群集係数による群集の層化について

抄録

1) Concerning a quantitative character of an animal community, the equilibrium among the species constituting it is expressed by MOTOMURA's law of geometrical progression in an animal community, which is written as logy=b_1-a(x-1), where y is the population density of each constituent species, x its order in magnitude, a and b_1 constants ; accordingly a and b_1 are indices for measuring the condition of this equilibrium. Moreover, a expresses the intensity of competition among species in the community, and b_1 is the logarithm of population density of the dominant species. 2) When a habitat is divided into several layers or quadrats, a quantitative relation among the layers can, in connection with each layer, be measured by the communality, h^2,induced from the matrix of correlation coefficients among the population densities of the species constituting the community in each layer by means of the method of factorial analysis. 3) Number of species in each layer is mainly related to a and b_1,and a numeral relation of the common species between layers is measured by the coefficient of closeness, p. As it is empirically proved that p is in a simple functional relation connected with d, which is the distance between the points given by sets of coefficients of the common factors induced from the matrix of correlation coefficients among the population densities of the constituent species, then the factors concerning the number of total species and of common species are contained within the facts of the above 1) and 2). 4) From the above facts it is recognized that a great part or quantitative characters in a community is measurable by the three indices, a, b_1,and h. Putting K to one of these indices, K to its mean value, n to the number of layers, σ^2_K=Σ(K-K)^2/n, and t=(K-K^^-)/σ_K, from the values of t for a, b_1 and h, the community coefficient, R, has been defined as follows : [numerical formula] and it signifies an ecological value representing a community of each layer. 5) R has been tested in practice with the Ostrea spinosa-community observed by MOTOMURA and the plankton community in a small pond observed by HAMAI and OSAWA, and good results have been obtained.