Density and Spatial Distribution of Nests of Ectatomma ruidum and Pheidole fallax (Hymenoptera: Formicidae), as Response to the Recovery of Coal Mine Areas

Abstract

In this study, the spatial pattern of two ant species of different feeding habits, Ectatomma ruidum and Pheidole fallax (Hymenoptera: Formicidae) was assessed in rehabilitated areas of “Cerrejón” coal mine (Colombia). We tested whether there is a relationship between spatial distribution pattern, age rehabilitation and temporal changes. Three sites with different ages of rehabilitation (1, 9 and 20 years) and a secondary forest were sampled during dry and rainy seasons. Within four plots (6 x 40m) per site, we located, counted and estimated the minimum distance among nests. Our results indicated that the number of active nests varied according to sites and sampling season, E. ruidum had the highest density at both seasons, 166 nests ha-1 (forest) and 1333 nests ha-1 (9-y site). The nest density for P. fallax ranged between 125 and 625 nests ha-1 in the forest and the 20-y site, respectively, and at 1-year site ants were absent. Our results indicated that the nest distribution strongly depended on the scale of observation. A uniform distribution pattern was also found, mainly at the local scale (plot level), while an aggregated and random distribution was found at the site level. We conclude that ant density responded mostly to seasonal changes (dry versus wet season).

Impact of Pheidole fallax (Hymenoptera: Formicidae) as an Ecosystem Engineer in Rehabilitated Coal Mine Areas

“…Another possible explanation could be related to the size of the colony, although this was not evaluated. The high rate of soil turnover found in the study area [25] could explain why nests do not reach larger sizes. Some generalist ant species have been documented to not have a specific construction pattern, which would coincide with P. fallax presenting irregular patterns in the architecture of its nests, unlike fungus-eating ants, which build more elaborate and deeper nests than detritus-/seed-collecting ants [46].…”

“…It is important to highlight that the four additional years at the 20-year-old site are not the reason for the greater supply of resources. Maybe this difference is more related to better habitat conditions at the 20-year-old site, which promote the establishment of a greater number of nests both for this species [15,25] and for others [14,34]. Furthermore, species of the Pheidole genus have small foraging areas (±7 m) [35], which would indicate that the resources collected are close to where the nests are located.…”

“…Aspects of the biology of P. fallax have been described mainly in forest and agroecosystems. This work, along with that of other researchers [15,22,25], seeks to understand the role of this species in rehabilitated coal mine areas. The results of this study show that the bioturbation made by these ants can improve the soil conditions through nest building and maintenance, but also by accumulating organic debris.…”

“…Three plots (40 × 5 m) with a minimal distance of 300 m from each other were established in each site to locate nests of P. fallax. Following similar investigations [22,25], tuna baits (2 g) were placed in the soil in each plot in a 3 × 20 m grid. The ant workers that approached the baits were followed to identify the nest entrances.…”