首页|Chronic, low-level nitrogen deposition enhances abundances of ant-protected herbivores inhabiting an imperiled foundation species
Chronic, low-level nitrogen deposition enhances abundances of ant-protected herbivores inhabiting an imperiled foundation species
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NSTL
Elsevier
Atmospheric nitrogen (N) deposition is driving changes in plant assemblages worldwide, but animal responses are not well understood, especially in relation to current widespread rates of low-level N deposition. Big sagebrush (Artemisia tridentata) is a foundation species in steppe ecosystems of western North America, where elevated, but low-level N deposition is prevalent. Sagebrush hosts numerous herbivorous and predatory arthropods, some of which form mutualistic (i.e. mutually beneficial) herbivore-predator associations that may be harmful for sagebrush. Here, I evaluated the response of a sagebrush arthropod assemblage to four and nine years of low-level N enrichment in Colorado, USA. Though sagebrush cover and arthropod abundances were not different in the fourth year, by the ninth year, N additions increased arthropod abundances due to greater numbers of sap-feeding insects that are mutualist partners of predaceous ants. Ant and non-mutualist herbivore abundances did not significantly respond to N treatments in the ninth year, but non-mutualist predators were only found in ambient N plots, suggesting ants provided greater anti-predator protection for mutualist herbivores under N enrichment. These responses occurred during drought conditions, which may have increased sagebrush nutritional quality for sap-feeding insects. Sagebrush is experiencing multiple stressors that are transforming steppe ecosystems; these results suggest chronic exposure to common rates of low-level N deposition may create further stress as herbivorous insects proliferate. Additional work is needed to understand and manage the repercussions of N deposition for plant-animal assemblages, particularly in contexts including species of conservation concern and both mutualistic and antagonistic species interactions.
NSTL
Elsevier
