Biologist, students study invasive species

Skidmore College biologist Joshua Ness spent much of the summer tracking a suspected "invasional meltdown." Fortunately, his work did not involve donning a hazardous material suit and face mask, or contact with toxic materials. Instead, his toolkit included a kayak, a bag of Chips Ahoy cookies, and a storehouse of patience.

	Assistant Professor of Biology Josh Ness

Ness, an assistant professor of biology, along with Skidmore students Erin Kenison, Peter Leipzig-Scott (both Class of '09) and Doug Morin (Class of '07), visited the Kayaderoserras, Hoosic, and Battenkill watersheds to study the invasion of Japanese knotweed and its relationship with the European fire ant, Myrmica rubra. The research was supported by Skidmore's Water Resource Institute and a grant Ness and Dr. Manuel Morales (Department of Biology, Williams College) received from the New York State Biodiversity Research Institute.

Both the plant and ant species arrived in the U.S. in the late 1800s and now thrive in riverside habitats. Japanese knotweed replaces native riparian plant species, alters stream water flow and stream bank stability, and decreases wildlife habitat. The European fire ant is the only ant in the Northeast with a painful sting (comparable to a wasp) and is considered a nuisance pest to humans. Earlier research has shown that native ant diversity and abundance decreased after M. rubra invaded coastal sites in Maine, and a similar process seems to be occurring in the Hoosic River watershed.

An "invasional meltdown" happens when a pair of invasive species synergistically interacts. The results of this relationship are potentially more serious than the effects that either species would have on its own, according to Ness. The Japanese knotweed produces carbohydrate-rich nectar that nourishes the ants. Ness and his student collaborators theorized that the ants were protecting the plants from herbivores; this summer they tested the hypothesis that these non-native ant and plant species were engaged in a mutually beneficial relationship, one with the potential to reduce the number of native ant species and eliminate native plant species in the region's watersheds.

The research team mapped locations of knotweed and ants in areas along the Hoosic, Battenkill, and Kayaderosseras, all of which are part of the upper Hudson River watershed. Such mapping is critical because it provides a point of reference and "helps us to describe particular sites or habitats that are vulnerable to the two invasions," explained Ness. Under good conditions, the knotweed can grow up to four centimeters a day, flourishing in the wetland areas and sending new propagules downstream. It crowds out native plants and supports few insects or vertebrates, creating "a biological dead zone," Ness said.

Student researcher Kenison took the lead on mapping knotweed in the Battenkill and Kayderosseras regions. Her map can facilitate eradication programs and provide a pre-invasion description of the native communities in sites where the species have not currently located. In addition, she monitored knotweed leaves in the stream to learn more about what in-stream invertebrates might be feeding on the leaves. Because leaves from streamside plants provide much of the energy for food webs in the stream, how insects respond to knotweed versus other leaves may indirectly influence fish in the streams.

To learn more about the distribution and behavior of native ants and M. rubra, student researcher Morin used baits?in the form of Chips Ahoy cookies?to draw the ants. Ness explained that because the cookies have a high concentration of carbohydrates and fat, they are very appealing to ants. The researchers wanted to learn about the interaction between ants and knotweed, and whether particular ants were more or less common in areas with knotweed. The baits also helped the team identify areas not yet invaded by M. rubra.

Student researcher Leipzig-Scott intentionally damaged knotweed leaves to test the hypothesis that ants would rush to defend the plant. The trio cut the leaves of the plants to mimic the type of damage that the plant might naturally endure, and waited for the ants to react. Often three or four times the usual number of ants would respond to the damage to "protect" the plant.

Ness reported that with one exception, the Japanese knotweed seems to have no important natural enemies in this region. "Most of its natural enemies may still be in Japan," he said. However, the researchers did find patches of knotweed under attack by Japanese beetles, prompting Ness to comment, "This is the first time I've seen the Japanese beetle do something useful." It is possible, he added, that the beetle could help keep the knotweed in check.

The next step in the study is to observe the relationship between the ants and the beetles, and contrast the responses of the native ants and M. rubra. One hypothetical scenario, in which the Japanese beetles are deterred by the stings of the European fire ant but ignore the native ants, may be a recipe for 'invasional meltdown.' If that is the case, "Do we deal with the knotweed first, or the ants?" asks Ness. The research will continue during the upcoming academic year, with data analysis next on the agenda.

He acknowledged that he hopes an invasional meltdown is not occurring. "But either way, we'll have a better sense of what situations may favor those meltdowns versus keeping them in check."