The Evolution of Stability in Marine Environments Natural Selection at the Level of the Ecosystem

Starting from the premise that oscillations are dangerous for any system and that violent oscillations may be lethal, this paper contrasts the highly stable production systems of tropical waters with the seasonal and longer-term oscillations of temperate and polar waters. The differences are climatically determined, and since the present glacial type of climate is young in the climatic history of the earth, the ecological systems of the higher latitudes are considered as immature and at a low level of adaptation. That they may be in process of evolution toward greater stability is suggested by a number of phenomena, such as the development of large, slow-respiring, slow-growing individuals, and the production of the young in many arctic invertebrates in mid-winter or late fall. These and other observed peculiarities of high latitude fauna tend to make the most efficient use of the available plant food and to spread the cropping pressure over as much of the year as possible. Oceanic birds are cited as examples in which stable populations have been achieved by evolution of lower breeding rates, and the phosphate and nitrate cycles in the upper layers of tropical seas are discussed. It is emphasized that selection here is operating at the level of the ecosystem; competition is between systems rather than between individuals or specific populations.