Cranial morphological scaling and relative prey size limitations for a native predator in an invaded system
Over evolutionary time, predator-prey interactions have shaped and constrained functional and behavioral traits of piscivorous fishes. The endangered Colorado Pikeminnow Ptychocheilus lucius, a large endemic piscivore of the Colorado River Basin, encounters a substantially altered prey base that differs in behaviors and morphologies compared to the historical suite of native prey. To assess physical limitations of Colorado Pikeminnow predation, we conducted a feeding experiment with two species of nonnative prey (spined and despined Channel Catfish Ictalurus punctatus and Red Shiner Cyprinella lutrensis) and quantified scaling of cranial morphology in this predator. In our predation experiments, Colorado Pikeminnow (215–312 mm total length) consumed both spined and despined Channel Catfish as well as Red Shiner but only consumed prey less than 20% of the predator’s total length. Previous feeding trials using smaller Colorado Pikeminnow, with native and nonnative prey species, indicated they consumed prey up to 35% of their total length, suggesting relative prey size limits may decrease as this predator grows. Morphological measurements also suggested relative prey size suitability may decrease as Colorado Pikeminnow become larger, with head depth and width demonstrating isometric scaling at small sizes and shifting to negative allometry as fish get larger. Together, these data suggest an ontogenetic shift in the head morphology of Colorado Pikeminnow may decrease the relative size of prey available to these predators. In severely altered systems, understanding trophic characteristics that limit overall predator resource availability will be critical for conservation of piscivorous fishes.
KeywordsEndangered piscivore Feeding ecology Morphological ontogeny Prey limitations
We thank S. Walker, Assistant Project Leader Inks Dam National Fish Hatchery, who provided Channel Catfish used in feeding experiments and M. Ulibarri, Supervisor Southwestern Native ARRC, who provided Colorado Pikeminnow. We thank personnel from NMFWCO, which included but was not limited to, A. Dean, W. Furr, D. Myer, C. Kitcheyan, and R. Ulibarri who assisted in fish husbandry, feeding experiments, and morphological assessment. We also thank A. Snyder, Division of Fishes Collections Manager Museum of Southwestern Biology, for accession of Colorado Pikeminnow specimens. We thank T. Diver for the Colorado Pikeminnow photographs. Lastly we thank, M. Dela Cruz and D. Propst for helpful comments on prior versions of this manuscript. Experimental use of federally listed Colorado Pikeminnow was conducted with U.S. Fish and Wildlife Service Permit No. TE676811-3. Mention of MS222 and R statistical language does not constitute endorsement by U.S. Fish and Wildlife Service.
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