COS 230-1 - The effects of advanced plant phenology on herbivory and plant demography.

Abstract: The annual timing of life-cycle events, known as phenology, can have strong effects on survival, growth, and reproduction, and can also affect species interactions. Phenology is often regulated by seasonal climatic cues, and climate change is advancing phenology to earlier dates in many species across the world. However, plant phenology is advancing at a faster rate than the organisms that eat plants (herbivores), which invites the possibility of temporal misalignment between plants and herbivores that typically interact. Herbivory strongly impacts plant survival, growth, and reproduction, and therefore plant populations. Changes to plant populations can have ecosystem-wide consequences, so it is critical to investigate how altered timing of plant-herbivore interactions affects plants. However, almost no research considering this link focuses on consequences for plants, instead focusing on the herbivores. Our research therefore investigates how advanced plant phenology changes herbivory and subsequently plant growth and reproduction of four subalpine plant species at the Rocky Mountain Biological Laboratory in Gothic, Colorado in 2022. Our main questions were: Q1) How does earlier plant phenology alter the amount of herbivory experienced by plants? Q2) Do altered amounts of herbivory between early and control plots affect plant vital rates, including vegetative growth or reproduction? To address these questions, we used shade cloths to advance spring snowmelt date, which in turn induces earlier plant phenology. To decipher how plant performance is affected by altered plant-herbivore phenology, we observed the phenology, herbivory, and plant growth and reproduction of four species: Delphinium nuttallianum, Geum triflorum, Linum lewisii, and Delphinium barbeyi. Snowmelt was earlier in the treatment plots compared to controls (2 ± 0.18 days, mean ± se), and plants of most species were taller (D. nuttallianum flower stalk height: p = 0.05864; G. triflorum length of longest leaf: p = 0.07413; D. barbeyi tallest stalk height: p </em>= 0.09701) early in the season in the early plots compared to controls, suggesting that plants in the early snowmelt treatment started to grow earlier. However, herbivory was not different between treatments for any species (proportion of damaged leaves or stalks for all species: p > 0.2). These results suggest that plant phenology, at least to the extent observed here, does not seem to alter herbivory or plant performance.