. Animal Ecology. Animal ecology. (Left) Ecological pyramids FIG. 13-8 classes (soil animals of tropical broe 1941); (b) dry biomass, Silver Sprint (c) per cent total metabolism by different tax (a) numbers by size .aved forest, Williams fream (Odum 1957a); _, of a hypotheti- cal soil population in a meadow (Macfayden 1957); (d) gross productivity, Lake Mendota (Lindeman 1942). 2702 5867/m2. Others Spiders Fly larvae Beetles i ri2 Springtails Fungi Protozoa Nemotodesr 16 1 Bacteria P 480 Sun 118,872 g-cal/cm2/yr a PYRAMID OF NUMBERS AND BIOMASS When the total animals in a comm
. Animal Ecology. Animal ecology. (Left) Ecological pyramids FIG. 13-8 classes (soil animals of tropical broe 1941); (b) dry biomass, Silver Sprint (c) per cent total metabolism by different tax (a) numbers by size .aved forest, Williams fream (Odum 1957a); _, of a hypotheti- cal soil population in a meadow (Macfayden 1957); (d) gross productivity, Lake Mendota (Lindeman 1942). 2702 5867/m2. Others Spiders Fly larvae Beetles i ri2 Springtails Fungi Protozoa Nemotodesr 16 1 Bacteria P 480 Sun 118,872 g-cal/cm2/yr a PYRAMID OF NUMBERS AND BIOMASS When the total animals in a community are grouped according to an arbitrary series of size ranges (Elton 1927, Allee et al. 1949), there are always a larger number of small individuals present than large ones. Plotting these data gives a pyramid of numbers. Pyramids of numbers arranged by trophic levels, rather than size, have special interest in respect to food coactions. In a bluegrass field, the number of green plants at the producer level (P) over 8 times the number of herbivorous invertebrates in the level of primary consumers (Ci) : the number of primary consumers was 2 times the number of spiders, ants, and predatory beetles at the secondary consumer level (C2) ; and the number of secondary consumers was over 100,000 times the number of birds and moles among the tertiary consumers (C3), because of the great difference in size of individual animals at these two levels (Odum 1959). In Michi- gan, the ratio between numbers of rodents and their hawk and owl predators was found to be approxi- mately 1000:1 (Craighead and Craighead 1956). In evaluating the importance of trophic levels in the community, biomass is a more important index than number of individuals. Of 13 ratios of fresh weights between different trophic levels (Lindeman 1941, Juday 1942, Turcek 1952, Birch and Clark 1953), the majority fall between 2:1 and 12 :1. These early studies furnish no certain evidence that the ratio varies betwe
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