Defense physiology- implications for prey trophic function and nutrient recycling

Background/Question/Methods

The physiological reaction of prey to predation involves allocating resources from production to support emergency functions. An example of such a reaction is an increase in maintenance respiration concomitant with higher carbohydrate and lower N demand. Such changes in prey energy and elemental budget should alter the role prey play in regulating the quality of detrital inputs to soils. Nutrient content of detritus is an important determinant of the way soil communities regulate ecosystem processes. Thus, the physiological reaction of prey to predation can potentially explicate changes in ecosystem functioning.

Results/Conclusions

First empirical examination using an old-field model food-chain of an herbivore grasshopper (prey) and a predatory spider, thus far, support this new conceptual framework. Grasshoppers stressed by spider predators prefer to eat more carbohydrates and have a higher body carbon-to-nitrogen ratio than do grasshoppers raised without spiders. This change in elemental content does not slow grasshopper decomposition but perturbs belowground community function, decelerating the subsequent decomposition of plant litter. This legacy effect of predation on soil community function appears to be regulated by the amount of herbivore protein entering the soil. Using a ¹³C pulse-chase experiment in the same model system, we found that carnivore presence enhanced initial carbon fixation by plants and slowed the relative rate of carbon loss via ecosystem respiration. These changes in carbon cycling led to 1.4-times more carbon storage in above-ground and below-ground plant biomass when carnivores were present compared to conditions with just herbivores.