The Stream Doctor

June 14th, 2004

Email YOUR Questions directly to the Stream Doctor. This is your opportunity to get an experts professional opinion on anything stream related.

Q. I read your article about the various types of macroinvertabrates found in a trout stream. I attended a conservation camp over the summer and from what I remember we were taught that the various types of shredders, grazers, etc. were to be found at different gradients in the stream. This does not make sense to me because it would seem that if there were leaves falling in one area, then the type of insect that could utilize this food source would be present in that area, regardless of the gradient. Is this correct?

A. You're absolutely correct, gradient has nothing to do with the type of functional groups present; it is related to the available food resources. Having said this, there is a related factor that your instructors may have mixed in. This is the fact that most CPOM, and thus shredders, are usually found in the small headwater reaches of streams which also happens to be the region where gradients are usually higher. At the same time, grazers are most abundant where adequate sunlight reaches the stream bed so that algae can grow, and this usually occurs in the mid-reaches of streams where the gradient is usually less than in the headwaters. This is coincidence; gradient is not the determining factor - the food resources are. All of this emphasizes the fact that the insect communities found at a certain location in a stream are the result of many interacting factors; thus, care should be taken when attributing something to any one factor.

If you have a question, please feel free to contact me.
~ C. E. (Bert) Cushing, aka Streamdoctor
105 W. Cherokee Dr.
Estes Park, CO 80517
Phone: 970-577-1584

The 'Stream Doctor' is a retired professional stream ecologist and author, now living in the West and spending way too much time fly-fishing. You are invited to submit questions relating to anything stream related directly to him for use in this Q & A Feature at

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