In contrast to the physiologist, ecologist should be able to ask questions so that answers were fit not only for laboratory conditions, but ultimately contributed to the expansion of knowledge and of the natural habitat.
If such complex observations and experiments are conducted on a quantitative basis, this means a transition to the second plane of ecological research, namely, population ecology. The goal here is to study changes in population density of species in a particular area for several generations. Fluctuations in population size due to uneven and dependent on the type of organism, habitat, and time the number of endogenous and exogenous factors from the complex structure of relationships, so that they act as a whole. Of course, there also should begin with an examination of individual particle contacts before you can get an idea about the whole dynamics of the population of the species. Epidemiology of fungal parasites of cultivated plants perfectly described humane and insect Andrevarta and Burcham, but only two are particularly important in the budget nature of the organisms.
The third stage by biological studies of whole landscape forms for understanding the relationship, and dependency of the phenomena of life, as well as the participation of organisms in the circulation of substances on a large natural complexes. Explanation of coexistence and the occurrence of organisms are still not enough to understand "biocenotic order" in a particular landscape or its parts. It occurs primarily as a result of increasingly multilateral relations among individual species, not only because of the relationship between these species and nonliving environment. The most important features of this order are as follows: