e so many kinds of animals?Am. Nat. 93,145-159 (1959). 2. Elton, C. S. Me Ecabgy of Invasions by Animals and Plants (Methuen, 1958). 3. MacArthur, R. H. Fluctuationsof animal populations. and a measure of community stability. Ecology 36, 533-536 (1955). 4. May. R. M. Will a large complex system be stable? Nature 2