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Long-Term Variation in Small Mammal Abundance in Forest and Savanna of Bolivian Cerrado

Emmons, Louise H.
Biotropica 2009 v.41 no.4 pp. 493-502
Cavia, El Nino, burning, cerrado, dew, drought, dry season, fauna, forests, habitats, herbivores, insectivores, national parks, night temperature, rain, rodents, savannas, small mammals, smoke, Bolivia
Small mammals were trapped annually in two savanna and two forest plots in cerrado habitats of Noel Kempff Mercado National Park, Santa Cruz, Bolivia, for 5-10 yr. Eighteen species were captured in forest and seven species in savanna. Species numbers and total number of individuals captured were tightly correlated. In forest, species and abundance varied interannually by up to fourfold in one plot and to 100-fold in the other, and showed alternating highs and lows as is typical for small mammals. The largest faunal differences were due not to site differences, but to year differences, with markedly different patterns in forests and savannas. Abundance was not correlated with rainfall overall, but showed correlation in exceptional years of rainfall and ENSO drought. In savanna, species and overall abundance declined without recovery during 3 yr after reaching minimum numbers in 2004. One species, Cavia aperea, became extinct on both plots, and subsequently, apparently on the entire savanna. Both herbivorous and insectivorous species declined together. Rainfall, fire, and flooding do not seem to account for savanna rodent declines. I propose the novel hypothesis that smoke from anthropogenic burning raises nocturnal temperatures and prevents dew formation, and that a decrease in nightly dry season dewfall has been instrumental in rodent declines. Anecdotal and climatic data are consistent with this hypothesis, but it cannot yet be tested.