The seed bank in soil from the nests of grassland ants in a unique limestone grassland community in Ireland

Abstract

The seed content of nest soil of four species of ants Myrmica sabuleti, Lasius flavus, L. niger and Formica lemani was investigated in the semi-natural limestone grassland of the Burren, western Ireland. On-nest and off-nest soil samples were compared to determine whether ants promote plant species richness. Samples were collected, monthly, from May to September 2006 from the top 50mm of soil from 10 nests of each species, and from adjacent off-nest grassland soil (total 400 samples). After collection a total of 42 seed species were germinated and identified. L. flavus (both on-nest and off-nest samples) had the highest seed species richness of which 10 species had a high seedling representation (% affinity) for the nest of this species. Persicaria maculosa and Viola tricolour had a high percent affinity for the nests of L. niger, and these were significantly higher on the nest compared to the off-nest samples. Anagallis arvensis and Cerastium holosteoides also had significantly higher percent affinity for the nests of F. lemani. No species was associated with M. sabuleti. The high richness of seedling species associated with Lasius nests may be due to the specialised vegetation on the nest or ant activity. Since L. niger, F. lemani and M. sabuleti nest under stones it is likely that the seeds may be collected by ant activity. Although previously reported for L. flavus, the unique seed banks of the ant nests can account for localised mosaic patches of different vegetation.