DOES INTRASPECIFIC VARIATION IN THE ENERGY VALUE OF A PREY SPECIES TOITS 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 si gnificant difference to rates of energy gain by its vertebrate predato rs and found it to be supported. Three mammal species, four bird speci es and a lizard species were used as predators and one grasshopper spe cies as prey. Although instars of both male and female grasshoppers di ffered significantly in energy values, the energy returns to their pre dators based on these exact values were qualitatively similar to those produced when a commonly-used constant energy value of 23 J/mg dry we ight was substituted. Regressions of specific energy returns on those based on the 23 J/mg constant were highly significant, so energy retur ns based on the constant were good predictors of those based on specif ic energy values. Although significant intraspecific variations in ene rgy 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.