Effects of prey nutrient content on spider excreta content and soil-carbon mineralization rates

Abstract

Recent work suggests that predators can play a fundamental role in cycling nutrients throughout ecosystems. Through consumer-driven effects, including depositing excreta and uneaten parts of prey carcasses, predators can influence ecosystem function by altering the amount and type of nutrients available to soil communities and primary producers. In this study, I examined how different prey fed to a spider affected the forms and concentrations of nutrients deposited, and their subsequent effects on ecosystem function (soil-carbon mineralization rates). More specifically I examined: 1) The differences in elemental concentrations of prey remains and spider excreta when spiders fed on different species of prey (caterpillars, cockroaches, crickets, and flies). 2) If the concentrations of elements deposited by spiders differ between spring and fall. 3) The effects of spider excreta from different predator-prey interactions on soil-carbon mineralization rates. Overall, spider excreta generally had higher concentrations of many elements compared to prey remains, and whole prey. Additionally, elemental concentrations in whole prey and remains exhibited significant variation among prey species, while spider excreta had the lowest variation. Seasonally, there were significant differences in the concentrations of elements deposited between fall and spring excreta. Finally, soil-carbon mineralization rates were higher in controls than in soil with excreta from spiders fed caterpillars, cockroaches, and flies, with crickets being intermediate. The results from this study highlight the complex interactions between predator and prey physiology that determine the concentrations of elements deposited following predation. A better understanding of how other predatory-prey interactions impact nutrient feedbacks will be critical to disentangle specific consumer-driven effects on ecosystem function.