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

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)

Efecto del tamaño de la ronda hidráulica sobre las comunidades de escarabajos coprófagos (Scarabaeidae: Scarabaeinae) en la cuenca media y baja del rio Cesar, Colombia.

Se analizó el efecto del tamaño de la ronda hidráulica de los bosques riparios en la comunidad de escarabajos coprófagos en dos hábitats (Potrero y Bosque), en cinco estaciones en la cuenca del Rio Cesar (Colombia). Por hábitat se marcaron ocho puntos distanciados 50 m, colocándose en cada punto una trampa de caída cebada con excremento humano. Se capturaron 5 072 individuos agrupados en 11 géneros y 20 especies, de las cuales, las más abundantes fueron Pseudocanthon perplexus y Onthophagus marginicollis. Los fragmentos de bosque fueron más diversos que los potreros, mientras que los fragmentos de bosque con mayor ronda hidráulica fueron más diversos que los pequeños; demostrándose la respuesta de los Scarabaeinae a la fragmentación de los bosques tropicales

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

Pheidole fallax is one the most abundant ants in sites where coal mines have undergone rehabilitation and in forests without mine intervention. The impact that this species may have as an ecosystem engineer needs to be assessed. We aimed to test whether P. fallax nests have an effect on soil chemical properties, to characterize the organic debris found in the refuse piles, and to describe nest architecture as proxy of the bioturbation effect. The study was carried out in a coal mine in Colombia, in sites with 16 and 20 years of rehabilitation. Samples were taken from inside the nests, from the external refuse pile, and from a control treatment one meter away from the nest. The three sample types were subjected to chemical analysis and near-infrared spectra (NIRS). The biomass of items from the 20-year site was significantly greater, and P. fallax use food resources of different trophic levels, with arthropods and seeds being the main items in their diet. The NIRS analysis enabled us to distinguish the origin of the sample: refuse pile, interior of nest, or control soil. No statistical differences were found between the soil of the nests and control soil. High contents of organic matter and other parameters contributed to the soil nutrient pool through accumulation of organic debris in the refuse piles. Nest molds presented an asymmetric architecture, with mean volume ranging from 30 to 105.7 cm3 and an average of 11.8 chambers per nest. The construction and maintenance of nests may play an important role in the reestablishment of ecological and hydrological processes, such as bioturbation and water infiltration, respectively