The metaphysical theory that the external world is not physical but is in fact mental or psychical. The epistemological claim that reality is best explained in terms of psychic phenomena like minds, spirits, or ideas instead of in terms of matter. The ethical device of positing an action, person, political organization, or state of being that is free of all the imperfections that characterize actual actions, persons, political organizations and states of being.
The debate over whether the individual or the whole is primary: ethically, semantically, ontologically, or epistemologically. For instance, the ontological individualist claims that individual elements are independent and self-existent whereas for the holist they are interdependent and constituted by the qualities of others. The ontological individualist claims, and the holist denies, that all complex phenomena are reducible; for the holist some qualities only emerge at the level of the whole.
The study of the geographical distribution of plants and animals on islands or in isolated locales (“habitat islands”). According to the equilibrium theory of island biogeography, species richness on an island stems from a balance between the number of species added by immigration and the number lost to extirpation. First proposed Edward O. Wilson and Robert H. MacArthur in 1963, the theory is increasingly important to conservation efforts—the creation of habitat islands represents one of the chief threats to biodiversity.