Trophic structure, available resources and population density in terrestrial vs. aquatic ecosystems.

Abstract The relationship between available resources and the level at which density is regulated may not be obvious where direct inter- or intraspecific competition for available resources is absent. Interpretation of such cases requires that a distinction be made between organisms ingesting living material (biophages) and those subsisting on dead organic matter (saprophages). A modified trophic model incorporating this distinction is used to develop a hypothesis explaining how mean densities of first-order biophagus organisms are determined in accordance with life history characteristics of autotrophs in the system. Mean biophage densities will be held at low levels where effects of escape from control would be most damaging to a system, i.e. where the biotic potential of first-order biophages is much higher than that of the autotrophs. The hypothesis accounts for density levels and regulatory mechanisms differing with trophic levels and helps to explain the prevalance of well-developed three-level trophic communities in terrestrial ecosystems and four-level communities in aquatic systems.

[1]  R. Wiegert.  Thermodynamic considerations in animal nutrition. , 1968, American zoologist.

[2]  J. R. Bray.  Primary Consumption in Three Forest Canopies , 1964 .

[3]  L. Slobodkin,et al.  Community Structure, Population Control, and Competition , 1960, The American Naturalist.

[4]  Paul R. Ehrlich,et al.  The "Balance of Nature" and "Population Control" , 1967, The American Naturalist.

[5]  H. Lamprey.  ESTIMATION OF THE LARGE MAMMAL DENSITIES, BIOMASS AND ENERGY EXCHANGE IN THE TARANGIRE GAME RESERVE AND THE MASAI STEPPE IN TANGANYIKA , 1964 .

[6]  A. Milne.  On a theory of natural control of insect population , 1962 .

[7]  M. Engelmann.  The Role of Soil Arthropods in the Energetics of an Old Field Community , 1961 .

[8]  B. C. Patten.  An Introduction to the Cybernetics of the Ecosystem: The Trophic‐Dynamic Aspect , 1959 .

[9]  L. Slobodkin,et al.  Regulation in Terrestrial Ecosystems, and the Implied Balance of Nature , 1967, The American Naturalist.

[10]  J. Teal.  Energy Flow in the Salt Marsh Ecosystem of Georgia , 1962 .

[11]  G. Petrides,et al.  Population Densities and the Range-Carrying Capacity for Large Mammals in Queen Elizabeth National Park, Uganda , 1965 .

[12]  Raymond L. Lindeman.  The trophic-dynamic aspect of ecology , 1942 .

[13]  E. Odum,et al.  Population Energy Flow of Three Primary Consumer Components of Old‐Field Ecosystems , 1962 .

[14]  D. Pimentel.  Population regulation and genetic feedback. Evolution provides foundation for control of herbivore, parasite, and predator numbers in nature. , 1968, Science.

[15]  J. Phillipson,et al.  Secondary Productivity of Terrestrial Ecosystems , 1970 .

[16]  M. Engelmann.  Energetics, Terrestrial Field Studies, and Animal Productivity , 1966 .

[17]  William W. Murdoch,et al.  "Community Structure, Population Control, and Competition"-A Critique , 1966, The American Naturalist.

[18]  A. Macfadyen.  Metabolism of soil invertebrates in relation to soil fertility , 1961 .