Well-known proponents of pathocentrism include, i.a.:

Regan, T. (1983): The Case for Animal Rights. London: Routledge and Kegan Paul. 

Singer, P. (1975): Animal Liberation. New York: Random House. 

A good general overview of the various approaches in environmental ethics can be found in, for example:

Krebs, A. (ed.): Naturethik. Grundtexte der gegenwärtigen tier- und ökoethischen Diskussion. 8th ed. Frankfurt a. M.: Suhrkamp. (German)

Krebs, A. (1999): Ethics of Nature. A Map. Berlin/New York: Walter de Gruyter.