Quantifying individual feeding variability: implications for mollusc feeding experiments

1. In order to quantify the level of variability in seedling consumption displayed by individual molluscs, we placed one snail ( Helix aspersa ) in each of 51 trays containing (7-day-old) Taraxacum officinale seedlings for 7 days. 2. Initially, individual snails displayed considerable variability in their consumption of seedlings; however, this variability declined with time. The consumption of seedlings was not related to individual snail mass. 3. A second grazing experiment, using five different snail densities in similar experi- mental conditions to the first, showed that increasing snail number reduced variability within treatment groups. 4. A computer simulation, based on data from the first experiment correctly predicted the basic form of the decline in feeding variability with increasing snail density found in the second. Post hoc changes to the model, based on empirical analysis of the second experiment to account for mutual interference, reduced discrepancies between empirical and model results. 5. This study highlights the consequences that individual feeding behaviour has on feeding trials with molluscs, and provides a simple method by which this variability can be quantified and accommodated within experimental design