Mortality, behavior and the effects of predators on the intertidal distribution of littorinid gastropods.

Predators can affect the vertical distribution of mobile intertidal invertebrates in two ways: they can (1) cause greater mortality of prey at certain intertidal levels, and (2) induce prey to seek safer intertidal areas. In this study, we investigate whether low-intertidal and subtidal predators affect the intertidal distribution of two congeneric species of small herbivorous gastropods of northeastern Pacific shores, Littorina sitkana Philippi 1846, and L. scutulata Gould 1849. In particular, we tested the hypothesis that predators affect the distribution of these snails by inducing them to seek higher and safer intertidal areas. On a wave-sheltered shore in Barkley Sound, British Columbia, L. sitkana and L. scutulata were both killed by predatory crabs (e.g., Cancer productus) more frequently when tethered near the lower limit of their intertidal distribution ( approximately 1 m) than when tethered where they were most common ( approximately 2.5 m), suggesting that high mortality rates are partly responsible for the lower-limit of these snails' intertidal distribution. However, two field mark-recapture experiments indicated that the snails' behavioral response to predation risk also influences their distribution. In the first experiment, snails from the 2.5-m level (low risk) transplanted to the 1.0-m level (high risk) displayed a strong and consistent tendency to move shoreward, especially L. sitkana, some traveling 10-15 m in 2-3 days to regain their original level. These shoreward movements were especially precise in the northern part of the study area, where predation rates on tethered snails were greatest. Furthermore, larger more vulnerable snails were more strongly oriented shoreward than smaller individuals, indicating that antipredator behavior might also contribute to intertidal size gradients in these species. In the second mark-recapture experiment, we manipulated predation risk using small cages and found that snails exposed to the odors of C. productus crabs foraging on conspecific and heterospecific snails displayed more precise (L. sitkana and L. scutulata) and longer (L. sitkana) shoreward movements than snails held in control conditions. These results provide the first experimental evidence that antipredator behavior may contribute to the intertidal distribution patterns of littorinids.

Interpopulation and context-related differences in responses of a marine gastropod to predation risk.

We conducted laboratory experiments to investigate interpopulation differences in the behavioural responses of the whelk Buccinum undatum to the predatory lobster Homarus americanus and the asteroid Leptasterias polaris, both in the absence and presence of feeding opportunities. Whelks from three populations in the eastern North Atlantic (1) responded to lobsters by displaying avoidance behaviours (burrowing in the sediments or retreating inside their shell), (2) responded to asteroids by displaying escape responses (rapid crawling, shell rocking behaviour or foot contortions), and (3) more often refrained from feeding in the presence of a lobster than in the presence of an asteroid. Although whelks from the three populations responded similarly to lobsters and asteroids, interpopulation differences were evident. Thus, whelks from populations sympatric with a given predator more frequently displayed 'appropriate' antipredator behaviours (i.e. avoidance in the presence of a lobster, and escape in the presence of an asteroid) than did whelks allopatric with that predator. Also, whelks from a population sympatric with both predators fed less readily in the presence of a given predator than did whelks allopatric with that predator. However, the presence of a lobster or an asteroid had the same impact on the feeding response of whelks from two populations with contrasting predator fields, one sympatric with lobsters, but allopatric with asteroids, and one sympatric with asteroids, but allopatric with lobsters. The results of our study indicate that coexistence (over evolutionary or ecological time) with lobsters and asteroids increases the propensity of the whelk to display avoidance and escape behaviours in the presence of lobsters and asteroids, respectively, but has a less predictable effect on how whelks trade off predation risk and food acquisition. Studies are needed to investigate the roles of inheritance and experience on the development of antipredator behaviours and decision making by prey animals when predation risk conflicts with other fitness-related activities such as the acquisition of food or reproductive opportunities. Copyright 1999 The Association for the Study of Animal Behaviour.

A field test of threat sensitivity in a marine gastropod

In the Mingan Islands, the whelk Buccinum undatum displays defensive manoeuvres to both contact and water-borne chemical cues from the predatory asteroid Leptasterias polarisIn spite of this, whelks occasionally aggregate in great numbers near L. polaris while it is ingesting a prey; they then attempt to steal food from their predator and also wait for leftovers. In this study, the response of whelks in different types of encounters with L. polaris was examined to test the hypothesis that whelks are sensitive to the magnitude of the threat their predator represents. In a field experiment, whelks consistently fled both non-feeding and feeding L. polaris (asteroids used were consuming small prey items that were unlikely to provide food for whelks). When current flow was stable, whelks fled more directly down current and more frequently displayed violent defensive behaviours, in response to non-feeding L. polariswhich presented a higher risk, than in response to feeding asteroids (lower risk; 47% versus 2%). Consequently, whelks tested with non-feeding asteroids more rapidly distanced themselves from the predators than did whelks tested with feeding asteroids. In a field survey, there were more active whelks in the vicinity of cruising (higher risk) than stationary (lower risk) L. polaris (53% versus 14%). Among those whelks that were active, defensive behaviour patterns such as shell rocking and leaping escape movements were frequently shown by whelks near cruising predators (69%), but never by whelks near stationary predators (0%). The discriminative capabilities apparent in these results are likely to be adaptive, because they enable whelks to limit the cost of escape responses while still keeping predation risk low, and also because they facilitate a close association with L. polaris from which the whelks receive feeding benefits.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour

[Elsewhere and otherwise.]. / Ailleurs et autrement.

The network of mental health services is constantly in movement. From a relatively simple model it has become a complex service with a multiple ideology, its results are indetermined and have now to be revised. While commenting on the elaboration of a politic in mental health, the authors describe an experience where the mental health services in a Montreal region were diversified and reorganised in sub-regions. They then give an idea of the situation, the arms hoped for, the organisational mode, and the sub-regions; the main problems encountered are identified as well as the stakes and the areas of action. They uncover the particularities and the different realities that are the mainstay of the Greater Montreal.

[To become someone.]. / Devenir quelqu'un.

The author in this article tells in simple but eloquent terms of the establishment of a farm designed to welcome asylum patients. With the help of a case history, Real's, he describes life at the farm, the possibilities and difficulties of integration.

[The " Agent de quartier " : information and help service to the community.]. / Le service d'information et d'aide à la communauté «L'Agent de quartier¼

This article describes the process of instituting in a community a mental health preventive program that had originated in a third line psychiatric institution. The author describe the different stages of the project as much from the point of view of the workers'experiences, the ideological evolution, the organisational modalities as from its impact on the network of the mental health distribution services. The implantation of this new service was not easy for the community nor for the initiators. Luckily, the efforts encountered were worth while since the need for such a service is now recognised.