Measuring feeding traits of a range of litter-consuming terrestrial snails: leaf litter consumption, faeces production and scaling with body size.

Plant litter decomposition is an essential ecosystem function that contributes to energy and nutrient cycling above- and belowground. Terrestrial gastropods can affect this process in various ways: they consume and fragment leaf litter and create suitable habitats for microorganisms through the production of faeces and mucus. We assessed the contributions of ten litter-feeding terrestrial snail species to leaf litter mass loss and checked whether consumption rate and faeces production scale with body size (i.e. shell size and shape), which may indicate that morphological traits can serve as proxies for consumption rate. Additionally, we compared the consumption rates of a subset of these species among litter types of two plant species which differ in resource quality (Fraxinus excelsior and Betula pendula). These snail species differed in their litter consumption rates. Consumption rates differed between the two litter types, whereas the rank order of litter consumption by the different species was independent of litter quality. Consumption rate and faeces production were positively related to shell size, whereas relative consumption rate and faeces production were related to shell shape, with more elongated snail species having lower relative consumption rates and faeces production rates. Our results show that easily measurable morphological traits scale with the feeding traits of snails, and represent useful proxies for consumption rate and faeces production, which are laborious to measure. Thus, estimated potential total consumption rates of snail communities along environmental gradients may be inferred from shell-size distributions. Our study contributes to a systematic trait-based evaluation of the importance of gastropods to litter decomposition.