Moss Capsules as Food of the Harvester Ant, Messor

Abstract

Harvester ants, Messor spp., were observed feeding on moss capsules in a winter when no other food sources were available. The ants climbed up the seta, gnawed off the capsules and carried them to their nests. In the semiarid region where this phenomenon was observed, suitable climatic conditions for spore maturation are rare, and feeding of ants on moss sporophytes even more strongly reduces reproduction by spores. An ecological study carried out during the years 1977-80 included observations on the harvester ant (Messor spp.) as a seed collector. The locality for research was in the Northern Negev of Israel (20 km NW of Beer-Sheva), in a plain covered by loess, elevation 100 m a.s.l. with average annual rainfall of 250 mm. It is a semiarid annual grassland densely covered by mosses during the early winter. The mosses revive and their spores germinate following the first rain (which may occur between October and January), and they dry out with the desiccation of the upper soil layer. Periods between rains are usually too long to enable mosses to complete their life cycle and produce sporophytes before drying out. Winter of 1979-80 was exceptional in its prolonged and densely spaced rains. Conditions resulting from this were highly favourable for mosses, and sporophytes were formed abundantly. By the end of January and the beginning of February, mosses on the loess plain were bearing mature sporophytes, while phanerogams were still at their vegetative growing stage. The dense tufts of sporophytes that appeared simultaneously made them suitable for predators at a time when no seeds were available. The widespread mosses on the loess plain are Aloina aloides var. ambigua (Bruch & Schimp.) Craig, Crossidium crassinerve De Not., to a lesser extent Bryum bicolor Dicks., and some others. The majority of sporophytes of Aloina mature about two weeks before those of Crossidium (mid-January, instead of the beginning of February). Capsules of both species are borne on a straight seta (the setae of Aloina are longer and have larger capsules than those of Crossidium); in Bryum the seta is inclined. HARVESTING Observed for Aloina aloides, January 15, 1980. Harvesting ants (Messor ebeninus and a few colonies of M. semirufus) climb up the seta, check the capsules with their mandibles (possibly to judge size), turn their body downward and gnaw through the seta at the base of the capsule (Fig. 1, then both fall to the ground. The capsules are then carried to the nests. Observed for Crossidium crassinerve, February 1, 1980. In the meantime, all Aloina sporophytes had been harvested. The ants were found to be active in nearby patches of Crossidium. They climbed up the seta (shorter in this species) but did not turn around before cutting the capsules. Some large ants harvested the capsules while remaining on the ground. In Bryum bicolor, which is sparsely distributed, the inclined capsules were cut off by the ant in the two ways mentioned above, depending on the size of the ant and the sporophytes (Fig. 2). TRANSPORT Observed February 1, 1980. Ants transporting Crossidium sporophytes were seen to form a line, which in one case reached 15 m in length. The average pace of transport of capsules into the nest 007-2745/80/524-525$0.45/0 This content downloaded from 157.55.39.105 on Fri, 07 Oct 2016 04:53:56 UTC All use subject to http://about.jstor.org/terms 1980] LORIA & HERRNSTADT: MOSS CAPSULES 525 ~` 'C ~L ?__ -' ? ~`?t. r; i'~ ~R ?