Year 7 Science · Unit 1 · Lesson 15
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Learning Goals
Predict and reason
Read the scenario carefully, then answer both questions using ideas from this lesson.
Scenario
A marine reserve in NSW introduces 50 sea urchins into an area where a kelp forest had previously been destroyed by urchin overgrazing. Within 6 months, the urchin population has grown to 800 and the kelp forest has not recovered.
(a) Predict: What do you think will happen to the urchin population if the kelp forest continues to fail to recover? Write your prediction clearly.
(b) Justify: The 800 urchins are all competing for the same limited food supply. What type of competition is this — intraspecific or interspecific? Explain your reasoning using the correct scientific term.
Real-world scenario
Read the context below and answer both questions.
Real-world context
The snowshoe hare and Canadian lynx have been studied since the 1840s using Hudson's Bay Company fur trade records. Trappers recorded how many pelts they collected each year, giving scientists nearly 90 years of population data. When hare populations rise, lynx populations rise 1–2 years later. When hares crash, lynx numbers crash shortly after, with a similar delay.
(a) Sketch or describe in words what both populations would look like on a graph over 40 years. Label which line is the hare and which is the lynx, and indicate where the 1–2 year lag would appear.
(b) Explain why there is a lag of 1–2 years between hare numbers peaking and lynx numbers peaking. What biological process causes this delay?
1. A farmer notices that both sheep and rabbits are grazing in the same paddock. When rabbit numbers increase significantly, the sheep begin to lose weight. Identify the type of relationship between the sheep and rabbits, and explain what would happen to the sheep population if the rabbits continued to increase.
2. Mistletoe grows on a gum-tree branch and takes water and nutrients directly from the tree. The gum tree is weakened as a result. Using the correct term from the lesson, classify this relationship and explain your reasoning using the +/− notation.
Wrap Up
In one sentence, what was the main idea of this lesson?