Fig. 1 Results of null model analyses. A. Values of the Shannon Diversity Index increased with increasing diet breadth (Kruskal-Wallis:X² = 974.05, df = 8, P < 0.001). B. There was no significant relationship between diet breadth and standardized values of Shannon Evenness (Kruskal-Wallis:X² = 13.99, df = 8, P = 0.08).

A total of 14 T. striatus and 11 N. minimus were tested. One N. minimus trial was removed from the Evenness analysis because the chipmunk only consumed a small amount of a single seed type, so the value of the Shannon Index was zero, and the Evenness was mathematically undefined. If individuals consumed resources in their offered proportions, we expect the Shannon Diversity Index (H_s ) to be 0.70. In the absence of seed preference, we expect the Shannon Evenness (J’ ) to be 0.43. We found that both T. striatus (H_s = 0.41 ± 0.03; One-sample t test: t ₁₃ = -10.56,P < 0.001) and N. minimus(H_s = 0.38 ± 0.06; One-sample t test:t ₁₀ = -4.94, P < 0.001) had values for the Shannon Index that were significantly lower than expected. Similar results were obtained for our analysis of Shannon Evenness (T. striatus : J’ = 0.28 ± 0.01; One-samplet test: t ₁₃ = -10.39, P < 0.001; N. minimus : J’ = 0.29 ± 0.02, One-sample ttest: t ₉ = -6.02, P < 0.001). Both of these results indicate evidence of significant seed preferences by both chipmunk species.

A repeated measures analysis compared the proportion consumed of each seed species between T. striatus and N. minimus to account for the fact that the consumption of each seed was not independent in this study. If the species of chipmunk is not accounted for, there is no significant difference between the seed species and proportion consumed (ANOVA: F _4,92 = 0.73, P = 0.57). However, there is a significant interaction between chipmunk species and seed species (ANOVA: F _4,92 = 16.07, P< 0.001). This indicates that the identity of seed consumed the most depends on the chipmunk species, thus confirming the results of the Shannon Evenness t-tests even after accounting for the fact that the consumption of seed species is not independent.