The preference in seed selection by Messor capitatus (Latreille) was studied with artificial seeds (weighted styropore spheres) in the laboratory and with natural seeds in the field. The laboratory experiments showed no strong preference for size of the artificial seeds in the range 3–8 mm (diameter). A mass of about 400 mg was selected when artificial seeds of 5‐5.5 mm were offered at different distances from the nest.
In the field experiments, crushed seeds were placed 2 m from the nest and ants showed a clear preference for the size class 2.0–3.0 mm in diameter, which is much smaller and lighter than the preference for the artificial seeds. The preference of seeds from different plants showed very big variability. There was no correlation between the preference and any of the following variables of the seeds: fresh mass, dry mass, water content, energy content, and nitrogen content. No evidence for energy optimizing in food selection in Messor capitatus was found.
The energetic reward of bringing any seed back to the nest will, under all normal conditions, be much higher than the energetic expenditure. For example, the energetic content in a wheat seed is about 650 Joule, which is sufficient energy for a worker ant of Messor capitatus to carry the seed for a distance of 6.5 km at a temperature of 30oC.
High—altitude Appennine grassland ant communities were studied by sampling two stations with very different exposures and plant associations. In spite of these differences, the distribution of the ant population is very similar in the two stations, and it is probable that the situation found on Monte Terminillo also exists on most of the high altitude grasslands of the central Appennines. Two species, Lasius alienus and Tetramorium caespitum, predominate; and a few others are quantitatively of lesser importance. The dominant species, which have similar alimentary regimes, and whose colonies are randomly distributed, forage at somewhat different hours.
The respiratory metabolism of workers of Messor capitatus (Latreille) was measured using standard micro‐Warburg techniques on single individuals. The experiments were carried out at 10, 20, 25, 30 and 40oC, and the respiratory quotient (RQ), measured for the same individuals at 30oC, was found to be 0.77. The specific respiratory rate (y, in μl O2/mg dry weight/h) could be described by the following equation: Iny = ‐2.24 + 0.098r ‐0.258 In W; where T is temperature and W is the dry weight in mg. The Q10 for M. capitatus in the temperature interval 20–30oC was 3.4, a higher value than for other ants.
The energy costs of movement and carrying were determined by using the RQ to convert the continuous measurement of CO2 produced at 30oC by Enfiuran anaesthetized workers (‘resting metabolism’), by running workers and by workers loaded with a 20 mg weight to units of energy. The resting metabolism was 10.0±1.0 mJ/mg fresh weight/h. The cost of running (Y in joule per km) could be described by: Y = 3.865 + 0.363 Wf, where Wf is fresh weight in mg. The cost of transport for all experiments could be expressed as 0.64 × the cost of running.
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