Ant species distribution along a topographic gradient in a "terra-firme" forest reserve in Central Amazonia

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 km 2 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.

A comparison between time of exposure, number of pitfall traps and the sampling cost to capture ground-dwelling poneromorph ants (Hymenoptera: Formicidae)

“…In total 750 samples were taken from 25 pitfall traps installed at 10 m intervals in each plot. We also used data from Oliveira et al (2009), which used the same pitfall traps in the same period and area but with a different sampling effort, using a total 300 samples taken from 10 pitfall traps installed at 25 m intervals in each plot and left open for 48 hours. Thus, using data from both surveys, we are analyzing three sampling efforts in the 30 plots: two days and 300 traps, 14 days and 300 traps, 14 days and 750 traps were considered as the minimum, intermediate and maximum effort, respectively.…”

“…In tropical rainforest, soil clay content has also been shown to affect the distribution of palms (Costa et al, 2009), frogs (Menin et al, 2007), oribatid mites and ants (Oliveira et al, 2009;Vasconcelos et al, 2003;Souza et al, 2007;2016). The effect of each environmental factor varies depending on the scale of analysis (total area surveyed and the number of sampling units).…”

“…Traditionally, pitfall traps remain in the field for 48 hours in studies with ground-dwelling ants (Pik et al, 1999;Bestelmeyer et al, 2000;Vasconcelos et al, 2003;Oliveira et al, 2009;Souza et al, 2009;Baccaro et al, 2012Baccaro et al, , 2013Souza et al, 2012). Nevertheless, it is argued that the permanence of the traps for longer periods could capture more diversity (Bestelmeyer et al, 2000).…”

“…These combinations of environmental variables account for the variation associated with ant's assemblage structure across tropical landscapes (Vasconcelos et al, 2003;Oliveira et al, 2009). Investigating these types of relationships between ants and environmental variables is of more practical importance than simply showing correlations between the numbers of taxonomic entities (Souza et al, 2016).…”

The Need for Large-Scale, Integrated Studies of Biodiversity - the Experience of the Program for Biodiversity Research in Brazilian Amazonia

“…For palms, soil and topography could explain 60 to 73% of the variance in species composition ). For ants, soil texture could predict 3 to 31% (depending on the collection method) of species composition (Oliveira et al 2009). Some biological groups, such as pseudo-scorpions (Aguiar et al 2006), were not associated with soil and topography, and the tight control on plot environmental conditions means that these results are not artifacts of sampling.…”