Why do you think that parasitism exists, when one of the organisms is harmed by the relationship?

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.

feral cats are estimated to eat tens of millions of native animals each night in australia