Does intraspecific variation in the energy value of a prey species to its predators matter in studies of ecological energetics? A case study using insectivorous vertebrates

This study tested the assumption that variation in the energy value of different instars of a hemimetabolous insect makes no ecologically significant difference to rates of energy gain by its vertebrate predators and found it to be supported. Three mammal species, four bird species and a lizard species were used as predators and one grasshopper species as prey. Although instars of both male and female grasshoppers differed significantly in energy values, the energy returns to their predators based on these exact values were qualitatively similar to those produced when a commonly-used constant energy value of 23 J/mg dry weight was substituted. Regressions of specific energy returns on those based on the 23 J/mg constant were highly significant, so energy returns based on the constant were good predictors of those based on specific energy values. Although significant intraspecific variations in energy values occur in Acrida conica and probably in other hemimetabolous insects as well, the 23 J/mg dry weight constant appears adequate for most predation studies.