Effects of redispersal of seeds by ants on the vegetation pattern in a deciduous forest: A case study

The Aoristic composition and distribution of mature plants, seedlings, and soil-seed material in both ant territories and territory borders between co lonies of two ant species, Lasius fuliginosus and Formica polyctena, were c ompared in a deciduous forest in central Ukraine. Additional seed samples w ere taken from ant nests. Workers of both species collect seeds of myrmecoc hores, but only individuals of F. polyctena relocate seeds to territory bor ders after the removal of elaiosomes. Borders of F. polyctena territories a re thus 'garbage dumps' of waste organic material and probably also nutrien t-enriched microsites. The floristic composition of L. fuliginosus' territo ry differed from that of the territory borders and F. polyctena territory o wing to a lower abundance of myrmecochores in the former. There were no gre at differences in the abundance or in the number of species (altogether fou rteen species) in mature myrmecochores or non-myrmecochores among the sampl ing sites. However, the abundance and to some extent the number of species (altogether 21 species) of seedlings of myrmecochores (but not of non-myrme cochores) were lower in L. fuliginosus territory than in the other sampling sites. In particular, seedlings of two large-seeded myrmecochores, Asarum europaeum and Viola odorata, were more abundant in territory borders than i n the territories. With a small-seeded myrmecochore, Ballota nigra, no such differences were found. Seeds of large-seeded myrmecochores, small-seeded myrmecochores and non-myrmecochores were more abundant than expected in the territory borders, in the nest of L. fuliginosus, in the nest of F. polyct ena, respectively. It is suggested that seed how from F. polyctena nests to the territory borders results in an increase in the seed-dispersal distanc es from the parent plant and among seeds dispersed in both small- and large -seeded myrmecochores. In large-seeded myrmecochores, this also results in a higher likelihood of reaching 'garbage dumps'. The influence of ant behav iour on plant seed flow with different seed-dispersal strategies are discus sed. (C) 2000 Editions scientifiques et medicales Elsevier SAS.