I am interested in the effects of day length ie the number o

I am interested in the effects of day length (i.e. the number of hours of sunlight) on the predation rates of juvenile salmon upon their prey in streams. I test the rates in streams of equal sizes with equally sized fish early in the spring, in the middle of summer, and again in fall and find that both the total food intake over the whole day and the intake per hour of daylight is highest in mid-summer. Can I say with some confidence that day length affects predation rates in salmon? Why or why not?

Solution

No, we can\'t say that the light is the only factor determining the predation rate of salmon. As the no of prey for salmon can also matter which is present in the stream which can change due to the presence of the light.

So for designing this experiment we have to also take consideration the growth of the prey depending on the light..!! Or the amount of prey should also be same..!!