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Part three of biotic change in hemlock forests - Ants and spiders

Wednesday, August 1, 2012, by Yvan Delgado de la Flor
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Eastern hemlock is a foundation species in eastern North America and plays a critical role in the local biota. This tree deeply shades the soil, creating a unique microclimate for some species. Currently, hemlocks are dying rapidly due to the invasive woolly adelgid, a nonnative phloem-feeding insect, causing alterations to the understory microclimates. Hemlocks are being replaced slowly by hardwood forests. All of these changes affect the entire ecosystem and result in the local extinction of some arthropods; for example, some ants and spiders are very sensitive to changes in temperatures. In my study this summer I measured the impact of hemlock loss on ant and spider communities in hemlock stands and contrasted their assemblages in hemlock and hardwood stands. 

 I.hypothesized that the loss of eastern hemlock and associated increase in forest-floor temperature would result in the extirpation of some ant and spider genera. The effect of the adelgid was mimicked with four canopy-manipulation treatments: hemlock (control), girdled hemlock, logged hemlock, and hardwood (control). Pitfall traps were sampled throughout the summer in all treatments; ants and spiders collected were identified to genus. Initial results suggest little differences among the treatments, but sample size remains small because most of the pitfall traps will not be collected until late July. Eastern hemlocks occupy large area of late successional forests in eastern North America and the effect and impact will be better observed in 20+ years, when hemlocks will be locally extinct, potentially leading to the extirpation of local species, and the alteration of food webs and ecosystems. 

This summer I work with Aaron Ellison, Relena Ribbons and Clarisse Hart. My job is to go to the forest approximately every two weeks to set up and collect pitfalls. Pitfalls are small plastic cups that are place at ground level and filled up with one-inch of soapy water. I pick up the pitfalls two days after I have set them up and I bring them to the microscope room in the Torrey lab to proceed with the identification. Then, I sort them out in three small tubes: ants, spiders and beetles. Ants have to be identified to the species level, while spiders are identified by genus, and beetles are archived for future investigations.