Question

the case of intolerance occurs when a population is stressed (in this case, river trout). too much or too little of any water - quality parameter (graph below) can lead to it.
dissolved oxygen (mg/l) number of fish counted
0 0
1 0
2 0
3 2
4 3
5 3
6 5
7 8
8 11
9 15
10 18
11 22
12 24
13 23
14 20
15 18
16 15
17 12
18 10
19 6
20 3
21 1
22 0
conclusion

1. label the optimal range, zones of physiologic stress, and zones of intolerance on the graph above.
2. biological indicator species are those whose overall health and population numbers can offer a signal of the overall health of an ecosystem. explain why fish, specifically steelhead trout, would be an effective indicator species.

Explanation:

1. The optimal range is where the number of fish is highest, typically around 10 - 11 mg/L dissolved oxygen. Zones of physiological stress are where the number of fish starts to decline from the peak, say 8 - 9 mg/L and 12 - 13 mg/L. Zones of intolerance are at the extremes where few or no fish are present, like below 3 mg/L and above 18 mg/L.
2. Steelhead trout are effective indicator species because they are sensitive to changes in water quality such as dissolved - oxygen levels. Their presence or absence, as well as population size, can reflect the overall health of the aquatic ecosystem. They are also a key part of the food web and their health can be an early warning sign of ecosystem problems.

Answer:

1. Optimal range: 10 - 11 mg/L dissolved oxygen; Zones of physiological stress: 8 - 9 mg/L and 12 - 13 mg/L; Zones of intolerance: below 3 mg/L and above 18 mg/L.
2. Steelhead trout are sensitive to water - quality changes like dissolved - oxygen levels, are part of the food web, and their health can signal ecosystem problems.