A wolf in fox's clothing? Using stable isotopes to quantify ecological replacement

Abstract

Ecological replacement as a conservation tool presupposes that nonnative taxa can restore degraded ecosystems by performing the ecological functions of extinct taxa. This assumption is rarely tested however, largely because it is difficult to quantify the functions of species extirpated long ago. Here, we test whether feral South American grey foxes (SAGF), introduced to the Falkland Islands ∼90 years ago, act as unintended ecological replacements for endemic Falkland Islands wolves (FIW), extirpated during the 19th century. Using hair stable isotope ratios as proxies for diet, we show that the isotopic niche space of modern SAGFs almost completely encompasses that of archaic FIWs. However, the former's niche is larger so while SAGFs may play similar ecological roles to FIWs, they probably perform additional functions, which may or may not be desirable. In so doing, we illustrate a generalized framework for using comparative isotopic niche analysis to test for ecological replacement objectively.