Spider diversity response to garlic mustard (Alliaria petiolata) invasion in a Wisconsin forest understory

Author / Creator

Sprovach, Megan C., author

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Summary

The invasive herb garlic mustard is considered a major contributor to biodiversity loss in forest understories throughout the United States, including in northeastern Wisconsin. Research on the eff...

The invasive herb garlic mustard is considered a major contributor to biodiversity loss in forest understories throughout the United States, including in northeastern Wisconsin. Research on the effect of garlic mustard invasion on spiders is limited. The purpose of this project is examine the effect of garlic mustard invasion on the spider community structure at Bay Beach Wildlife Sanctuary in Green Bay, Wisconsin. Four pitfall traps per each of thirty 5 X 5-meter plots, representing a gradient of garlic mustard cover, were sampled monthly from June to September in 2015. Time-controlled vegetative sampling was conducted in each plot at the beginning and end of the collection season and all vegetation within each plot was identified to species. Spider species richness, spider Shannon diversity, and the ratio of web-building to wandering spider species were quantified at the plot level. The spider richness, diversity and guild ratios were modeled against garlic mustard cover. Individual spider species were examined for correlation with garlic mustard cover. When accounting for plant height deviation, the relationship between Shannon diversity and garlic mustard cover is inconclusive, but spider species richness increased with greater garlic mustard cover. The ratio of web-building to wandering spiders was not correlated with garlic mustard cover. June vegetative samples of the native linyphiid Ceraticelus fissiceps were also positively correlated with garlic mustard, but not strongly enough to be used as an indicator for plot-level ecological change. The opportunistic native linyphiid Diplostyla concolor and the native salticid Pelegrina proterva were also commonly found in the plots. These results suggest that the presence of an invasive species in a habitat could benefit spider populations under unusually low biodiversity conditions, but caution must be exercised when considering these results for policy implications.

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