A fishing lake has a population of carp…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A fishing lake has a population of carp. Its age pyramid has a very narrow base, a broad middle and a wide top. Anglers catch mostly large old fish.
- What shape is this pyramid, and what kind of population does it show?
- What will happen to the population if nothing changes?
- The lake is stocked every year with a large number of young carp. How does the pyramid change?
- Why does a pyramid with a large pre-reproductive group predict growth?
Need a reminder? The key ideaShow
The sex ratio is the number of females for every males, . An age pyramid has a pre-reproductive, a reproductive and a post-reproductive group. A triangle means expanding, a bell means stable and an urn means declining.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) An urn shape, with a narrow base. The population is declining.
Step 2. (b) Few young fish will replace the old ones, so the number will fall.
Step 3. (c) The base becomes wider. The pre-reproductive group grows, and the pyramid changes towards a bell or a triangle.
Step 4. (d) The young ones will reach the reproductive age. Then there will be more breeding adults, and more births.
Answer: (a) urn, declining; (b) it falls; (c) the base widens; (d) the young become the next breeders.
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