Effects of More Frequent and Prolonged El Nino Events on Life-History Parameters of the Degu, a Long-Lived and Slow-Reproducing Rodent

Global climate change (GCC) can have profound effects on species whose ecology is governed primarily by climatic factors. The ecology of small mammals inhabiting semiarid Chile is strongly affected by the El Nino Southern Oscillation (ENSO). During La Nina events in this area, dry conditions prevail and species may disappear from the thorn-scrub habitat. Conversely, El Nino events bring high rainfall, and associated pulses of food trigger small-mammal population increases. We used capture-mark-recapture to study responses of the degu (Octodon degus), a dominant small mammal, to variation in rainfall over 18 years. In response to a recent trend toward wetter conditions, degus reached record-high densities and maintained more stable numbers in the area. Underlying mechanisms involved variation in adult survival, juvenile persistence, and fecundity linked to rainfall changes during consecutive years (i.e., rainfall phases). During prolonged droughts, degus had low survival and produced fewer offspring, with low persistence. Following high rainfall, these parameters reversed; consecutive wet years resulted in further increases. Weak declines in fecundity and adult survival and high persistence of juveniles explained delayed responses to deteriorating conditions in initial dry years. If GCC leads to increased frequency of El Nino events, we anticipate greater numerical dominance of degus in semiarid Chile and possible range expansion. Furthermore, degus have strong impacts on other small mammal and some plant species, are important prey species, and are agricultural pests and disease reservoirs. Hence, GCC has the potential to dramatically influence their ecology in northern Chile and to have cascading effects on other components of this system.