Nonequilibrium in communities - Nonequilibrium Ecology - page 40

Figure 2.7. Ritchie and Olff have developed a scaling law model to test for species
packing and have fitted data from some free-living animal and plant communities to
it, concluding that these communities, are indeed densily packed and largely
structured by interspecific competition. Predictions are shown in a, d and g:
(a) Predicted size ratios (larger/smaller) for species of adjacent size versus size of the
larger species. (d) Predicted number of species expected for communities versus
log(size). (g) Predicted number of species versus productivity, or log(mr). Tests of the
model are illustrated in b, c, e, f, h, i which show observed values for East African
herbivores and Minnesota plants. From Ritchie and Olff ( 1999 ). Reprinted by
permission of MacMillan Publishing Ltd., and the authors.
ratios and are therefore more loosely packed, whereas the largest species are
limited by the maximum patch size (Figure 2.7d ) ; t he re sh ou ld be a
unimodal distribution of species numbers versus productivity (Figure
2. 7g ). Serengeti (East African) mammalian herbivores and Minnesota
savanna plants were shown to conform to the first two patterns (Figure
2. 7b , c , e , f ). The third pattern, according to the authors, is the most
commonly observed pattern of species richness versus productivity, and
was found for the two groups tested as well (Figure 2.7h , i ) . R oh de ( 2001a )
has shown that the packing rules do not apply to metazoan ecto- and