Inferring Vulnerability to Introduced Predators without Experimental Demonstration: Case Study of Suter's Skink in New Zealand

Abstract

Abstract: The coast‐inhabiting Suter's skink ( Oligosoma suteri ) has a fragmented distribution on islands around northern New Zealand, which has been attributed to the effects of introduced predators. We used classification trees to assess a range of factors that might influence the distribution of Suter's skinks. We then assessed the vulnerability to predation of juvenile and adult Suter's skinks by using a population viability analysis ( PVA ) model. We tested predictions from the classification tree and PVA models on two islands from which introduced Pacific rats ( Rattus exulans ) were removed. On one island, Suter's skinks were reintroduced ( assuming previous extirpation by rats ), and on the other the skinks had survived in the presence of Pacific rats. Our results revealed that populations of Suter's skinks are likely to be susceptible to predation where there are no bouldery beaches as refuges. Where these beaches are present, they are likely to function as refuges only if there is effective protection for adults. We conclude, however, that despite some apparently compelling circumstantial evidence of the effects of introduced predators on New Zealand lizards, it appears impractical to verify cause and effect with field manipulations if lizards and introduced predators do not already coexist.