Experimental Exclusion of Insectivorous Predators Results in No Responses Across Multiple Trophic Levels in a Water-Limited, Sagebrush-Steppe Ecosystem

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Predators can have strong influences on ecological processes through impacts on individuals at lower trophic levels, and changes in predator-prey dynamics can alter ecosystem functioning. However, much of what we currently know about interactions across trophic levels comes from mesic or relatively fertile systems, with fewer studies examining trophic interactions and resulting ecosystem processes in arid or infertile systems. To address this knowledge gap, we excluded avian predators from shrubs during the growing season using netting in a sagebrush steppe environment. We compared arthropod abundance, shrub herbivory damage, physiology (gas exchange and chlorophyll fluorescence), litter chemistry (C/N ratios and concentrations of phenolic compounds) and decomposition between netted and un-netted (control) sagebrush (Artemisia tridentata ssp. wyomingensis) shrubs across a growing season. While there were clear seasonal patterns in measurements, we observed no statistically significant differences between netting treatments in any of these measurements, though abundances of arthropods in the sap-feeding trophic guilds were appreciably greater (although not significantly) on netted compared to un-netted shrubs. Our results suggest that in the short-term, either top-down effects in this sage-steppe ecosystem are minimal, and/or inter-trophic interactions (vertebrate predators-arthropods-plants) are relatively weak and more dependent on bottom-up processes that are linked with abiotic variables.


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