Responses |
Corresponding author: William Wetzel ( wcwetzel@msu.edu ) Academic editor: Michael Rostás
© 2019 William Wetzel, Heather Kharouba, Moria Robinson, Marcel Holyoak, Richard Karban.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Wetzel W, Kharouba H, Robinson M, Holyoak M, Karban R (2019) Plant trait covariance and nonlinear averaging: a reply to Koussoroplis et al. Rethinking Ecology 4: 115-118. https://doi.org/10.3897/rethinkingecology.4.32767
|
Nonlinear averaging, Jensen’s inequality, intraspecific trait variability, plant diversity, plant–herbivore interactions, consumer–resource dynamics
In a previous paper, we re-analyzed data from 76 published studies on the relationships between plant trait levels and insect herbivore performance and found that variation in plant nutrients reduces insect herbivore performance via nonlinear averaging (
Their first point is that reporting a mean effect size masked important negative and positive effects because opposite signs with similar magnitudes would average to zero.
Frequency distribution of plant defense effect sizes. The vertical red line indicates the mean effect size calculated using a random effects meta-analysis model.
The second point is that we considered defenses individually and ignored interactions between traits. This was necessary because of the scarcity of published experimental data on interactions. Of the 76 studies that met our search criteria, only nine examined interactions, and only one of those tested enough levels to quantify the multivariate nonlinearities that result from interactions. We fully agree that interactions have potential to make defense variance important. However, current data make it premature to conclude that we have underestimated the effects of defense variance on herbivores by ignoring trait interactions. As
In addition to trait interactions, there are also several other mechanisms that could lead defense variance to influence herbivores in ways we were unable to evaluate due to a lack of data. Variation in defense traits could prevent herbivores from physiologically acclimating to host plants (
We join
We thank M. Meek, G. Bradburd, M. Weber, and C. Edwards for helpful discussion.