Temperature-dependent herbivore nutritional traits affect population dynamics and persistence

Abstract

Herbivores can vary in their relative requirements for nutrients and carbon, with important consequences for consumer-resource dynamics and nutrient cycling. The nutrient (phosphorus) and carbon requirements of herbivore growth have both been found to increase at temperature extremes, yet the consequences of these thermal responses for herbivore-autotroph population dynamics have not been explored. Here, we develop and analyze a stoichiometrically-explicit, temperature-dependent model of herbivore-autotroph systems to evaluate how these two thermal responses of herbivore nutritional traits affect population responses to temperature and phosphorus supply. We find contrasting effects of increased phosphorus or carbon demands at temperature extremes. Increases in herbivore phosphorus demands relatively strongly restricts the range of temperatures at which the herbivore population persists and slightly decreases the stability of population dynamics at high phosphorus supplies. In contrast, increases in the carbon requirements of herbivore growth slightly decreases the temperature range supporting herbivore persistence and stabilizes the system under phosphorus enrichment. These contrasting effects of herbivore nutrient and carbon demands reflect differences in the ecological contexts at which they influence herbivore performance. Increased nutrient requirements impair herbivore productivity near the herbivore persistence boundary where autotrophs are abundant and nutrient-poor, whereas high carbon demands decrease herbivore productivity near the stability boundary where autotrophs are at low density and nutrient-rich. The thermal response of herbivore nutritional traits may therefore be an important factor influencing population responses to warming and nutrient enrichment.