Role of biological habitat amelioration in altering the relative responses of congeneric species to climate change

The distribution of most species is expected to alter in response to climate change. Pre- dictions for the extent of these range shifts are frequently based on 'climate envelope' approaches, which often oversimplify species responses because many do not consider interactions between physical and biological factors. The local persistence of some species, however, is likely to be strongly modulated by microhabitat-forming organisms. Using congeneric patellid gastropods with northern/ boreal and southern/lusitanian distributions, we have demonstrated how the loss of habitat-forming macroalgal species could modify species responses to climate change. The northern limpet Patella vulgata preferentially aggregates beneath Fucus spp. When Fucus vesiculosus was experimentally removed, to simulate a decline in macroalgal abundance in response to climatic warming, P. vulgata suffered increased mortality or relocated home scars, often to nearby Fucus spp. patches. In contrast, the southern limpet P. depressa did not aggregate beneath Fucus spp. and showed no response in terms of movement or mortality to the loss of F. vesiculosus. Based on these results, we predict that the loss of Fucus spp. will influence the relative abundance of these 2 limpet species, particularly at the distributional limit of Fucus spp. In addition, differences in the aggregative behaviour of these limpet species will result in changes in the spatial distribution of grazing in the intertidal, with likely consequences for community dynamics. These outcomes could not be anticipated from predictions based on direct responses to temperature alone, highlighting the need for biotic and abiotic factors to be incorporated into predictions of species responses to climate change.