Having too many fish in a pond can limit the amount of food and space available. Predation
Or competition

competition

Explanation:

competition is to fight for the same resource. The fish are competing amongst each other for food in space.

its not predation because predation is when a population IS the resource

the calvin cycle has three stages. in stage 1, the enzyme rubisco incorporates carbon dioxide into an organic molecule. in stage 2, the organic molecule is reduced. in stage 3, rubp, the molecule that starts the cycle, is regenerated so that the cycle can continue

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.