Introduced plant species may affect local plant and animal community diversity and species richness. We studied the association between varying densities of two introduced wetland plants, purple loosestrife (Lythrum salicaria) and reed canary grass (Phalaris arundinacea), on plant and moth species richness at sites within 24 palustrine emergent wetlands in Oregon, Washington, and Idaho. Seven wetlands were dominated by canary grass, seven were dominated by loosestrife, and ten were reference wetlands dominated by neither canary grass nor loosestrife. We measured plant community composition as percent cover and sampled the moth community using blacklight traps. One hundred and sixty-nine plant and 178 moth species were identified. As the mean percent cover of canary grass and purple loosestrife increased from 0 to 91%, plant species richness declined from 45 to 4. We found a strong positive correlation between moth and plant species richness in rural wetlands. However, urban wetlands did not show this relationship. A strong negative association between reed canary grass and purple loosestrife abundance and plant and moth species diversity suggests that these two invasive species reduce local biodiversity. In addition, our data suggest that the influence of urban landscapes reduces moth species richness and abundance.
Keywords: urban wetlands, lepidoptera
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