Shelter is a crucial component to many species' survival, and when shelter becomes limited, resulting competition can have negative effects on growth and survival. In Little Chucky Creek, a tributary to the Nolichucky River in Tennessee, the severe population decline of the Chucky Madtom Noturus crypticus has been partially attributed to an increase in the abundance of cavity-dwelling crayfish following the establishment of two nonnative species. While it has been suggested that the crayfish exclude the cavity-dwelling fish from shelter, we are not aware of studies that have been conducted to demonstrate that crayfish directly outcompete madtoms in this regard. Our objective was to experimentally test the hypothesis that shelter competition between crayfish and the Mountain Madtom N. eleutherus, a surrogate species for the Chucky Madtom, is a function of relative size. Behavioral trials were conducted in which shelter was the limited resource for the two potential competitors. The madtoms' success at occupying the provided cover object was recorded for 5 days as well as health condition at the end of the competition phase. Both madtom occupancy and health condition were positively correlated with increasing relative size. As the size differential increased between madtoms and crayfish, madtoms were more successful at occupying the cover object, and overall condition was greater at the end of the trial. Conversely, when madtoms were smaller than crayfish, individuals were more commonly excluded from the cover object or even killed. Juvenile madtoms experienced 100% mortality. We concluded that crayfish exhibit a size-specific competitive advantage over Mountain Madtoms when shelter is limited, and that crayfishes may catalyze fish population declines at least partially through shelter exclusion and predation on juveniles.
Size-specific Advantage in Shelter Competition between the Mountain Madtom and Crayfishes
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Meredith H Harris, Kristin I Womble, J Brian Alford; Size-specific Advantage in Shelter Competition between the Mountain Madtom and Crayfishes. Journal of Fish and Wildlife Management doi: https://doi.org/10.3996/042019-JFWM-023
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