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
(Hs ) 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 (Hs = 0.41 ±
0.03; One-sample t test: t 13 = -10.56,P < 0.001) and N. minimus(Hs = 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.