Abstract
Based on the heterogenous nature of Lipophrys pholis diet, the stage of the species’ ontogenetic development when major niche shifts occurred was identified, and the causes that force this blennid to change its feeding behaviour, vertical distribution and shelter occupation were considered. The diet analysis of the different size classes consistently showed two clusters, grouping individuals 8 cm total length. This shift occurred simultaneously with the onset of reproduction; it seemed to be independent of inter‐ and intraspecific competition and reflected a quantitative and qualitative alteration of the dietary constituents. The analysis of the diet of other sympatric intertidal blennids, Lipophrys trigloides and Coryphoblennius galerita , showed that, apart from the first developmental stages, there seemed to be no important dietary overlap. The inevitability of this niche alteration could be explained by the combination of at least two different factors: the development of the scraping capability that enabled the fish to feed on large benthic prey, together with the limited number of suitable shelters that were available in rock pools.