Ants show collective and individual behavioural flexibility in their response to immediate context, choosing for example between different foraging strategies. In Pachycondyla striata, workers can forage solitarily or recruit and guide nestmates to larger food sources through tandem running. Although considered more ancestral and less efficient than pheromone trail-laying, this strategy is common especially in species with small colony size. What is not known is how the decision to recruit or follow varies according to the immediate context. That is, how fine adjustments in information transfer affect immediate foraging decisions at the colony level. Here, we studied individually marked workers and evaluated their foraging decisions when food items varied in nature (protein vs carbohydrate), size, and distance from the nest at different temperatures and humidity levels. Our results show that tandem run leaders and potential followers adjust their behaviour according to a combination of external factors. While 84.2% of trips were solitary, most ants (81%) performed at least one tandem run. However, tandem runs were more frequent for nearby resources and at higher relative humidity. Interestingly, when food items were located far away, tandem runs were more successful when heading to protein sources (75%) compared to carbohydrate sources (42%). Our results suggest that the social information transfer between leaders and followers conveys more information than previously thought, and also relies on their experience and motivation.

With urbanization increasing globally, conservation ecologists need to characterize the functioning of ecosystems embedded in urban landscapes. Ubiquitous and hyperdiverse, ants are an ideal model taxon for this purpose. Here we compared diversity, richness, and abundance of ants in a forest fragment and a green urban area within the City of São Paulo, characterizing relationships among ant species. We found higher species abundance and richness in the urban area, whereas diversity was greater in the secondary forest fragment. Transect sampling revealed higher heterogeneity in the more urban area, with a number of species not found in the secondary forest. Bait sampling suggested that, in the urban area, dominance of one or a few species was stronger than in the secondary forest, possibly because dominant species outnumbered other species at resources and behaved aggressively. We found that a limited number of species dominated in both the forest and the urban area. Although this study only relies on a limited sample size taken in relatively narrow geographic and climatic conditions, it suggests that ant community traits in urban environments vary depending on human-related disturbance.

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