Fig 1.
The Smith River watershed in central Montana. Sampling reaches are denoted by grey circles. Graphic created using ESRI software (Redlands, CA) and open-access data from the Montana State Library including Montana Major Streams and Lakes (1993) and Grayscale Shaded Relief Image of Montana, 30-meter (2002).
Fig 2.
Diet categories grouped by order.
Standard boxplots showing proportions of diet item from the specified category found in mountain whitefish (MW) and rainbow trout (RB) in Sheep Creek and the Smith River. Panels show proportions of (A) Diptera; (B) Ephemeroptera; (C) Trichoptera; (D) Oligochaeta; and (E) any other taxa pooled. Box ends represent the 25th and 75th quantiles, horizontal lines are the medians, the upper whisker extends to the largest observation no further than 1.5 × interquartile range (IQR) from the 75th quantile, and the lower whisker extends to the smallest observation no further than 1.5 × IQR from the 25th quantile.
Fig 3.
Diet categories grouped by family.
Boxplots showing proportions of diet items from the specified category (family) found in mountain whitefish (MW) and rainbow trout (RB) diets in Sheep Creek and the Smith River. Panels show proportions of (A) Athericidae; (B) Baetidae; (C) Brachycentridae; (D) Chironomidae; (E) Ephemerellidae; (F) Heptageniidae; (G) Hydropsychidae; and (H) all other taxa pooled. Box ends represent 25th and 75th quantiles, horizontal lines are the medians, the upper whisker extends to the largest observation no further than 1.5 × interquartile range (IQR) from 75th quantile, and the lower whisker extends to the smallest observation no further than 1.5 × IQR from 25th quantile.
Table 1.
Models of eight most consumed diet categories.
Summary of model results for the eight most commonly consumed diet categories. Dashes indicate parameters that were not included in the final model. Coefficient estimates, in the first column under each explanatory variable, are reported on the log-odds scale. Baseline categories were Sheep Creek for the stream variable and mountain whitefish for the species variable. Adjusted deviance explained for each model was Athericidae = 0.40, Baetidae = 0.40, Brachycentridae = 0.32, Chironomidae = 0.52, Ephemerellidae = 0.08, Heptageniidae = 0.19, Hydropsychidae = 0.57, and Oligochaeta = 0.56.
Table 2.
Estimated food item proportions.
The estimated proportions of total food items in the diets of mountain whitefish and rainbow trout in the Smith River and Sheep Creek by taxon. Estimates are derived from generalized linear models, and confidence intervals (95%) are shown in parentheses. Only the eight most common taxa in fish diets are listed.
Table 3.
Pianka’s index of niche overlap comparing diets of mountain whitefish and rainbow trout in Sheep Creek and the Smith River. Values ≥ 0.60 indicate high diet overlap.
Fig 4.
Feeding strategy diagram. Feeding strategy diagram of the modified Costello method according to Amundsen et al. (1996) [31]. Prey-specific abundances and frequencies of occurrence in the diets of mountain whitefish (MW) and rainbow trout (RB) in the Smith River and Sheep Creek. Numbered diet categories are 1: Fish larvae; 2: Coleoptera; 3: Amphipoda; 4: Scorpaeniformes; 5: Hemiptera; 6: Gastropoda; 7: Diptera pupae; 8: Oligochaeta; 9: Acari; 10: Neuroptera. Panels show (A) rainbow trout in the Smith River; (B) rainbow trout in Sheep Creek; (C) mountain whitefish in the Smith River; and (D) mountain whitefish in Sheep Creek.
Fig 5.
Prey-item richness (i.e., number of unique prey-items) in the diets of mountain whitefish (MW) and rainbow trout (RB) in the Smith River and Sheep Creek. Box ends represent 25th and 75th quantiles, horizontal lines are the medians, the upper whisker extends to the largest observation no further than 1.5 × interquartile range (IQR) from 75th quantile, and the lower whisker extends to the smallest observation no further than 1.5 × IQR from 25th quantile.