Why do you think there are rarely 5 or 6 links in a food chain? To help, think about how much food it took for all of your energy needs in your life. Imagine if an animal had to eat 10 humans a year to survive is this feasible... or there that much energy available?

Most food chains have no more than four or five links. There cannot be too many links in a single food chain because the animals at the end of the chain would not get enough food and energy to stay alive.

Explanation:

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).