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.