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
Email: streamdoctor@aol.com
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 streamdoctor@aol.com.
Originally published June 14th, 2004 on Fly Anglers Online by Robert Younghanz.