Ecological role of an apex predator revealed by a reintroduction experiment and Bayesian statistics

Abstract

Recent studies suggest that apex predators play a pivotal role in maintaining healthy, balanced ecosystems. However, a criticism of studies investigating the ecological role of apex predators is that understanding does not come from manipulative experiments. Here, we use a before-after-control-impact-paired design to test predictions generated from trophic cascade theory (TCT) and mesopredator release hypothesis (MRH) by experimentally introducing dingoes into a 37-km2 paddock and measuring the resultant effects on mammal assemblages. To increase precision of parameter estimates generated by our experiment, we used a Bayesian framework which included prior information recorded from a mensurative study located in a comparable ecosystem that contrasted indices of mammal abundance where dingoes were common and rare. Results of the mensurative study were consistent with TCT and MRH. When using an uninformative prior, results of the experiment showed that dingo addition only had a negative effect on kangaroo activity. Use of an informative prior reduced uncertainty of the posterior mean parameter estimates from the experiment and suggested that red foxes were affected negatively and small mammals and rabbits were affected positively by dingo introduction. However, the prior had a strong influence on the posterior mean effect sizes for small mammals, rabbits and foxes. Opposite polarity of uninformed and prior parameter estimates for rabbits suggests that the prior was incompatible with the uninformed estimates from the manipulative experiment. Our study shows how use of logical informative priors can help to overcome statistical issues associated with low-replication in large-scale experiments, but the strong influence of the prior means that our findings were driven largely by the mensurative study.