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Different aspects of the foraging strategies of two harvester ant species, Messor wasmanni and M. minor, were investigated in a Mediterranean dry grassland area. Baits were used to evaluate the existence of a trade-off between resource discovery and domination as well as the effect of three variables (air temperature, relative humidity and distance) on the trade-off. Baits were also utilized to explore random vs non random use of time by colonies. Random vs non random utilization of space was instead evaluated by mapping the daily foraging area of colonies in a grid of 900 plots of 1 m2 each. Results revealed that species coexistence is not preferentially supported by a trade-off in resource utilization with no overall effect of the examined variables. The foraging activity of the two species widely overlapped whilst a clear competition for space occurred. The observed space partitioning could represent an advantageous strategy for the coexistence of the two ant species. © 2014 Springer Science+Business Media New York

The Argentine ant, Linepithema humile, is an invasive species widespread in the Mediterranean climatic regions of the world, which is well demonstrated to have a negative impact on native ants and on the community structure. At the beginning of the twentieth century its presence was recorded for the first time in Italy and currently is mainly found along the Tyrrhenian coast, where it locally shows a patchy distribution. In our study we investigated an environmentally homogenous transect including an invaded area and a control zone inside the Presidential Estate of Castelporziano, to evaluate possible impact of the Argentine ant on the native species and differences in ant community composition. For our purpose we used pitfall traps and an active field sampling along the transect, with six replicates from April to August 2015. The sampling indicated a significant reduction of the number of species in the invaded area, while the multivariate analysis and the percentage of species in both the zones showed a different ant community composition between invaded and uninvaded areas. These findings were also supported by very different values of the diversity indices calculated for each zone and the lower number of functional groups found in the invaded area. According to literature, we conclude that L. humile could be the species mainly responsible for this arrangement. Future study using a higher spatial scale and covering a larger variety of habitats is certainly required.

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