Shell shape affects movement patterns and microhabitat distribution in the hermit crabs Calcinus elegans, C. laevimanus and C. latens

This study examined the influence of shell shape on the distribution and movement patterns of three species of Hawaiian hermit crabs: Calcinus elegans, C. laevimanus, and C. latens. Field surveys showed strong differences in shell use depending on habitat. Individuals of C.elegans and C. latens were more frequently in unusual shapes of shells (the cowrie Cypraea caputserpentis and the variable worm shell Serpulorbis variabilis) when in tide pools and in more standard gastropod shells, such as the dog whelk Nassarius papillosus, when found in the subtidal. In addition, for both C.elegans and C. latens in tide pools, most crabs in unusual shaped shells were out on top of rocks, whereas most crabs in shells that were standard shapes were under rocks.In the laboratory, individuals of C.elegans and C. laevimanus in unusual shells initiated more shell exchanges and when given empty shells crabs readily occupied the standard shaped shells, but crabs did not move into the unusual shaped shells. Mark-recapture experiments in the field showed that C. elegans in standard shaped shells moved out of tide pools and stayed longer when placed on subtidal coral heads, whereas crabs in unusual shaped shells stayed in tide pools and did not stay on subtidal coral heads (in part due to predation). Laboratory tests showed that C. elegans in unusual shaped shells were more readily dislodged by surge than crabs in standard shaped shells. Thus, the difference in movement patterns in preferred vs. unpreferred shell shapes is an important factor influencing the microhabitat distribution of these hermit crabs.     

Resolving spatio-temporal uncertainty in rare resource acquisition: smell the shell

Complex environments present substantial spatio-temporal uncertainty in where and when rare ecological resources become available. How animals navigate this uncertainty to turn the seemingly unpredictable into the predictable is a fundamental question in evolutionary ecology. Here we use subtidal hermit crabs (Pagurus acadianus) as a model system to experimentally test in the field how animals resolve spatio-temporal uncertainty in resource availability. Quadrat sampling within the subtidal zone revealed that hermit crabs face an extreme ecological challenge, based on the rarity of empty shells across space and time. We show how this spatio-temporal uncertainty is ultimately resolved using long-distance chemical cues, which are associated with non-destructive shell predation on living gastropods, the original source of shells. By experimentally releasing cues that simulated the chemical by-products of predation, we reveal that certain flesh cues provide fine-grained information about the precise spatial and temporal window of new shell availability. These cues were most attractive to individuals with the greatest existing resource needs, and in the absence of this information individuals were highly constrained in their ability to discover newly available resources. Broadly, these experiments reveal that exploiting simple cues from heterospecific predators can provide a solution to the general ecological challenge of finding resources that are rare in space and time.     

Crab: snail size-structured interactions and salt marsh predation gradients

We studied size-structured predator-prey interactions between blue crabs (Callinectes sapidus) and marsh periwinkles (Littoraria irrorata) with a combination of field studies, laboratory experiments and individual-based modeling. Size distributions of Littoraria differed among years at the same sites in a salt marsh and could largely be explained by dominance of strong cohorts in the population. At a given site, abundance increased with elevation above tidal datum. Size-selective predation by blue crabs does not appear to be an important regulator of snail size distributions but may have a major effect on local abundance. Laboratory studies indicated that predator-prey interactions between Callinectes and Littoraria are strongly size-dependent. Crabs were generally effective at feeding on periwinkles at size ratios greater than approximately 6 (crab width: snail length). At lower size ratios crabs were far less effective at manipulating the snails, which often survived but with damaged shells. An individual-based model which incorporated information about incidence of snail shell scarring (resulting from non-lethal interactions) and snail density, predicted reduced predation rates and smaller average crab size with distance from the low tide refugium for crabs.     

An environmentally induced tidal periodicity of microgrowth increment formation in subtidal populations of the clam Ruditapes philippinarum

The periodicity of increment formation in the shell of the Manila clam Ruditapes philippinarum was investigated in the subtidal zone of the Auray River estuary (South Brittany, France). Calcein markings were performed at different periods between May and October 2007 using in situ benthic chambers tented by scuba divers. This study shows that shell microgrowth increments were well-defined and deposited with a tidal periodicity in the subtidal zone, providing the calendar base for high-resolution ecological studies and environmental reconstruction from these R. philippinarum shells. Endogenous rhythmicity in shell microgrowth increment formation and oxygen consumption was previously documented in this species from intertidal flats. Our study suggests that, in the subtidal zone, Manila clams' rhythmic activity may be controlled by such an endogenous process, synchronized by tidal cues. As in other bivalves, R. philippinarum is an osmoconformer euryhaline bivalve. The tidal rhythmicity of shell microgrowth increments in subtidal specimens of this species could be explained by a behavioral adaptation of valve closure at low tide to protect the clam from low salinities and/or to synchronize with food availability. Finally, large inter-individual variability in tidally associated growth rates and asynchronous growth breaks were observed, and could be due to genetic variability between individuals, asynchronous partial spawning events or predation.     

Why are intertidal snails rare in the subtidal? Predation, growth and the vertical distribution of Littorina littorea (L.) in the Gulf of Maine

The North Atlantic gastropod Littorina littorea exhibits a characteristic “intertidal” distribution: the snail is abundant in the littoral zone but scarce in the shallow subtidal and the relatively few subtidal individuals are larger (in shell size) on average than those in the intertidal zone. For highly mobile species like L. littorea, this vertical distribution is primarily determined by directional movement. Biotic and abiotic factors vary across tidal heights, and natural selection for movement to shore levels where fitness is maximized provides the ultimate (evolutionary) explanation for vertical distribution patterns. In this study, we asked whether variation in growth rate and/or predation pressure among tidal heights provide an ultimate explanation for vertical gradients in L. littorea size and abundance. We used a cage experiment to compare juvenile growth rate among tidal heights and a series of field and laboratory experiments to examine variation in predation pressure among tidal heights and snail size classes. Juvenile growth rates were highest in the low intertidal zone, declining at both higher and lower levels. Predation risk for tethered L. littorea increased with both decreasing tidal height and decreasing body size (shell height). Almost all tethered prey were consumed by shell- breaking predators and a census revealed that the two most abundant such predators were the crabs Carcinus maenas and Cancer borealis. Laboratory feeding experiments were used to compare size-dependent prey vulnerability and prey-size preferences for these two key predators. We found that L. littorea vulnerability decreased with increasing snail size and increased with increasing size of both predator species. However, whereas C. borealis were capable of consuming even the largest L. littorea, most Carcinus were unable to feed on individuals larger than 10 mm in shell height. Additionally, C. borealis preferred larger sizes of L. littorea than did Carcinus. Thus, Carcinus, which co-occurs with L. littorea in the intertidal, is a much less effective predator than C. borealis, which is found primarily in the subtidal. We conclude that predation on L. littorea by C. borealis and other subtidal consumers has resulted in the scarcity of this ecologically important grazer in the subtidal. This effect has been produced both through direct predation and by imposing strong selection for movement of L. littorea to higher tidal zones.     

Will providing a filamentous substratum in the water column and shell litter on the bottom increase settlement and post-larval survival of the scallop Argopecten purpuratus?

The marked variability in the natural recruitment of Argopecten purpuratus, a common characteristic for many marine invertebrates with a pelagic larval stages, with important consequences for community functioning, is a problem for the fishery on this species. We ran experiments in the subtidal zone in Tongoy Bay, Chile, to test whether providing a filamentous settlement substratum in the water column and shell litter on the bottom would increase the settlement and post-larval survival of scallops. We placed collectors made of Netlon® 50 cm above the sand and mud bottoms, and three and a half months later there were significantly more scallop spat on the bottom under the collectors (38.5 ind m^− 2), than in areas without collectors (0 ind m^− 2), or in controls where collectors were installed but a bag around the collector prevented the juveniles from falling to the bottom (4.8 ind m^− 2). Also, the addition of either entire or broken scallop shells to the bottom resulted in increased settlement of juveniles on the bottom (33.7 ind m^− 2 with entire shells and 48.1 ind m^− 2 with broken shells), compared to plots where no shell debris was added (0 ind m^− 2). The 2 week survival rate of juveniles (< 3 mm shell height) added to plots covered with entire scallop shells (12.4%) and to plots covered with broken shells (15.1%) was greater than in plots where we did not add shells (3.5%). These results suggest that substrate availability explains spatial variability of recruitment for this species, while temporal variability (between years) is mainly the consequence of larval supply. The manipulation of substrates can locally increase settlement, but will not remove the temporal variability. Whereas our experiments provide useful insights into strategies for managing or establishing local scallop populations, experiments over a longer term and at a large scale are needed to further understand the community functioning in order to develop a strategy for managing this fishery resource.     

Chaoborus and fish-mediated influences on Daphnia longispina population structure,dynamics and life history strategies

Summary This study examined the long term effects of predation by larvae of the midge Chaoborus and simulated fish predation on experimental Daphnia longispina populations. Chaoborus predation, relative to fish predation, led to populations composed of larger individuals as a whole, larger egg-bearing individuals, and a larger primiparous instar. Daphnia retained helmets beyond the first instar in response to the presence of Chaoborus. Both types of predation, relative to predator-free controls, reduced prey population size and rates of increase, but increased population death rates. The reduction in population size due to predation led to increased resource availability for individuals remaining in the populations and increased individual fecundity in the predation treatments. The differences noted between the Chaoborus, fish, and control treatments increased with predation intensity.     

Shell recruitment in the Mediterranean hermit crab Clibanarius erythropus

Gastropod shells are vital for the majority of hermit crab species, being essential for their survival, growth, protection, and reproduction. Given their importance, shells are acquired and transferred between crabs through several modalities. We conducted observations and experiments at the Asinara Island (Sardinia, Italy) to investigate the efficacy of the different behavioral tactics adopted by the hermit crab Clibanarius erythropus to acquire shells, such as: (1) locomotion and activity at different tidal phases; (2) attendance at shell-supplying sites (simulated predation sites with five different odors: live and dead gastropods, live and dead crabs, predator); and (3) interactions with conspecifics in aggregations on simulated gastropod predation sites. In each tidal phase, locomotion was slow (0.7 cm min^− 1) and, as a consequence, the probability of encountering empty shells and conspecifics was low. Simulated gastropod predation sites quickly attracted a larger number of hermit crabs than the other sites tested. Aggregations seemed to function as shell exchange markets, as previously suggested for other species: the first attendant took the experimental shell and a chain of shell exchanges among conspecifics followed. Our results show that, in C. erythropus, aggregation is the most efficient tactic for the acquisition of new shells, whereas in other species, such as Pagurus longicarpus, it is associated with exploitation ability due to the intense locomotion. The interspecific plasticity in hermit crabs' behavior is confirmed.     

Size-specific growth patterns and estimated longevity of the unionid mussel (<Emphasis Type="Italic">Pronodularia japanensis</Emphasis>)

Despite the dwindling populations and an urgent need for conservation of unionid freshwater mussels in Japan, there are gaps in our understating of their fundamental ecology. This study examined size-dependent annual growth rates, elucidated size-specific intra-annual growth patterns, and estimated age and longevity of P. japanensis individuals for two locally isolated populations in agricultural drainage channels. Annual growth rates of P. japanensis were strongly size-dependent, with growth rates being exponentially decelerated with increasing shell length. Irrespective of sizes, individuals ceased to grow in winter when water temperature fell below 10°C. Intra-annual growth patterns were weakly explained by the changes in water temperature and differed among size classes; juveniles (<25 mm) maximized growth rate in May whereas the growth rates were the highest in June or July for larger individuals. Only adult individuals exhibited growth cessation in the July–August period, suggesting that energy investment was directed towards reproductive activities. Adults also showed negative growth rates (shrinkage of individuals) in winter, suggesting possible dissolution of shell margins. Age estimation based on two 1-year periods suggests that large numbers of P. japanensis individuals were >10 years old, and the oldest individuals were >20 years old for both study populations. Our findings suggest that anthropogenic activities conducted in spring may have strong influences on juveniles and population dynamics of P. japanensis and underscore the need for accurately determining age and longevity of remaining populations of unionid mussels.     

Habitat-specific size structure variations in periwinkle populations (<Emphasis Type="Italic">Littorina littorea)</Emphasis> caused by biotic factors

Shell size distribution patterns of marine gastropod populations may vary considerably across different environments. We investigated the size and density structure of genetically continuous periwinkle populations (Littorina littorea) on an exposed rocky and a sheltered sedimentary environment on two nearby islands in the south-eastern North Sea (German Bight). On the sedimentary shore, periwinkle density (917 ± 722 individuals m⁻²) was about three times higher than on the rocky shore (296 ± 168 individuals m⁻²). Mean (9.8 ± 3.9 mm) and maximum (22 mm) shell size of L. littorea on the sedimentary shore were smaller than on the rocky shore (21.5 ± 4.2 and 32 mm, respectively), where only few small snails were found. Additionally, periwinkle shells were thicker and stronger on the rocky than on the sedimentary shore. To ascertain mechanisms responsible for differences in population structures, we examined periwinkles in both environments for growth rate, predation pressure, infection with a shell boring polychaete (Polydora ciliata) and parasitic infestation by trematodes. A crosswise transplantation experiment revealed better growth conditions on the sedimentary than on the rocky shore. However, crab abundance and prevalence of parasites and P. ciliata in adult snails were higher on the sedimentary shore. Previous investigations showed that crabs prefer large periwinkles infested with P. ciliata. Thus, we suggest that parasites and shell boring P. ciliata in conjunction with an increased crab predation pressure are responsible for low abundances of large periwinkles on the sedimentary shore while high wave exposure may explain low densities of juvenile L. littorea on the rocky shore. We conclude that biotic factors may strongly contribute to observed differences in size structure of the L. littorea populations studied on rocky and sedimentary shores.     

EVIDENCE FOR PREDATION AS A FACTOR IN DETERMINING SHELL COLOR FREQUENCIES IN A MANGROVE SNAIL LITTORINA SP. (PROSOBRANCHIA: LITTORINIDAE)

It was hypothesized that in Littorina populations living on Avicennia marina in Moreton Bay, Queensland, yellow shelled individuals are at a selective advantage over other shell colors and that this advantage is due to differential selection by predators. Yellow shelled individuals were more likely to be recaptured than others, indicating a higher survival rate of yellows. When predation was restricted on ten mangrove trees, the apparent advantage of yellow shells was removed. After 18 months, the relative frequency of yellow shelled individuals was significantly lower on experimental trees than on control trees. A combination of selection for crypsis and for the less common morph is suggested as the mechanism maintaining the high levels of variation in this species.     

Long‐term population dynamics of a coral reef gastropod and responses to disturbance

The age‐specific density of the red‐lipped stromb Strombus luhuanus (Mollusca: Gastropoda) was monitored over 13 years (1981–1993) at four locations on the intertidal reef flat at Heron Island, Great Barrier Reef. Densities were highly variable, but there were persistent, location‐specific differences in population density, age structure and adult body size, the latter indicating that the populations were not extensively linked by adult movement. There was relatively high recruitment at most locations in 1984, 1989 and 1993, each occurring approximately 2 years after El Niño/Southern Oscillation events, although recruit density during these years varied in both space and time. The studied strombs experienced three disturbance events: (i) experimental harvesting at two locations (1984–1985); (ii) siltation from a harbour dredging operation (1987–1988); and (iii) a severe cyclone (1992). Resilience to harvesting at a local scale (0.5–2 ha) was high: density had recovered within a year, due to immigration of adults and older juveniles. Strombus luhuanus responded much more strongly to broad‐scale changes to its environment than to localized harvesting. After dredging, there was a progressive density decline coupled with low recruitment at two locations, and a later decline at a third location, followed by a recruitment‐driven rebound after the cyclone. Generalized environmental effects of siltation and the cyclone were also reflected in substantial changes in algal cover. Long‐term variations in environmental conditions probably cause high temporal variation over large spatial scales through effects on the survival of larvae or recruits. Localized short‐term field monitoring of such species would give a misleading picture of key factors affecting population dynamics.     

Morphological and ecological shifts in a land snail caused by the impact of an introduced predator

Introduced predators have become major threats to native animal species in oceanic islands. A number of studies have shown that alien predators have caused serious extinctions of island endemics. However, little attention has been paid to the evolutionary impacts of alien predators on native species. The present study shows that predation by black rats, Rattus rattus, has resulted in ecological and morphological changes in the land snail Mandarina anijimana from the island of Anijima in the Ogasawara archipelago. The frequency of empty predated shells has increased over the past 17–19 years in southern areas of the island. The shells of these snails were found to be significantly higher, smaller and darker in the survey in 2006 than in the survey in 1987–1989 performed in central and southern parts of Anijima, where predation by Rattus was serious. M. anijimana were formerly restricted to shallow broad-leaved litter, whereas they are currently found in deep palm litter, where predation pressure from Rattus may be lower. This suggests that increased predation pressure by Rattus has changed the habitat use of M. anijimana. The close association between shell morphology and habitat use of Mandarina species suggests that the habitat shift induced by the predation of Rattus has caused these changes in the shell morphology of M. anijimana over a period of 17–19 years.     

KIN INTERACTIONS IN A COLONIAL HYDROZOAN (HYDRACTINIA SYMBIOLONGICARPUS): POPULATION STRUCTURE ON A MOBILE LANDSCAPE

Many sessile colonial organisms intensively compete with conspecifics for growing space. This competition can result in either cooperative fusion or aggressive rejection between colonies, and some species have evolved highly polymorphic genetic systems that mediate the outcome of these interactions. Here we demonstrate the potential for interactions among close kin as the basis for the evolutionary maintenance of a genetically polymorphic allorecognition system in the colonial hydroid Hydractinia symbiolongicarpus, which lives on gastropod shells occupied by hermit crabs. Fusion between hydroids in the laboratory is restricted mainly to encounters between full siblings, whereas other encounters result in aggressive rejection. Natural selection acting on the costs or benefits of fusion between colonies could be responsible for the present maintenance of such a highly specific behavioral response, but only if encounters between fusible colonies still occur in contemporary populations. The large size of these hydroid populations and the mobility of the crabs should limit the potential for interactions among closely related hydroids on the same shell. However, RAPD polymorphisms among a large sample of hydroids from a population off the coast of Massachusetts indicate that genetically similar colonies are often found together on the same shell. Some genetic distances between colonies on the same shell were low relative to genetic distances between colonies on different shells or genetic distances between known full siblings from laboratory matings. We conservatively estimate that 2–18% of co-occurring colonies may be full sibling pairs. These observations suggest that encounters between genetically similar hydroids are common, despite the mobile nature of their habitat, and these encounters may provide frequent opportunities for natural selection to influence the evolution of cooperative and agonistic behaviors and their polymorphic genetic basis.     

Some Aspects of Hole-Boring Predation by Octopus vulgaris

Octopus vulgaris prey upon many gastropod species by boringholes in the shell, weakening the prey with a venom, removingthe entire prey, and eating it. When offered Strombus raninusthe Octopus quickly grasped the conch with one or a few arms,checked for occupancy by inserting an arm tip into the aperture,and passed the shell under the web to the mouth. The shell washeld against the buccal mass by the circumoral suckers and raspedrepeatedly with the radula, repositioned, and rasped again.There were brief pauses of apparent inactivity between the periodsof active rasping. The shell was penetrated at an approximatemaximal rate of 1.25 mm per hour. The boreholes averaged 0.93mm in outer diameter, 0.47 mm in inner diameter and 0.88 mmin depth. The boreholes were extremely variable in shape, size,and position on the spire. There was a marked preference forindividual animals to bore in a particular sector of the spire.Apparently the animals orient the shells by using the lip asa point of reference because lipless shells had the boreholesrandomly distributed around the shell.     

A biomechanical hypothesis explaining upstream movements by the freshwater snail Elimia

1. Many taxa of freshwater invertebrates show active upstream movements, particularly the snails. Hypotheses explaining this behaviour invoke the search for food or space, compensation for drift, avoidance of predation and hydrodynamic effects. The pervasiveness of upstream movements among remote lineages of snails (two subclasses, three orders, 10 families), however, suggests that snails may move upstream for mechanical rather than adaptive reasons.
2. It is proposed that upstream movements by snails are a function of torque on the snail's foot generated by hydrodynamic drag on the shell. When subject to high broadside drag-forces on their shells, snails are able to reduce torque and stabilize orientation only by directing their anterior aspect upstream.
3. Movements of the freshwater pleurocerid snail Elimia were studied by following marked free-ranging individuals in six streams in Alabama, USA (four species, eight populations).
4. Populations showed either no net movement (two streams) or significant upstream movements ranging to a mean of ≈40 m over a 3-month period (four streams). Movement patterns were stream specific rather than species or population specific. Within populations showing significant upstream movements, snails with shell lengths ≤10 mm showed little net movement. Larger snails showed movements from 0 to >200 m upstream.
5. A torque-constrained random walk model was used to perform a post hoc test of the hypothesis that upstream movements were a function of torque on the snail's foot generated by hydrodynamic drag on the shell. The model predicted upstream and size-dependent movement patterns that approximated those observed for snails in the field.     

Guppy populations differ in cannibalistic degree and adaptation to structural environments

There is considerable variation in cannibalism between different species and also between individuals of different species, although relatively little is known about what creates this variation. We investigated the degree of cannibalism in guppy (Poecilia reticulata) populations originating from high and low predation environments in Trinidad, and also how cannibalism was affected by the presence of refuges. Females from two populations were allowed to feed on juveniles from two populations in aquaria trials. The cannibalism was size-dependent and varied depending on both juvenile and female origin. Low predation females were more efficient cannibals and low predation juveniles were better at avoiding cannibalism compared to high predation guppies when no refuges were present. The high predation females were superior cannibals and the high predation juveniles were better at escaping cannibalism than the low predation guppies when refuges were present. We discuss whether the differences in cannibalism and response to refuge addition relate to predation-induced habitat shifts and differences in the guppies’ natural environment.     

Size and age composition of populations and growth of Mytilus trossulus (Bivalvia: Mytilidae) in the subtidal area of western Kamchatka

Fairly large Mytilus trossulus beds were found in the subtidal zone at depths to 40 m off the western coast of Kamchatka. The size and age composition of local populations and growth rates of M. trossulus in this region and at Atlasova Island were studied. Significant variability of the shell shape of mollusks was found. In the western Kamchatka subtidal, M. trossulus grew faster than in the northern Kuril Islands and eastern Kamchatka. Mussels attained commercial size (50 mm in shell length) in the fourth year of life in the former case and in the fifth-sixth year in other cases. Mollusks of different ages, from 1 to 8–9 year olds, were present in western Kamchatka populations; i.e., juvenile recruitment takes place regularly, while growth rates vary. Growth and population structure of M. trossulus are discussed in relation to the habitat conditions on the western Kamchatka shelf.     

The shell of <Emphasis Type="Italic">Hexaplex (Trunculariopsis) trunculus</Emphasis> (Gastropoda: Muricidae) as a mobile hard substratum for epibiotic polychaetes (Annelida: Polychaeta) in the Ria Formosa (Algarve coast—southern Portugal)

This work reports and illustrates secondary colonisation of Hexaplex (Trunculariopsis) trunculus shells by polychaetes in the Ria Formosa lagoon (Algarve coast—southern Portugal). Information is presented in terms of qualitative and quantitative data on epibiotic polychaetes, fouling frequency, degree of epibiosis, preferential areas for colonisation and incidence of shell damages. A total of 2,880 polychaetes belonging to 10 families were identified. Besides Spirorbidae (not quantified), the most abundant families were Serpulidae (67.5%), Sabellidae (10.2%), Sabellariidae (9.6%) and Cirratulidae (8.5%). From a total of 2,264 T. trunculus individuals analysed for epibiosis, 28.4% were non-fouled, 66.8% were intermediately fouled and 4.8% were heavily fouled. The fouling frequency, degree of epibiosis and incidence of damages in the shell spire increased markedly with T. trunculus shell length. Some epibiotic polychaetes were located preferentially on/or nearby particular features of T. trunculus shells, which probably facilitate settlement and tube construction, in addition to provide some protection against tube damage. The main consequences of epibiosis (benefits and disadvantages) for the gastropod basibiont (T. trunculus) are discussed. The present study apparently indicates that besides burrowing into soft bottom substrates, sporadic inter-tidal exposure and mutual predation on epibiosis, T. trunculus lacks other typical antifouling defence adaptations. Handling editor: K. Martens     

Differences in predatory pressure on terrestrial snails by birds and mammals

The evolution of shell polymorphism in terrestrial snails is a classic textbook example of the effect of natural selection in which avian and mammalian predation represents an important selective force on gene frequency. However, many questions about predation remain unclear, especially in the case of mammals. We collected 2000 specimens from eight terrestrial gastropod species to investigate the predation pressure exerted by birds and mice on snails. We found evidence of avian and mammalian predation in 26.5% and 36.8% of the shells. Both birds and mammals were selective with respect to snail species, size and morphs. Birds preferred the brown-lipped banded snail Cepaea nemoralis (L.) and mice preferred the burgundy snail Helix pomatia L. Mice avoided pink mid-banded C. nemoralis and preferred brown mid-banded morphs, which were neglected by birds. In contrast to mice, birds chose larger individuals. Significant differences in their predatory pressure can influence the evolution and maintenance of shell size and polymorphism of shell colouration in snails.