P. Ameberg et al., PARASITE ABUNDANCE, BODY-SIZE, LIFE-HISTORIES, AND THE ENERGETIC EQUIVALENCE RULE, The American naturalist, 151(6), 1998, pp. 497-513
If common processes generate size-abundance relationships among all an
imals, then similar patterns should be observed across groups with dif
ferent ecologies, such as parasites and free-living animals. We studie
d relationships among body size. life-history traits, and population i
ntensity (density in infected hosts) among nematodes parasitizing mamm
als. Parasite size and intensity were negatively correlated independen
tly of all other parasite and host factors considered and regardless o
f type of analyses (i.e., nonphylogenetic or phylogenetically based st
atistical analyses, and across or within communities). No other nemato
de Life-history traits had independent effects on intensity. Slopes of
size-intensity relationships were consistently shallow, around -0.20
on log-log scale, and thus inconsistent with the energetic equivalence
rule. Within communities, slopes converged toward this global value a
s size range increased. A summary of published values suggests similar
convergence toward a global value around -0.75 among free-living anim
als. Steeper slopes of size-abundance relationships among free-living
animals could be related to fundamental differences in ecologies betwe
en parasites and free-living animals, although such generalizations re
quire reexamination of size-abundance relationships among free-living
animals with regard to confounding factors, in particular by use of ph
ylogenetically based statistical methods. In any case, our analyses ca
ution against simple generalizations about patterns of animal abundanc
e.