Grinnell's earlier definition emphasising states of the environment suitable for the species. Others have argued there are more similarities than differences between the two versions of the niche concept. After the Second World War, Elton became much more concerned with the impact of invasive species on natural ecosystems. His 1958 book The Ecology of Invasions by Animals and Plants founded invasion ecology as a separate sub-discipline. This book became the basis of the study of biological invasions. It was the first of its kind to warn about the harmful effects and damages invasive species can have on an ecosystem. The first part of the book focuses on the invader species and their mode of transport into the new environment. The second part of the book focuses on the struggle between invasive species and the indigenous, though some invaders enter habitats with no prior species filling their specific niche. The final part of The Ecology of Invasions by Animals and Plants deals with the issue of conservation and its importance to maintain species diversity. Bibliography Animal Ecology, 1st ed., 1927, Sidgwick and Jackson, London. Reprinted several times, e. g. 2001, The University of Chicago Press, . 2nd ed., The Ecology of Animals, 1946, London: Methuen Voles, Mice and Lemmings: Problems in population dynamics 1st ed., 1942. Oxford: Clarendon Press. Facsimile reprint, 1969, New York: Wheldon & Wesley Ltd. The Ecology of Invasions by Animals and Plants, 1958, Methuen, London. Reprint, 2000, The University of Chicago Press. The Pattern of Animal Communities, 1st ed., 1966, London: Methuen. 2nd ed., 1979, London: Chapman & Hall References External links Charles Sutherland Elton – English Ecologist Elton's Ecologists: A History of the Bureau of Animal Population Fifty years of invasion ecology – the legacy of Charles Elton, Symposium 12–14 November 2008, hosted by DST-NRF Centre of Excellence for Invasion Biology, Stellenbosch University, South Africa. 1900 births 1991 deaths Scientists from Manchester Alumni of the University of Liverpool Alumni of New College, Oxford English ecologists 20th-century British zoologists Fellows of Corpus Christi College, Oxford Fellows of the Royal Society Population ecology People educated at Liverpool College