Title

A tangled web: The effects of an invasive plant on the Montana native Dictyna spider, their prey items, and the parasitoid wasp that feeds on them

Presenter Information

Mary Bruen

Presentation Type

Poster

Abstract

A continuing challenge in assessing the role of invasive species is determining their long-term effect on an ecosystem. In this study, I look at the effect of an invasive plant on insect community assemblage to better understand consequences of non-native species on biodiversity. Recent increases in the abundance of the Montana-native Dictyna spider can be attributed to the invasion of Spotted Knapweed, Centurea maculosa. The rigid stalk and woody stems of knapweed plants offer Dictyna spiders an ideal substrate for web building. Although the effect of knapweed on Dictyna spider populations has been well investigated, no studies to date have examined the effect on the diversity and abundance of Dictyna prey species—insects. During the summer of 2011, I sampled the relative diversity and abundance of Dictyna prey in three paired sites in western Montana. I explored how prey species varied in knapweed-invaded and native regions. This project may help managers gain insight into how insect community assemblage has changed, or not changed, in response to knapweed invasion and Dictyna proliferation. This study also examines the abundance of a parasitoid wasp, Catolaccus (family Pteromalidae), in the insect community assemblage. This wasp has been known to parasitize Dictyna spider egg sacs, reducing the number of Dictyna spiderlings dramatically. In evaluating the number of parasitoid wasps in both invaded and native grasslands, the effect of parasitism on Dictyna proliferation and knapweed invasion may be better understood. This project provides insight into a unique type of trophic cascade where knapweed, a primary producer, causes significant alterations in higher-level trophic organisms.

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A tangled web: The effects of an invasive plant on the Montana native Dictyna spider, their prey items, and the parasitoid wasp that feeds on them

UC Ballroom

A continuing challenge in assessing the role of invasive species is determining their long-term effect on an ecosystem. In this study, I look at the effect of an invasive plant on insect community assemblage to better understand consequences of non-native species on biodiversity. Recent increases in the abundance of the Montana-native Dictyna spider can be attributed to the invasion of Spotted Knapweed, Centurea maculosa. The rigid stalk and woody stems of knapweed plants offer Dictyna spiders an ideal substrate for web building. Although the effect of knapweed on Dictyna spider populations has been well investigated, no studies to date have examined the effect on the diversity and abundance of Dictyna prey species—insects. During the summer of 2011, I sampled the relative diversity and abundance of Dictyna prey in three paired sites in western Montana. I explored how prey species varied in knapweed-invaded and native regions. This project may help managers gain insight into how insect community assemblage has changed, or not changed, in response to knapweed invasion and Dictyna proliferation. This study also examines the abundance of a parasitoid wasp, Catolaccus (family Pteromalidae), in the insect community assemblage. This wasp has been known to parasitize Dictyna spider egg sacs, reducing the number of Dictyna spiderlings dramatically. In evaluating the number of parasitoid wasps in both invaded and native grasslands, the effect of parasitism on Dictyna proliferation and knapweed invasion may be better understood. This project provides insight into a unique type of trophic cascade where knapweed, a primary producer, causes significant alterations in higher-level trophic organisms.