El Nino events, precipitation patterns, and rodent outbreaks are statistically associated in semiarid Chile

In the last two decades, several researchers have noted rodent population o utbreaks in semiarid South America, in association with unusually high prec ipitation that seemingly concurs with Ei Nino events. To date, no studies h ave been conducted to determine the statistical relationships between ENSO (El Nino Southern Oscillation) events. increased precipitation, and rodent irruptions. Here we show that: 1) there is a statistical association betwee n ENSO events and increased precipitation in the semiarid region of norther n Chile, 2) the occurrence or rodent outbreaks in that region is statistica lly related with the precipitation levels of the same year; 3) the multi-an nual patterns of the total annual precipitation levels and population abund ance of those rodents Juring the summer are positively associated. The puta tive chain of effects seems to start with unusually high rainfall brought b y ENSO to semiarid environments. which thus respond with increased primary productivity (herbage and seeds), which then fuels the rodent outbreaks.