Fluctuations in Abundance of Tropical Insects

Abstract

Annual variability (AV), a measure for the fluctuation in abundance from year to year of insects in a given area, is defined as the variance of the distribution of log R, with R the net reproduction of a species. Some insect groups from two sites in Panama, one in a tropical forest, are compared with data from elsewhere in the world. The result is that insects from the wet tropics fluctuate about as much as their counterparts from the wet temperate zone. Hypotheses which predict greater stability (a lower AV of tropical insects) must be rejected, even for insects in a tropical forest. In areas with a relatively low and unpredictable rainfall, both tropical and temperate, AV tends to be larger. The data suggest that physical stability and predictability of the environment are important for determining the AV of the insects and that the wet but seasonal tropics are physically no more stable than the wet temperate zone. It is suggested that in nonseasonal tropics, should these exist, insect populations could be more stable.