We searched extensively for Pogonomyrmex spp. colonies in ~15 ha of algarrobal during four times (October, December, February and April) of three consecutive growing seasons. Colonies were marked permanently with a numbered stick and mapped; colonies on dirt roads or roadsides were ignored. During each sampling period all previously detected colonies were checked, recording their status (with or without external activity) and, if they have moved the colony entrance, the distance of its displacement. Any colony >5 m from any previously detected colony was considered a new colony. Inactive colonies were checked in the following sampling periods (including the summer 2002-2003) and considered “dead” if they showed no further external activity. The number of active Pogonomyrmex colonies within the algarrobal varied within and between consecutive activity seasons, appearing and disappearing or moving their nest entrances quite frequently. Almost half of the ~15 ha sampled had no active colonies during those three years, and P. rastratus [propinqua] accounted for almost half of them. Distance to dirt roads was a strong predictor of the heterogeneous density of Pogonomyrmex colonies: sectors close (<50 m) to dirt roads concentrated almost all colonies. As a consequence, all three species were spatially aggregated, but while two of them (P. mendozanus and P. inermis) occurred in patches, P. rastratus was a bit more extended. Species were spatially segregated, particularly P. rastratus with P. inermis.

Autores Jhon Maurat - Geanella Ramon Actividad Autónoma 2 Business Analytics

Creating priors from thin air

Colonies of the harvester ants in the Pogonomyrmex genus appeared rather homogeneously along the dirt roads crossing the algarrobal of Ñacuñán (Mendoza, Argentina) in the central Monte desert, but each of the three species showed intraspecific patterns of aggregation, and interespecific pattern of segregation between pairs of species, which resulted in 3–7 patches per species along each 1.5 km segment censused. These patched distributions probably result from species-specific responses to variable environmental conditions along the roads: soil permeability and relative altitude (which are partially correlated). P. inermis selected more impermeable (clayish) soils that tend to accumulate in relative depressions, and P. mendozanus more permeable (sandy) soils which predominate in relative highs. P. rastratus [propinqua] is more broadly distributed, asociated with the intermediate conditions typical of the algarrobal. The habitat associations and the resulting spatial patterns of each Pogonomyrmex species along the dirt roads persisted in time in spite of strong declines in the density of active nests of the three species (particularly PR) between 2004 and 2010.

Objetivo 1 del Proyecto II de Ciencia de Datos de la UPV sobre la influencia del nivel de desarrollo económico en los hábitos alimentarios de los ciudadanos