When your herbivore is your fertilizer: the impact of periodical cicadas on tree growth
Contributed by Ash Zemenick @mtn_ash & Louie Yang @chasingcicadas
Animals, Community ecology, Competition, Consumption, Ecology, Experimental, Field, Fundamental research, Interactions, Natural history, North America, Plants, Terrestrial
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Louie H. Yang and Richard Karban. 2019. The effects of pulsed fertilization and chronic herbivory by periodical cicadas on tree growth. Ecology 100(6): e02705 link
Slide 1: Researcher’s Background
Louie Yang is a professor in the Department of Entomology and Nematology at the University of California, Davis. He is a community ecologist who studies how species interactions change over time, usually focusing on plant-insect interactions. Louie is also an accomplished and active mentor and teacher to students and the public. He is a cofounder of the Research Scholars Program in Insect Biology at UC Davis and the founder of the Monitoring Milkweed-Monarch Interactions for Learning and Conservation (MMMILC) Project.
PB: Why did you become a biologist?
LY: I’ve always liked animals and wildness.
PB: What is your favorite part about your job?
LY: Discovery, new ideas, passing along good advice, intellectual freedom
PB: What advice do you have for aspiring biologists?
LY: Never give up.
Slide 2: Research Overview
Take home message of study
Louie Yang and Rick Karban studied the impact of periodical cicadas (Magicicada spp.) on American sycamore trees (Plantanus occidentalis). They found that cicada fertilization strongly increased tree growth in the year of emergence, creating differences in tree size that persisted at least 2 yr later. Even though cicadas are root feeders, they did not find any reductions in tree growth associated with cicada herbivory in any year of this experiment. However, cicada herbivory reduced the densities of, and damage from, other aboveground herbivores.
Periodical cicada adults represent a pulsed detrital subsidy that fertilizes plants, and live cicada nymphs are long-lived root-feeding herbivores. Figure 1 from Yang and Karban 2019 shows the study species and study area. The caption reads: “ (a) Dead cicada carcasses can represent a significant pulsed detrital subsidy. (b) Cicadas oviposit into egg-nest incision in woody branches. (c) Experimental trees in May 2015. (d) The same trees in July 2017.”
Slide 3: Key Research Points
Top panel: Tree growth (y-axis) over time (x-axis). Trees grew taller when they were fertilized by cicadas (blue lines) compared to when they were not (red lines). From Figure 2 in Yang and Karban 2019.
Bottom panel: The number of bagworms per tree (y-axis) was lower on trees that experienced root herbivory by cicadas (x-axis). From Figure 3 in Yang and Karban 2019.
Even though species interactions are multifaceted, they are often reduced to one dimension (e.g. cicadas are considered herbivores and bad for trees even though they are also important fertilizers). Research that tries to disentangle the various impacts one species may have on another are an important step forward in our understanding of the natural world.