Environmental conditions and seed traits affect seed dispersal patterns in a slug-legume model system

The outcome of seed fate (probability of predation or dispersal) depends on the interplay between granivores and seed traits. Furthermore, changing environmental conditions affecting granivore behavior might additionally alter seed dispersal patterns. Based on microcosm experiments and time-lapse videos, we tested in a structural equation model how dry or wet conditions in a slug-legume seed system affect slug movement behavior, thus influencing seed encounter, ingestion and dispersal locations. We additionally analyzed how interactions between slug weight, chemical and morphological seed traits determine the fate of ingested seeds and used point pattern analysis of seed locations to detect potential dispersal patterns. While dry or wet conditions had no direct effect on the time slugs spent moving, dry conditions significantly increased the slug's homing behavior. Higher slug movement increased the chance of seed encounter, smaller seeds with low seed coat permeability were preferably ingested and the proportion of ingested seeds increased with increasing seed oil content. A high proportion of ingested seeds was dispersed via endozoochory, but none of the tested seed traits could explain seed fate. Endozoochory led to clumped dispersal patterns around the slug's shelter with clustering significantly more pronounced for seeds in dry conditions due to increased homing behavior in slugs. These dispersal patterns indicate potential directed dispersal to moist microsites but whether this leads to higher recruitment and hence successful directed dispersal remains to be tested.