Specific damage recognised on land snail shells as a tool for studying predation intensity: differences related to habitat and predator types

Abstract

Shell formation is the main defensive strategy against predation for the majority of snails. Therefore, various predators have had to develop a variety of techniques how to overcome this barrier. As shells can persist in a calcium-rich environment for a long time, specific external or internal traces on shells left by predators indicate whether and who killed the snail. Based on litter samples collected at 30 sites of five different habitat types, the intensity and type of predation were assessed. The minimal predation rate varied between 0.0 and 21%, with an average of 8%. The highest rate was observed at limestone steppes, on average 15%. Beetles were found to be the most common predators of snails; however, predation by snails was more common in calcareous fens. Predation by some vertebrates and dipteran flies was also recognised. To test the role of mouth barriers as a means to reduce predation by carabid beetles that break the shell from an aperture, we analysed the predation rate separately on adult and juvenile shells using 24 populations of the steppe snail Granaria frumentum (Draparnaud, 1801). As expected, carabid beetles chiefly preferred juveniles compared to adult shells (Wilcoxon test, p < 0.001). On the contrary, the parasitoid fly Pherbellia limbata (Meigen, 1830) and Drilus beetles preferred adults. We found that predation by carabid beetles positively increased with prey abundance (R2 = 42.8%, p = 0.021), while no relation was observed for the parasitoid (p = 0.703), likely due to their feeding specialisation.

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

“…In addition to SIA, we also performed an analysis of specific external or internal traces recognized on land snail shells, that is, the analysis of fresh empty shells, according to Němec & Horsák (2019). With this approach, we can identify and also quantify foraging activity of various malacophagous predators using empty shells of their victims (Němec & Horsák, 2019).…”

“…In addition to SIA, we also performed an analysis of specific external or internal traces recognized on land snail shells, that is, the analysis of fresh empty shells, according to Němec & Horsák (2019). With this approach, we can identify and also quantify foraging activity of various malacophagous predators using empty shells of their victims (Němec & Horsák, 2019). These traces include also damages made by carnivorous gastropods, being represented by a specifically rasped hole in the shell wall (Millar & Waite, 2004; Myzyk, 2014; Němec & Horsák, 2019).…”

Shell morphology, growth pattern and population dynamics of the land snail Xerolenta obvia (Menke, 1828) in two areas of different climatic conditions within a temperate climate region

“…Selection for crypsis and the tendency for different morphs to select appropriate microhabitats may all have effects (Jones et al 1974, Allen & Weale 2005, Holmes et al 2017, Rosin et al 2018. With only two populations available, we cannot comment further other than to note that X. obvia and other species of open, lime-rich sites such as Granaria frumentum may be subject to heavy predation (Němec & Horsák 2019), and that genetic drift and founder effects may be significant in small, isolated populations (Jones et al 1977, Cook 1998, Ożgo 2008. Such isolation is typical for X. obvia populations in Poland (Wiktor 2004).…”

Morphometric traits of shells determine external attack and internal utilization marks in the Roman snail in eastern Germany

“…The present study documents a high potential predation pressure and a positive relationship between external attack and internal utilization marks in subpopulations of H. pomatia in unfavourable environmental conditions. Previous studies documented that protection of H. pomatia subpopulations against vertebrate predators can contribute to an increase of population sizes (Sherley et al, 1998;Neuweger et al, 2001). In such conservation programmes, it is important to consider that external predators prefer larger individuals.…”

“…Natural enemies of terrestrial snails often leave marks on the shell, either through external attack marks damaging the shell or internal utilization marks by larvae of pupae. Only two previous studies have used these marks to contribute to a better understanding of predation on terrestrial snails: Millar and Waite (2004) recorded patterns of shell damage in an English woodland and Němec and Horsák (2019) recently compared the identity of predator groups causing marks on the shells of the steppe snail Granaria frumentum (Draparnaud, 1801). Predation at the population level affects morphometric traits of shells (e.g.…”