Abstract Detail

Reproductive biology

Russell, Francis Leland [1], Houseman, Gregory R. [2].

Effects of herbivory and soil fertility on tall thistle (Cirsium altissimum) population density and growth.

Soil fertility is often hypothesized to influence the amount of herbivore damage that plants suffer and plants’ abilities to compensate for damage. While interactive effects of soil resources and herbivory on individual plant performance have been extensively investigated, few studies have examined whether herbivores’ effects on plant populations depend on soil resource availability. In a restored prairie, since 2010 we have employed a factorial experiment involving manipulation of herbivore access and soil fertility to examine such interactive effects. First, we are addressing whether herbivory by insects, aboveground mammals and digging mammals individually and in combination affects tall thistle (Cirsium altissimum) reproduction, density and population growth. Second, we ask whether these herbivores’ effects on tall thistle populations vary between ambient and enhanced soil fertility. Mining of tall thistle branch meristems by insects was more common on plants with augmented soil resources in two years and more common on plants with ambient resources in one year. Other forms of herbivore damage were unaffected by soil fertility. We found no evidence that herbivores’ effects upon tall thistle seed production, population density or growth rate depended upon soil resources. Nevertheless, individual treatments had strong effects. Tall thistle densities were lower in fertilized than control plots in three of five years. Aboveground vertebrate herbivores were associated with higher thistle densities in the second and fifth years of the study. Insect herbivores were associated with higher thistle densities in the second year of the study, but suppressed tall thistle densities in the third, fourth and fifth years. Suppressive effects of insect herbivores on tall thistle densities resulted from insects reducing thistle population growth rate in a single year (the third year of the study), but densities in plots with ambient vs. reduced insect herbivory had not converged three years later. Although insect herbivores reduced population growth in only one year, they suppressed tall thistle seed production in three of four years for which we have seed counts. Microsite limitation of thistle recruitment may be common at the study site due to accumulated plant litter. After five years of experimental manipulation, our results indicate that tall thistle populations are often affected by soil resources and herbivores, but these population limiting factors operate independently.

1 - Wichita State University, Department Of Biological Sciences, 1845 Fairmount, Wichita, KS, 67260, USA
2 - Wichita State University, Department of Biological Sciences, 1845 Fairmount, Wichita, KS, 67260, United States

Keywords:
Cirsium
herbivory
population growth
soil resources.

Presentation Type: Oral Paper:Papers for Topics
Session: 2
Location: Salon 1/The Shaw Conference Centre
Date: Monday, July 27th, 2015
Time: 10:45 AM
Number: 2010
Abstract ID:370
Candidate for Awards:None