Predators can directly affect resources available to the microbial communities responsible for processes such as decomposition and mineralization. Predators regulate nutrient cycling by controlling the fate of prey nutrients through capturing and consuming prey, altering the transport and release of prey nutrients. Predators ingest prey tissue, discard inedible parts, assimilate some prey nutrients, eliminate metabolic wastes as excreta, and pass undigested food as egesta. Each foraging by-product differs in macronutrient composition, and their relative quantities are dictated by predator feeding strategy.
We compared two sit-and-wait predators with different feeding strategies: the white widow spider Lactrodectus pallidus digesting extra-orally, and the thistle mantid Blepharopsis mendica chewing prey piece by piece. Predators were fed Schistocerca gregaria grasshoppers and all by-products were collected after feeding events. Foraging by-products were then added to soil microcosms, followed by an addition of dry Stipa capensis grass to compare whether soil inputs affected the decomposition of plant matter as a result of changes in microbial community function. Soil carbon mineralization was measured by CO2 production and sampled until treatment tubes did not differ from control tubes.
Results/Conclusions
B. mendica mantids generated more excreta and egesta than L. pallidus spiders (47.03mg and 7.27mg respectively), and less prey remains (20.54mg and 36.59mg respectively). Similarly, foraging by-products differed in elemental and macronutrient composition. Prey carcasses directly added to soil had the highest rates of carbon mineralization, likely due to having the largest amount of biomass added to the soil. When adjusted for biomass, L. pallidus excreta and egesta had the highest rates of carbon mineralization per gram. However, when predator foraging by-products were pooled there was no difference in carbon mineralization between feeding strategies. These results suggest the form of prey-derived nutrients may be an important driver of nutrient cycling, but the overall effect is similar when considering all prey nutrients regardless of feeding strategy.