Effects of an invasive ant and native predators on cotton rat recruitment and survival.

We used the imported red-ire ant (Solenopsis invicta; hereafter ire ant) and hispid cotton rat (Sigmodon hispidus) as model species to address the population-level effects of an invasive ant on a semiprecocial small mammal. We stocked cotton rats into 8 enclosures, implementing a 2-way factorial design with predator (ambient or excluded) and ire ant (ambient or reduced) treatments as factors. We trapped monthly from June 2012 to June 2013 and calculated monthly recruitment and survival. Rats in enclosures with ambient predators had a risk of mortality approximately 2 times greater than rats in enclosures with predators excluded. The risk of mortality was 3 and 4.5 times greater for female and male cotton rats, respectively, in enclosures with ambient ire ants and predators compared to enclosures with reduced ire ants and excluded predators. We found no effects on recruitment. Our results indicate that native predators had the greatest influence on cotton rat populations. Nevertheless, in the absence of other predators, the effects of ire ants on cotton rat survival are compensatory. [ABSTRACT FROM AUTHOR]