THOSE TWO QUESTIONS PLS^

1: if the species health is low it will affect everyone in the habitat as well as how the habitat functions, because the species will not be behaving as normal and might not care for the habitat.

2: all the fish  in the stream can adapt a genetic protection against diseases due to the different types of adaptions and DNA structures, the fish mating will produce stronger fishes who can live through different types of disease

Explanation:

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.