The Effects of Crayfish Predation and Vegetation Cover on Tadpole Growth, Survival, and Nonlethal Injury
Predator–prey interactions play an important role in structuring larval anuran communities in ephemeral wetlands. The type of interaction often depends on the predator species and the complexity of the aquatic habitat. We experimentally evaluated the effects of Panhandle Crayfish (Procambarus evermanni) predation on larval Southern Leopard Frogs (Lithobates sphenocephalus) and larval Ornate Chorus Frogs (Pseudacris ornata). We performed separate experiments for each anuran species and used multiple vegetation treatments to examine whether vegetation could provide refugia from crayfish predation. Our results indicate that crayfish are effective predators of anuran larvae regardless of the amount of vegetation present. Encounters between tadpoles and crayfish often resulted in nonlethal tail injury for tadpoles, suggesting that crayfish predation is prominent in ephemeral wetland communities. Leopard frog tadpoles in predator treatments also grew larger than their counterparts in nonpredator treatments, suggesting a reduction in intraspecific competition. Reduced competition and higher growth rates may allow anuran larvae to develop and metamorphose faster, allowing them to escape aquatic predators, drying wetlands, or both.Abstract
Mean number of surviving Southern Leopard Frog (Lithobates sphenocephalus) tadpoles (A) and mean tadpole SVL (B,C) over time in a mesocosm experiment with six treatments: high vegetation (68% coverage) with and without a predator, low vegetation (34% coverage) with and without a predator, and no vegetation with and without a predator. A single Panhandle Crayfish (Procambarus evermanni) was present in the predator treatments. Plots show tadpole survival and SVL calculated across vegetation (A,B) and predator treatment groups (C), as there were no significant interactions between vegetation and predator. Asterisks represent weeks when significant differences in survival or SVL were identified. For panel C, these differences occurred only between the low vegetation and no vegetation treatments. Error bars represent standard error.
Frequency of tail injury to Southern Leopard Frog (Lithobates sphenocephalus) tadpoles in mesocosms containing a single Panhandle Crayfish (Procambarus evermanni). Mesocosms with a crayfish had three different amounts of herbaceous vegetation coverage: high (68% coverage), low (34% coverage), and no vegetation. By week 10, a significantly higher percentage of tadpoles with tail injury occurred in the no vegetation treatment than in the high vegetation treatment. Error bars represent standard error.
Mean number of surviving Ornate Chorus Frog (Pseudacris ornata) tadpoles in four treatments including high vegetation (80% coverage) with and without a predator and low vegetation (40% coverage) with and without a predator. A single Panhandle Crayfish (Procambarus evermani) was present in the predator treatments. Asterisks represent weeks when there were significantly more tadpoles alive in nonpredator treatments compared to predator treatments. There were no significant effects of vegetation level on tadpole survival. Error bars represent standard error.
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