The diagram below shows a food web.
a) Use the food web to draw a food chain that has four trophic levels.
b) All the frogs in the food web die of a disease. Explain what will happen to the size of the population of snails.
Important Questions on Ecology
The graph shows how the estimated population of snowshoe hares and lynx in one part of Canada changed over 20 years.
| Year | 1916 | 1917 | 1918 | 1919 | 1920 |
| Estimated number of snowshoe hares (in thousand) | 28 | 16 | 9 | 12 | 5 |
a) Use the data shown in the table to finish plotting the line for the snowshoe hares.
b) Describe how the population of Lynx changed between 1913 and 1917.
c) When the snowshoe hare population increased, the Lynx population also started to increase. Explain why.
Anastasia studies water pollution. She uses indicator species to find out how polluted the water is at two different sites in a town.
| Species | Sensitivity to pollution |
| Stonefly larva | Cannot live in polluted water |
| Alderfly larva | Cannot live in polluted water |
| Freshwater mussel | Can live in slightly polluted water |
| Damselfly larva | Can live in slightly polluted water |
| Bloodworm | Can live in polluted water |
| Rat-tailed maggot | Can live in polluted water |
| Sample site | Species found |
| A | Alderfly larva, stonefly larva, freshwater mussel |
| B | Rat-tailed maggot, bloodworm |
Which sample came from polluted pond?
