Spatial and temporal variations in the activity patterns of Mediterranean ant communities

We investigated the temporal and spatial separation of the activity rhythms of ants in three Mediterranean habitats. The different abilities of ant species to tolerate thermal stress influenced the time of day and year during which they were active. Activity of ants followed environmental fluctuations both seasonally and daily. Two groups of ant species could be distinguished in the communities studied: i) heat-tolerant species that were diurnal and changed little in daily activity rhythms throughout the year; ii) heat-intolerant species that shifted activity rhythms from diurnal to crepuscular-nocturnal at higher temperatures, and had peak activity at temperatures lower than 30°C. The different environmental conditions of each site affected the activity of different ant species and, therefore, community organization. In the forest areas, canopy cover created a heterogeneous environment of sunny and shaded areas throughout the day. Heat-intolerant species benefited from this spatial heterogeneity by lengthening their period of activity on hot days in areas covered by vegetation. This decreased the abundance of heat-tolerant species. Instead, in dry and open environments such as grasslands, the lack of trees caused the daily range of temperature to be sufficient to meet the requirements both of heat-adapted and cold-adapted species. This results in an increased diversity and a reduction in the dominance of heat-intolerant species.