Abstract
In Amazonia, topographical variations in soil and forest structure within "terra-firme" ecosystems are important factors correlated with terrestrial invertebrates' distribution. The objective of this work was to assess the effects of soil clay content and slope on ant species distribution over a 25 km² grid covering the natural topographic continuum. Using three complementary sampling methods (sardine baits, pitfall traps and litter samples extracted in Winkler sacks), 300 subsamples of each method were taken in 30 plots distributed over a wet tropical forest in the Ducke Reserve (Manaus, AM, Brazil). An amount of 26,814 individuals from 11 subfamilies, 54 genera, 85 species and 152 morphospecies was recorded (Pheidole represented 37% of all morphospecies). The genus Eurhopalothrix was registered for the first time for the reserve. Species number was not correlated with slope or clay content, except for the species sampled from litter. However, the Principal Coordinate Analysis indicated that the main pattern of species composition from pitfall and litter samples was related to clay content. Almost half of the species were found only in valleys or only on plateaus, which suggests that most of them are habitat specialists. In Central Amazonia, soil texture is usually correlated with vegetation structure and moisture content, creating different microhabitats, which probably account for the observed differences in ant community structure.
Highlights
One third of the animal biomass in Amazonian “terra‐firme” forests is composed by ants and termites (Fittkau & Klinge, 1973), and one hectare could contain more than eight million ant individuals and one million termite individuals (Hölldobler & Wilson, 1990)
Studies using ants or other terrestrial invertebrates at the Ducke Reserve, a 10,000‐ha “terra‐firme” forest reserve close to Manaus which has been intensively studied in the last 40 years, were normally targeted on small‐scale distributions (Beck, 1968; Penny & Arias, 1982), and basic management questions about how these animals respond to environmental gradients remain unanswered
The objective of this work was to assess the effects of soil clay content and slope on ant species distribution along a topographic gradient in a mesospatial scale (25 km2) at the Ducke Reserve, Manaus, AM, Brazil
Summary
One third of the animal biomass in Amazonian “terra‐firme” forests is composed by ants and termites (Fittkau & Klinge, 1973), and one hectare could contain more than eight million ant individuals and one million termite individuals (Hölldobler & Wilson, 1990). Studies using ants or other terrestrial invertebrates at the Ducke Reserve, a 10,000‐ha “terra‐firme” forest reserve close to Manaus which has been intensively studied in the last 40 years, were normally targeted on small‐scale distributions (Beck, 1968; Penny & Arias, 1982), and basic management questions about how these animals respond to environmental gradients remain unanswered. In Central Amazonia, the topographic gradient is correlated with soil characteristics, creating a gradient with sandy soils in the valleys and clay soils on the plateaus (Chauvel et al, 1987). Soil traits, such as soil clay content, are correlated with moisture content, with poorly drained areas concentrated on valleys and relatively dry areas concentrated on plateaus (Ranzani, 1980). Litter is an important resource for nesting sites and food, and, in conjunction with moisture availability, it can generate microhabitat variability, which may affect demographic patterns in ground‐dwelling ant assemblages (Vasconcelos et al, 2003)
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