Evaluating anthropogenic influence on a mesopredator: opossum (Didelphis virginiana) isotope values influenced by corn agriculture more than urbanization

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Abstract
The composition of North American communities is changing due to anthropogenic land-use alteration. Mammalian mesopredators’ ability to consume anthropogenic trash due to their generalist diet has been referenced to partially explain their success in altered landscapes as they spread northward. We evaluated this assumption using carbon isotope values (δ13C) of the Virginia opossum ( Didelphis virginiana (Kerr, 1792)), a mesopredator expanding its range. δ13C values increase from consumption of C4 plants, including corn, a common food additive in North America. Opossum hairs from the Midwestern U.S. and Northeast were evaluated using generalized linear mixed models (GLMMs) to compare the predictive performances between winter harshness variables and anthropogenic variables. We also evaluated δ13C values through time to test if the temporal pattern of increased corn additives is mirrored in northern opossums. The best-performing GLMM included year and percentage corn fields as positive covariates. Variance in δ13C values increased exclusively in the “cornbelt” Midwest after 1970. δ13C values compared across space and time bolster evidence for the influence of agricultural development on the opossum’s range expansion.

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