Please see the slidedeck for the lesson – 4 – A – Complex Ecosystems and Terrestrial Systems.pptx

Relationship Types

Watch the following videos and answer the questions that pertains to each video. 

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

Questions

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.
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?