Honors College Thesis


Variation of the Trowbridge's shrew (Sorex trowbridgii) diet across forest types in the Oregon Cascades Public Deposited

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  • Investigating the insectivorous diet of the Trowbridge’s shrew (Sorex trowbridgii) across forest types can illustrate how forest management affects biotic communities. I used DNA metabarcoding methods with ANML primers to identify stomach and intestines contents from shrews caught in pitfall traps in the HJ Andrews Experimental Forest (HJA) and Willamette National Forest in the Oregon Cascades. I caught 54 Trowbridge’s shrews between July and September of 2018 and identified diets from 37 shrews (12 intestines, 35 stomachs). Shrew diet consisted of Orthoptera, Lepidoptera, Diptera, Araneae, and Scolopendromorpha. Specifically, Tettigoniidae were consumed most consistently (FOO = 0.41) and constituted a large portion of the diet (mean RRA = 0.39). When comparing the mean relative read abundance of taxonomic orders against site variables, more Lepidoptera were consumed outside of HJA (t10= -2.445, P = 0.03) and more Araneae were consumed at mid elevations than low elevations (t5 = 2.229, P = 0.08). Although Trowbridge’s shrew diets were similar across forest types, I found that they consumed more species in recently disturbed areas and areas lacking old-growth characteristics. This suggests shrews have a more diverse diet in younger stands. Further research should be done to assess the species’ fitness in different forest types.
  • Key Words: Sorex trowbridgii, Oregon Cascades, metabarcoding, diet analysis, forest management
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