Ecology 6th Edition by Charles Krebs

Exercise 8

The British barnacle Elminius modestus extends higher on the shore in the intertidal zone than does the barnacle Semibalanus balanoides when the two species occur together. However, these two species have similar tolerances to desiccation, salinity, and temperature. The range of initial settlement of young barnacles is the same for the two species. Given these facts, can you suggest an explanation for the observation that E. modestus extends higher on the shore than S. balanoides?