happens between predators and prey.  Suggest why such a time lag occurs.
  9. To maintain a healthy prey population, the predator-prey ratio is of great importance. Explain this statement.
  10. Could hunting have been used, alone or with wolf predation, to achieve a stable moose population?

Submit to the Teams Dropbox.