Stable isotope analysis suggests low trophic niche partitioning among co-occurring land snail species in a floodplain forest

Land snails are abundant invertebrates in many terrestrial ecosystems, playing an essential role in food webs and nutrient cycling. Although snails are commonly considered general grazers with a strong tendency to omnivory, their foraging strategy is well documented only for a few species. Virtually no data exist on trophic niche partitioning within snail assemblages. To fill this gap, we analyzed naturally occurring stable isotope (delta C-13, delta N-15), an approach widely applied in ecological research, but only rarely in terrestrial snail studies. We collected ten individuals of the dominant co-occurring land snails (i.e., Aegopinella nitidula, Fruticicola fruticum, Oxyloma elegans, Succinea putris, Trochulus villosulus and Zonitoides nitidus) in a floodplain forest floor, along with their potential food sources and other invertebrates. All species, except for A. nitidula, showed high intraspecific variation in isotope signatures, indicating their opportunistic feeding behavior. Such a high intraspecific variation combined with the active movement range of all the species allows switching between food sources based on their accessibility. We observed that the trophic niches of the studied species highly overlapped, except for Z. nitidus. This suggests that trophic niche compartmentalization among co-occurring species does not seem to be the mechanism to avoid competition for food. Virtually unlimited resources for snail food are assumed to explain the coexistence of many species in high-density populations. Our results add to this concept of assembly rules in snail species by the finding of highly variable and overlapping trophic niches among the majority of the studied species.

Automated summary

This study analyzed stable isotopes of various land snails and found high intraspecific variation in feeding behavior among all but one species, indicating opportunistic feeding. The trophic niches of the studied species highly overlapped, suggesting that competition for food may not be avoided through trophic niche compartmentalization. This highlights the potential for coexistence of multiple snail species in high-density populations due to virtually unlimited food resources.