Spatial and temporal patterns of colony density and habitat associations of a small desert ant

The abundance and distribution of ant colonies can be explained by several processes occurring before and after colony establishment, which potentially associate with natural and anthropogenic factors varying in time and space. We analyzed how the abundance and spatial arrangement of Pheidole bergi colonies varied according to habitat heterogeneity at two spatial scales and long-term environmental changes in the central Monte desert. Densities of active P. bergi colonies were similar in permanent grids within a protected algarrobal (open woodland) and on disturbed dirt roads crossing that habitat but showed a >50% reduction in the 2001–2025 period. There were also significant variations in colony density along some dirt roads, and they were 40–50% lower on those crossing other habitats (sand dunes and livestock-grazed algarrobal). Colonies within the algarrobal were not arranged randomly. The best-fitted of several spatial point process models proposed maximum probability of active colonies at the inter-patch borders of vegetation, decreasing 56% faster into the vegetated patches than towards the open patches. Further distance-related pairwise interactions between colonies were slightly positive in 2001, resulting in clumped distributions, and became strongly negative by 2019, when densities were less than a half, favoring more random and overdispersed spatial patterns. Pheidole bergi, a highly abundant and potentially ecologically significant ant species in the central Monte desert, seems flexible enough to establish colonies in different habitats and microhabitats although with distribution and population dynamics still shaped by environmental conditions such as soil texture, vegetation cover or resource availability. The strong decline in colony density along the years and associated changes in spatial distribution suggest that both direct and indirect effects of environmental variability, including prolonged drought, play a key role in the establishment and survival of its colonies. Furthermore, the shifting relevance of inter-colony interactions or density-dependent competition highlights the complex interplay between environmental constraints and intraspecific dynamics in the population ecology of P. bergi .