The production ecology of the monogynous ant Lasius niger was investigated for 3 populations in dune valleys of different age. Colony density, worker headwidth and production of sexuals were maximal in immature dune grasslands, at levels just above the dune slack vegetation. Worker headwidth and queen production were reduced by the presence of Lasius flavus but male production was unaffected. Correlations between the production of sexuals and nearest neighbour distance or worker number per colony also appeared to be dependent on the presence of L. flavus. Population means of queen investment frequencies per colony were 0.75 and 0.50 in the absence and presence of a dense L. flavus population, which equals investment ratios of 3:1 and 1:1, respectively. -from Authors