Nonequilibrium in communities - Nonequilibrium Ecology - page 39

Figure 2.6 A. Number of species of metazoan ectoparasites on the heads and gills per
species of marine teleost (5666 fish of 112 species). Note: maximumnumber 27 parasite
species, most species with fewer than seven. If 27 is considered to be the maximum
possible on all fish species, the percentage of empty niches would be 84.1%.
B. Abundance ( ¼ mean number of metazoan ectoparasites of all species per host
species). Note: maximum abundance more than 3000, but most species with fewer
than five. From Rohde ( 1998a ). Reprinted by permission of the editor of Oikos.
Ritchie and Olff ( 1999 ) have proposed a new method to examine the
problem of species packing. They used spatial scaling laws (fractal geo-
metry) to derive a rule for the minimum similarity in the size of species
that share resources, proceeding from the recognition that larger species
detect only the larger patches of food but can tolerate lower resource
concentrations than smaller species. The rule permits several predictions:
(1) the body-size ratio of species of adjacent size should decline with
increasing size of organism, because smaller patches richer in resources
used by smaller species occupy relatively less volume than the larger but
poorer patches used by larger species (Figure 2.7a ); (2) there should be
a unimodal distribution skewed to the left, when species numbers are
plotted against the size of species, because smaller species have larger size