SPATIAL AND TEMPORAL VARIATIONS IN THE ACTIVITY PATTERNS OF MEDITERRANEAN ANT COMMUNITIES

We investigated the temporal and spatial separation of the activity rh ythms 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 envi ronmental fluctuations both seasonally and daily. Two groups of ant sp ecies could be distinguished in the communities studied: i) heat-toler ant species that were diurnal and changed little in daily activity rhy thms throughout the year; ii) heat-intolerant species that shifted act ivity rhythms from diurnal to crepuscular-nocturnal at higher temperat ures, and had peak activity at temperatures lower than 30 degrees C. T he different environmental conditions of each site affected the activi ty 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 be nefited from this spatial heterogeneity by lengthening their period of activity on hot days in areas covered by vegetation. This decreased t he abundance of heat-tolerant species. Instead, in dry and open enviro nments such as grasslands, the lack of trees caused the daily range of temperature to be sufficient to meet the requirements both of heat-ad apted and cold-adapted species. This results in an increased diversity and a reduction in the dominance of heat-intolerant species.