The primacy of density-mediated indirect effects in a community of wolves, elk, and aspen

The removal or addition of a predator in an ecosystem can trigger a trophic cascade, whereby the predator indirectly influences plants and/or abiotic processes via direct effects on its herbivore prey. A trophic cascade can operate through a density-mediated indirect effect (DMIE), where the predator reduces herbivore density via predation, and/or through a trait-mediated indirect effect (TMIE), where the predator induces an herbivore trait response that modifies the herbivore’s effect on plants. Manipulative experiments suggest that TMIEs are an equivalent or more important driver of trophic cascades than are DMIEs. Whether this applies generally in nature is uncertain because few studies have directly compared the magnitudes of trait- and density-mediated indirect effects on natural unmanipulated field patterns. A TMIE is often invoked to explain the textbook trophic cascade involving wolves (Canis lupus), elk (Cervus canadensis), and aspen (Populus tremuloides) in northern Yellowston..., Aspen data
 
Beginning in 1999, we measured young aspen height and browsing at 113 stands selected in a stratified random sample reflecting high and low wolf use areas (see Brice, Larsen, and MacNulty 2022 for details). All stands were selected from aerial photographs taken after the 1988 fires; as such, selected aspen stands were those whose overstory at least partially survived the 1988 fires. Each stand contained a 20-x-1 m belt transect, and we surveyed all young aspen (≤ 600 cm tall, “stems”) within the transect (“plot”) at the end of the growing season (late July – September) each year. For each stem, we measured height of the leader (i.e., tallest stem), and whether the leader was browsed the previous winter. The number of stands sampled each year varied from 61 – 113 (μ = 97.3, σ = 18.3), and the number of plots with stems each year varied from 55 – 108 (μ = 84.9, σ = 17.2). Sampling occurred annually from 1999-2019, excluding 2000 and 2015, resulting in 26,012 stem-level observ..., , # Data from: The primacy of density-mediated indirect effects in a community of wolves, elk, and aspen

[https://doi.org/10.5061/dryad.2bvq83c0d](https://doi.org/10.5061/dryad.2bvq83c0d)

The file \"BriceEtAl2024_Data.xlsx\" includes all data needed to replicate models of aspen browse and recruitment probability as part of a test on density- and trait-mediated trophic cascades in Yellowstone National Park. The file \"BriceEtAl2024_SupportingTables.xlsx\" contains six supplemental tables from our analysis.

## File Structure

### BriceEtAl2024\_Data.xlsx

This file has data on 26,012 individual young aspen collected between 1999-2019. Data were not collected in 2000 or 2015. The file has 3 tabs: one for data on aspen browse, and two for data on aspen recruitment. For the browsing data, each row represents an individual aspen at a specific site (i.e., \"Plot\", Column A), and the columns have data on whether that individual aspen was browsed by elk, and what it's height was. There are 10 column...