Living things in a habitat depend on one another. They also depend on resources. These include food, water, light and space. Resources are limited. So organ...
Question 1 Report
Living things in a habitat depend on one another. They also depend on resources. These include food, water, light and space. Resources are limited. So organisms must compete for them. This competition helps to control population sizes. Predators and prey also affect each other. A change in one changes the other. For example, the number of rabbits in a field may rise. The foxes that eat them then find more food. So the number of foxes may rise too. A student studied predators and prey in a habitat. They were asked how the two are linked.
(a) State what is meant by the term competition. [1]
(b) State three resources that plants in a habitat may compete with one another for. [3]
(c) Explain how an increase in the number of rabbits could lead to an increase in the number of foxes. [2]
(d) Explain how the increase in the number of foxes could then cause the number of rabbits to fall again. [3]
(e) Suggest one other factor, apart from predators, that could limit the size of the rabbit population. [1]
Answer Details
This question is about competition for resources and predator-prey links. The rabbit-fox cycle is the key idea: prey numbers drive predator numbers, and predators then push prey numbers back down.
(a) Competition is the struggle between organisms for the same limited resources [1].
(b) Any three resources that plants compete for (max 3) [3]: light; water; mineral ions / nutrients; space. (Plants do not compete for food, since they make their own.)
(c) More rabbits means more food for the foxes [1]; so more foxes survive and reproduce, and their numbers increase [1].
(d) The larger number of foxes eats more rabbits [1]; so more rabbits are killed than are replaced by breeding [1]; and the number of rabbits then falls again [1]. This is why the two populations rise and fall in a linked cycle.
(e) Any one other limiting factor [1]: a shortage of food / grass; disease; or lack of space.
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