Diet overlap and competition among native and non-native small-bodied fishes in the Colorado River, Grand Canyon, Arizona.

摘要

Introductions of non-native fishes are threatening native fish communities in streams and rivers across the United States. The Colorado River especially has experienced numerous species invasions, and native fish populations throughout the basin are in decline. The native fish community in the Grand Canyon has been particularly affected, with half of the native fishes extirpated from the canyon. Many scientists blame interactions with non-native fishes for these declines. However, to date no one has conducted a thorough diet analysis of small-bodied fishes in the system to assess overlap between native and non-native fish diets. I analyzed the diets of native juvenile bluehead sucker, juvenile flannelmouth sucker, speckled dace, and non-native fathead minnow in multiple seasons and years. Small-bodied fishes in the Grand Canyon consumed a variety of resources, including diatoms, amorphous detritus, terrestrial vegetation, aquatic invertebrates, and terrestrial invertebrates. Diet composition depended on season, and was especially affected by turbidity during flood events. Generally, small-bodied fishes consumed more allochthonous carbon (e.g. amorphous detritus and terrestrial vegetation) during the monsoon season when tributaries were flooding and mainstem turbidity was high. Regardless of seasonal variability in diet, the juveniles of native suckers exhibited extensive diet overlap with non-native fathead minnows, but speckled dace diets did not overlap with fathead minnow diets. I therefore infer a potential for competition among fathead minnows and the juveniles of bluehead and flannelmouth suckers.