Abstract
Insectivores gain macronutrients and elements from consuming arthropod
prey, but must also deal with indigestible components (i.e.,
exoskeleton) of prey. For example, avian chicks (e.g. northern
bobwhites; Colinus virginianus) have limited gut space, and ingesting
prey with relatively higher proportions of indigestible components may
impact assimilation efficiency, growth, and survival. The ability of
insectivores to choose higher quality prey would depend on prey taxa
varying consistently in nutritional content. We tested if there were
consistent differences among taxonomic orders of arthropod prey in their
macronutrient (protein and lipid), elemental (C and N), and exoskeleton
content. We used northern bobwhite chicks as our focal insectivore and
focused on their potential prey as a case study. We also tested the
influence of indigestible exoskeleton on the measurement of
macronutrient content and the ability of elemental content to predict
macronutrients. We found large and consistent variation in macronutrient
and elemental content within and between arthropod orders. Some orders
had consistently high protein content and low exoskeleton content (i.e.,
Araneae) and are likely higher quality prey for insectivores. Abundant
orders common in the diets of insectivores, like Hymenoptera and
Coleoptera, had high exoskeleton content and low protein content. We
also found support for the ability of elements to predict
macronutrients, and found that metabolizable (i.e. exoskeleton removed)
elemental content better predicted macronutrient content. A better
understanding of arthropod nutrient content is critical for elucidating
the role of spatial and temporal variation in prey communities in
shaping the growth and survival of insectivores.