Date of Award

January 2019

Degree Type

Open Access Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

First Advisor

Cy L. Mott

Second Advisor

Amy Braccia

Third Advisor

Jennifer M. Koslow

Abstract

Lonicera maackii (Amur Honeysuckle) is an invasive woody plant species that is present across the United States. Previous studies have assessed the biotic effects of honeysuckle, as well as abiotic effects such as changes in soil chemistry, ground level light, and forest floor temperature. Although directs effects of L. maackii on native terrestrial plant communities are well studied, little is known about its indirect effects, especially in aquatic ecosystems. Based on limited prior studies, I predicted addition of L. maackii leaves to aquatic systems would increase mortality of a top amphibian predator due to the release of phenolic compounds that inhibit respiration. A mesocosm experiment was developed to characterize the cascading effects of increased top predator (Ambystoma maculatum) mortality on larval salamander growth, macroinvertebrate densities, zooplankton densities, leaf litter mass loss, chlorophyll a abundance, biofilm growth, and availability of soluble nutrients. Of the 20 mesocosms that contained larval A. maculatum, only 11 produced metamorphs, and only one mesocosm with leaf litter from L. maackii produced metamorphs. All 10 mesocosms containing A. maculatum larvae and native leaf litter produced metamorphs. A total of 117 metamorphs were retrieved from all mesocosms, and only three of those 117 were retrieved from mesocosms with leaf litter from L. maackii. Salamander survival and growth rates (mm/day) were significantly lower in mesocosms with L. maackii than in mesocosms with native leaf litter alone. Mesocosms with L. maackii leaf litter also contained substantially more mosquito larvae, suggesting reduced water quality. There was no indication that apex predator mortality in L. maackii mesocosms altered aquatic ecosystem functions. However, increased mass loss occurred in leaf packs containing L. maackii compared to leaf packs containing native leaf litter removed from the same mesocosm, which was not caused by greater invertebrate densities within L. maackii packs. I also found there to be an oily sheen on the water surface of mesocosms containing L. maackii leaf litter, which could hinder gill-breathing by amphibians. Relatively high invertebrate densities and diversity may have served as a buffer for lower trophic levels, such that they were not affected when A. maculatum individuals were eliminated from mesocosms due to exposure to L. maackii phenolic compounds. The results of this study will help complete the overall picture of the possible consequences of biological invasion.

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