• alga;
  • amphipod;
  • dispersal;
  • herbivory;
  • host choice

Abstract  The spatial arrangement of plants may constrain the expression of herbivore preferences due to interaction between the scales of herbivore mobility and vegetation structure. I tested the hypothesis that the presence of the herbivorous marine amphipod Peramphithoe parmerong (Ampithoidae) on a low-preference, poor-quality host (the brown alga Padina crassa) was due to limited dispersal and the clumped nature of algal distributions. In contrast to limited dispersal in laboratory assays, amphipods rapidly colonized vacant algae in the field with natural densities being achieved within 1 day. These high rates of colonization did not decline with increasing distance from existing algal beds over the spatial scales separating Pa. crassa from the higher-quality host algae (Sargassum spp.). Thus, the spatial arrangement of host algae did not interact with herbivore mobility to constrain host choices.