What is the Law of Tolerance?
There is a limit for everything.
The biological structure of a community is first constrained by the environmental tolerances of the species. It is called as fundamental niche. These tolerances are in turn modified through direct and non-direct interactions with other species since there is not only one species living in the environment. It is called as realized niche. Competitor species and predator species can restrict a species from a community. However, mutual species can facilitate a species' presence and population within the community.
Abiotic environment (nonliving features, such as temperature, physical conditions, climate, etc.) will alter these constraints on distribution of species and their populations. Species differ in their range of environmental tolerances.
Reference: Smith, T.M. and Smith, R.L. (2009) Elements of Ecology. Pearson International Education. San Francisco, CA, USA.