Its a one of 2 types of creature's faction have benefited from living together. If a deficiency is unable to sustain life, such as lichen, which is to be shared, and algae, etc.
The relationship of coexistence of two kinds of creatures, each partner to benefit from living together. If the party can not live like lichens, which are a combination of algae and fungi, and so on.
State one's relationship coexistence of life 2 type each benefit from living together. If the lack of any party will not be able to live, such as lichens.And so on.