PARASITE ABUNDANCE, BODY-SIZE, LIFE-HISTORIES, AND THE ENERGETIC EQUIVALENCE RULE

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.