Abstract Detail



Ecology

Ivey, Christopher [1], Wright, Jessica [2], MacDonald, Brandon [3], Sork, Victoria [4].

Negative relationships between galling insect abundance and relative growth rates in a large provenance test of valley oak (Quercus lobata) fail to support the Plant Vigor Hypothesis.

Because of their ability to convert carbon dioxide into carbohydrates, plants endure an unyielding siege from diverse natural enemies. The “Plant Vigor Hypothesis” proposes that robust or vigorously growing individuals are preferred hosts of herbivorous insects and therefore more likely to experience attack. We tested this hypothesis in a recently established provenance trial of the iconic keystone species of California’s central valley, Quercus lobata, involving 672 maternal families collected throughout its range and fully replicated in two field sites. On each of over 6,500 trees the abundance of leaf- and stem-galls induced by insects was scored as a measure of vulnerability to herbivore attack. In each of two years, tree height was measured at the end of the growing season, from which relative growth rate was calculated as a measure of plant vigor. We predicted that a positive relationship between gall abundance and relative growth rate would indicate support for the Plant Vigor Hypothesis. Instead, at both sites, we found negative relationships between abundance of the most common gall species and relative growth rate. In addition, we found a negative relationship between gall species richness and relative growth rate at the site where diversity of galls was highest. These results fail to support the Plant Vigor Hypothesis, and may indicate a negative effect of galling insects on oak growth rates or an inability of plants with high growth rates to defend against galling insects.  We will discuss the extent to which gall abundance can be explained by tree maternal genotype as well as the climate and geography of the maternal seed source.


1 - California State University, Chico, Biological Sciences, 400 W 1st St., Chico, CA, 95929, United States
2 - U.S.D.A. Forest Service, Pacific Southwest Research Station, 1731 Research Park Dr., Davis, CA, 95618, USA
3 - University of California, Los Angeles, Department of Ecology and Evolutionary Biology, 610 Charles E. Young Drive East, Los Angeles, CA, 90095, USA
4 - UCLA, ECOL & EVOL BIOL, Box 957239 , Los Angeles, CA, 90095, United States

Keywords:
Quercus
herbivory
galls
relative growth rate
common garden
plant vigor hypothesis
Plant-Insect interaction
plant defense.

Presentation Type: Poster
Number: PEC014
Abstract ID:316
Candidate for Awards:None


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