We report on the population response of a species of rodent, Necromys lasiurus, to southern oscillation index (SOI) and extent of regional fire in an Amazonian savanna. Information on temporal variation in local abundance of N. lasiurus in a 4.0 ha savanna plot was obtained from 1985 to 1989, from 1997 to 1998 and 2000–2006, giving data on 14 of the 22 years. Throughout this period, rodent density declined by 90%. Densities were positively associated with SOI and the extent of fire in the region. Rainfall was related to SOI and negatively influenced the extent of fire. However, the amount of rain had no measurable direct effect on rat densities. Thus, small changes in temperature, and consequently fire probability and intensity, may have drastic consequences on the biota of Amazonian savannas, especially in El Niño periods.
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