Each living organism in nature lives is not isolated, it is surrounded by many other representatives of wildlife, and all of them interact with each other. Interactions between organisms and also influence them on living conditions represent set of biotic factors of the environment - a neytralizm.
The ecosystem is a necessary condition of existence of living beings. Stocks of biogenous elements are not boundless, and only the system of circulation can give to these stocks property of infinity which is necessary for continuation of life. Living organisms settle not accidentally with each other, and form communities which are adapted for joint dwelling. It is possible to distinguish certain types of the relations which have much in common at organisms of various systematic groups from all huge variety of all interrelations of living beings. How they affect an organism, all groups can be divided into negative, positive and neutral. It is possible to distinguish the following types of the relations from all huge variety of an interconnection of living beings: symbiosis, neytralizm, antibiosis. Neytralizm is a form of relationship where 2 populations do not influence life at each other, but forming a biocenosis (community or group of organisms which in common inhabit some certain area of land or a reservoir) they depend on a condition of this community in general.
For example, elks and squirrels, live in one forest, but do not contact among themselves, however the condition of the habitat (wood) affects them. Other example: there are several types of the American slavka - it is small insectivorous birds who live in fir forests. All of them get food in crowns. But, it appears, each look uses mainly what - that one certain part of krone: someone top, other look thin branches, etc. Each look occupied the niche, performs the certain function and birds do not influence each other life, but they depend on a condition of trees where get to themselves food. Of course, such stable relations developed as a result of mutual adaptation. In the nature the clean neytralizm meets very seldom because between types indirect relationship is possible. It is considered that types which form one community have to be in different ecological niches. However the hypothesis was made recently that the form of relationship, such as neytralizm was formed thanks to ecological similarity of types.