4.2 | Colorado Pikeminnow diet composition
Isotopic biplots between Colorado Pikeminnow and potential prey items corrected for trophic discrimination suggested our analysis incorporated most potential prey items (Figure 3). The mixing models resulted in substantial predicted overlap in the proportion each diet item was consumed within periods (Figure 4). However, Colorado Pikeminnow demonstrated a predicted increase in invertebrate consumption (probability = 0.94) from a historical median of 2.4% (95% CI = 0.0 – 30.5%) to a contemporary median of 24.9% (18.1 – 33.2%). The diet mixing models predicted Red Shiner (median = 28.4%, 95% CI = 10.6 – 41.6%) took the place of Fathead Minnow (29.0%, 2.7 – 68.6%) as the mostly highly consumed fish prey. Consumption of Flannelmouth Sucker and Speckled Dace, which was difficult to distinguish due to similar isotope values, averaged ~ 18% for each species and consumption by Colorado Pikeminnow may not have changed between periods (probabilities of 0.68 and 0.73, respectively). Prior to its extirpation and similar to other native potential prey, Roundtail Chub was predicted to have contributed ~18% (median = 17.9%, 1.5 – 53.7%) to Colorado Pikeminnow’s diet.