Comparisons (mean ± 1 SE) between <i>Littorina littorea</i> (white bars) and <i>Gibbula umbilicalis</i> (black bars) from trials with conspecific and heterospecific pairs.

<p>The values are means, standardized with respect to the control, for each species. Negative values indicate a reduction relative to the control while positive values indicate an increase relative to the control. A) the number of scans in which each individual was recorded out of the water in predator avoidance (GLM repeated measures: within factors Trial*Treatment, F_2,27 = 4.141, p<0.03; between factors Treatment F_2,27 = 3.35, p<0.05); B) the number of scans in which each individual was recorded eating <i>Ulva</i> (GLM repeated measures: within factors Trial*Treatment, F_2,27 = 24.918, p<0.0001; between factors Treatment F_2,27 = 6.055, p<0.007); and C) the amount of <i>Ulva</i> eaten at the end of the trial (K-Ω <i>χ</i>²₂ = 8.476, p<0.015). Bars in C are shown in grey as it was not possible to determine the amount of <i>Ulva</i> eaten by each individual.