When one species occupy an area leading to declining or disappearance of other species; this changes in composition of species in any given area is called ecological succession. When succession occurs in an area where no living organism ever existed; it is called Primary Succession. There has to be soil for a biotic community to be established and it takes a hundred to thousand years for fertile soil to be produced hence, primary succession take is a slow process. Hydrarch succession taking place in water as well as xeric conditions taking place in dry areas, both proceed to mesic conditions that are neither too dry nor wet. Saprophytes though play a vital role, of degrading dead matter, in an ecosystem are not given any place in an ecological pyramid.