Efeito do clima, fogo e disponibilidade de alimento sobre a dinâmica populacional de Necromys lasiurus (Rodentia: Muridae) em uma área de savana Amazônica

Abstract

The population dynamics of Necromys lasiurus (Rodentia: Muridae) was studied in an isolated savanna area in the Alter do Chão region, Pará State, Brazil. Over 20 years, the number of individuals captured decreased from 20 to 1 in one plot. A similar decrease occurred in 39 plots distributed in all savannas in the area from 2000 to 2006. The decreases in the long and short terms were associated with Southern Oscillation Index (SOI). This index is related to the intensity of global climatic events (El Niño/La Niña), which affect the intensity of the dry seasons. If the environmental conditions do not change, linear models indicate that the local N. lasiurus population could go to extinction within 5 years. Analyses of stable isotopes of carbon (13C) and nitrogen (15N) indicate that N. lasiurus is a generalist whose diet did not varies among individuals of different sizes or between sexes. The diet of N. lasiurus varies with the availability of food sources (grasses and dicotyledons). Savanna fires changed the quality of available food and induced a change in trophic level due to a lesser intake of food from food chains based on dicotyledons and a consequent higher ingestion of items from food chains based on grasses and invertebrates. However, the change in the diet did not compensate completely the lack of food items from de dicotyledon food chains, because the change was associated with a smaller index of populational increase, probably due to a smaller intake of carbohydrates in the reproductive season. The mean capture rate of N. lasiurus in the region decrease during the study. However, the sample plots were distributed in one large area of savanna and three small isolated patches of savanna. The synchrony in populational dynamics of the specie was related to the linear distance between sample sites. While the large savanna and two of the smaller areas showed a largely synchronous decrease in the capture rate of individuals, in the other area the capture rate was relatively stable abundance over six years. The plot that did not suffer a decrease may be a source of individuals to recolonize the other areas, reducing the probability of local extinction of N. lasiurus. Nevertheless, populational rescue in the other areas probably will be effective only if there is a reduction in fires frequency and concomitant decrease in the intensity of dry seasons.