URI_Research_Magazine_Momentum_Spring_2016_Melissa-McCarthy

Evan Preisser Associate Professor Biological Sciences

Preisser pictured with his students

Leading the charge to save the forests from an invasive species that threatens the ecosystem at its very foundation.

often provide a benefit to plant material by consuming herbivores that would otherwise eat the plants.” In terms of indirect influences, a major factor is what is known as a non-consumptive effect between predator and prey. “Prey are much more motivated to avoid being eaten than predators are to eat them,” Preisser explains. “It’s what’s called the life-dinner principle. If a predator and prey interact and the predator loses, it loses its dinner. If the prey loses, it loses its life.” Preisser’s work with food webs led him to become concerned about an invasive species known as the hemlock woolly adelgid and its devastating effects on eastern hemlock trees. The loss of these trees, which can be found primarily in the Northeast, could damage the region’s ecosystem at its bedrock. “Eastern hemlock is a foundational species — an organism that creates or maintains a unique habitat,” says Preisser. “Eastern hemlock is the only native shade- tolerant conifer on the East Coast. Because of that, it plays

an incredibly important role in creating habitats for a series of organisms that like cooler or moister microclimates and for shading headwater streams — in areas where trout breed.” If you lose eastern hemlock, you would have other trees replace it, but those would not be trees that would be capable of keeping the water cool enough for trout and other cool water invertebrates. Hence, adelgids are an enormous problem. Arriving from Japan circa 1950, adelgids settled on one northeastern species alone, the eastern hemlock trees. The tiny pests, which suck out the tree’s fluids, have very few natural predators, allowing their populations to boom. And if the adelgids attacking trees is not enough to kill them, these insects weaken the hemlocks to a point where another invasive species from Asia, the elongate hemlock scale, can come in and finish the job. Naturally, this has led to a scramble to mitigate the damage wrought by these insects. Traditionally, according to Preisser, the U.S. Forest Service has taken a lead

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