Edinburgh Napier University

  A key prediction to emerge from community assembly models is that resistance to invasion increases as the community matures. Three epifaunal communities of differing age were developed upon artificial substrata in the Firth of Forth, Scotland, to examine whether community age influenced the rate of establishment of new recruits. Four repeat experiments assessed the numbers of species and individuals invading a controlled amount of free space in these communities. The oldest communities were invaded by the smallest mean number of species in each experiment although these differences Were significant for only 1 experiment. Multiple regression showed that age was the most significant predictor variable of the percentage coverage of new species. Because there were no significant effects on communities only a few centimetres away, the mechanisms by which community age controlled invasion in these experiments operate over small spatial scales. These data support the prediction that older communities are more resistant to invasion, but only if the term invasion includes further recruitment of species already present in the community. However, the experimental design does not distinguish between the effects of age per se, and those of different assemblage sequences. As expected, species responded in different ways to community age, and species composition played an important role in determining the success of invasion.