If you meant to add a page, you didn't. You might need to re post the question.
The answer to that is sunlight. If you need an explanation tell me but I think it’s self explanatory :)
Answer:
A stream channel is the physical confine of a stream consisting of a bed and stream banks. Stream channel development is controlled by both the water and sediment movement.
Traits controlled by genes can only be acted upon natural selection because they have to helpful to the survival of that organism.
