Dryad

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Published August 9, 2022 | Version v1
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Sampling bias exaggerates a textbook example of a trophic cascade

Creators

  • 1. Utah State University
  • 2. University of Wisconsin–Stevens Point

Description

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 nonrandom 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)] behavior 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 3-8 compared to random sampling because it favored 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 nonrandom sampling described. Our findings highlight the critical importance of basic sampling principles (e.g., randomization) for achieving an accurate understanding of trophic cascades in terrestrial wildlife systems.

Notes

This dataset has 18,792 records, including 18,623 records of individual young aspen (plants > 1 year-old & < 600 cm) and 169 records of plots with no young aspen ("zero plots"). Records of individual young aspen (N = 18,623) were used in the majority of analyses (Fig. 2-5a,b), including generalized linear mixed models (GLMMs) that tested how the effect of year on browsing, height, and recruitment of stems differed by sampling method. This dataset was also used to model the effect of stem height on browsing to estimate the preferred browse height (PBH) and browse escape height (BEH). The full dataset that includes plots with no young aspen was only used to calculate the percentage of plots and stands each year with median heights greater than 200 (Fig. 5c) or 300 cm (Fig. 5d).  

The dataframe has the following 6 columns:  

  1.  Plot: individual identifier for each of 113 plots distributed randomly across the study area. Each plot was a 1 × 20 m belt transect located randomly within an aspen stand 
  2. Year: year in which aspen was sampled
  3. Tree: individual identifier for each stem within a plot
  4. Browse: denotes the browsing status (browsed = 1,unbrowsed = 0) of the leader (tallest) stem. A leader was 'browsed' if its growth from the previous growing season had been eaten
  5. Height: height (cm) of the leader stem of each individual aspen
  6. Type: sampling method. Every young aspen within a plot is a "random" stem, and each of the five tallest young aspen within the stand is a "5T" stem.

Funding provided by: U.S. National Science Foundation
Crossref Funder Registry ID: http://dx.doi.org/10.13039/100000001
Award Number: DGE-1633756

Funding provided by: University of Wyoming-National Park Service Small Grant Program*
Crossref Funder Registry ID:
Award Number: 1003867-USU

Funding provided by: Yellowstone National Park*
Crossref Funder Registry ID:
Award Number:

Funding provided by: Utah State University
Crossref Funder Registry ID: http://dx.doi.org/10.13039/100006630
Award Number:

Funding provided by: S.J. and Jessie E. Quinney Doctoral Fellowship*
Crossref Funder Registry ID:
Award Number:

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Additional details

Related works

Is cited by
10.1101/2020.05.05.079459 (DOI)
10.1111/ele.13915 (DOI)
Is source of
10.5061/dryad.2z34tmpnj (DOI)