Sampling bias exaggerates a textbook example of a trophic cascade.

• Published in: Ecology Letters
• Main Authors: Brice, Elaine M, Larsen, Eric J, MacNulty, Daniel R
• Format: Manuscript
• Language: English
• Published: Wiley 2022
• Subjects: aspen; carnivore; elk; non-random sampling; predator indirect effects; preferred browsing height; sampling bias; trophic cascade; ungulate; wolf; Canis lupus
• Online Access: https://doi.org/10.1111/ele.13915; https://pubmed.ncbi.nlm.nih.gov/34748261; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9298920/

Understanding trophic cascades in terrestrial wildlife communities is a major challenge because these systems are difficult to sample properly. We show how a tradition of non-random sampling has confounded this understanding in a textbook system (Yellowstone National Park) where carnivore [Canis lupus (wolf)] recovery is associated with a trophic cascade involving changes in herbivore [Cervus canadensis (elk)] behaviour and density that promote plant regeneration. Long-term data indicate a practice of sampling only the tallest young plants overestimated regeneration of overstory aspen (Populus tremuloides) by a factor of 4-7 compared to random sampling because it favoured plants taller than the preferred browsing height of elk and overlooked non-regenerating aspen stands. Random sampling described a trophic cascade, but it was weaker than the one that non-random sampling described. Our findings highlight the critical importance of basic sampling principles (e.g. randomisation) for achieving an accurate understanding of trophic cascades in terrestrial wildlife systems.