. The Canadian field-naturalist. 16 The Canadian Field-Naturalist Vol. 92. AREA IN HECTARES (A) Figure 4. Number of species {S) plotted against the area (A) for the St. Lawrence River islands. Least squares regression curves of the power function of A are fitted. The solid line curves are based on all 18 areas; the broken line is the regression curve with number 10, Grenadier Island, excluded. The upper and lower curves correspond to the upper and lower A scales marked on the abcissa. The numbers are those given to the islands in Table I. Discussion Exploring these species-area relationships h
. The Canadian field-naturalist. 16 The Canadian Field-Naturalist Vol. 92. AREA IN HECTARES (A) Figure 4. Number of species {S) plotted against the area (A) for the St. Lawrence River islands. Least squares regression curves of the power function of A are fitted. The solid line curves are based on all 18 areas; the broken line is the regression curve with number 10, Grenadier Island, excluded. The upper and lower curves correspond to the upper and lower A scales marked on the abcissa. The numbers are those given to the islands in Table I. Discussion Exploring these species-area relationships has answered some questions and left others open to further study. The areas in the St. Lawrence Islands National Park in general form a homogeneous set of vascular plant associations. The one possible exception is Gordon Island, which is somewhat richer in number of species than would be predicted by its size. Our surveys were in no way biased towards species recording on Gordon Island and so it would be of particular interest to see whether this characteristic is borne out by data from other groups of organisms. Williams (1964) concluded empirically that the power function model (model 2) rarely applied in areas below about 1 km^ while the semi-log model (, species/log area) was the most appropriate for single associations ranging from a few square metres to hundreds of square kilometres. Kilburn (1966) has questioned this on the basis of observations on prairie and forest plots in Illinois and Wisconsin and of a re- examination of Hopkins' (1955) data from various communities in Britain. Both Hopkins' and Kilburn's data combined species numbers for vascular plants with those for various groups of non-vascular plants. By disentangling the species numbers in each taxonomic group (albeit speculatively) Kobayashi (1975) succeeded in obtaining a closer fit for these data to his modification of the semi-log model than that obtained by Hopkins (semi-log) or Kilburn (power functi
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