Steven, Janet , Prendeville, Holly , Galloway, Laura .
Variation in the intensity of deer herbivory and its impact on fecundity across a latitudinal gradient in Campanulastrum americanum, a monocarpic herb.
In many plant populations, browsing by white-tailed deer reduces plant abundance and fecundity. Across its range, a palatable plant species may escape the impacts of herbivory in some locations if deer browse is intense in only a few populations, if some populations show greater resistance to or tolerance of herbivory, or if variation in plant size and life history offsets the impact of browse. We examined the extent to which deer browsing and subsequent reductions in fecundity are pervasive across a latitudinal gradient in the palatable plant species Campanulastrum americanum, a monocarpic annual or biennial herb. In 17 populations from Michigan to Florida, we measured the frequency of deer herbivory and its effect on fruit and seed set. The percent of bolting plants browsed within a population ranged from 9% to 95%, and was greater in southern populations. Larger plants and plants in sunnier locations within populations were more likely to be eaten. On average, herbivory reduced fruit set and seed set. Although browse was greater in the south, plants in the south also tended to be larger, as measured by stem diameter, and contain more seeds per fruit; as a result, the reduction in fruit and seed set due to herbivory was similar across all sites. In one population in Indiana, the linear increase in fruit number as stem diameter increased was greater for browsed plants, suggesting that plants are actually increasing seed production after browse. However, this was the only population in which we found evidence of tolerance to herbivory through increased growth. We also estimated population growth rates using measures of plant survival and seed production in each population. Growth rates ranged from 0.18 to 4.3, and there was no relationship between growth rate and the percent of bolting plants that were eaten by deer. These findings suggest that while deer browse is significant in some populations and negatively affects fecundity in most populations, variation in browsing intensity and plant size traits along the same gradient mitigates the effect of browsing.
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1 - Sweet Briar College, Department Of Biology, Guion Science Center, Sweet Briar, VA, 24595, USA
2 - University Of Virginia, Department Of Biology, P.O. Box 400328, Charlottesville, VA, 22904-4328, USA
3 - University Of Virginia, P.O. Box 400328, CHARLOTTESVILLE, VA, 22904-4328, USA
population growth rates
Presentation Type: Oral Paper:Papers for Sections
Location: Franklin B/Hyatt
Date: Wednesday, July 11th, 2012
Time: 11:00 AM