Position preferences within groups: do whirligigs select positions which balance feeding opportunities with predator avoidance?

Romey, William L.

doi:10.1007/s002650050181

Cited by 20 publications

(33 citation statements)

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“…The link between resource availability, predation risk, and foraging success is individual behaviour, and adjustments in foraging patterns or differences in phenotypic traits among individuals can come into play in determining foraging success. For instance, if hungry foragers prefer a certain position in the group, their capture rate at this position may be higher even if resource availability is unrelated to spatial position (Krause et al 1992;Romey 1995). Foragers may compete for better positions which may alter the costs and benefits of occupying certain positions (Murton et al 1971;Black et al 1992).…”

Section: Introductionmentioning

confidence: 99%

Low Foraging Success of Semipalmated Sandpipers at the Edges of Groups

Beauchamp

2005

Ethology

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Variation in foraging success in relation to spatial position in a group is little known in species that feed on mobile prey that can hide or flee upon disturbance by foragers. I examined the foraging success of individuals located either at the edge or at the centre of flocks of semipalmated sandpipers (Calidris pusilla) feeding on a burrowing amphipod (Corophium volutator) during migration stopover in the Bay of Fundy, Canada. The rates of pecking, prey capture and success were lower for individuals foraging at the edge than at the centre of flocks. Edge birds spent more time running and more time flying than centre birds. Edge birds moved away from the centre of the flock and made frequent short flights towards the centre. In contrast, centre birds rarely moved in a specific direction and flew mostly to relocate elsewhere with the whole flock. Sandpiper flocks foraged over a large area in a relatively short amount of time. In addition, amphipod density is high in this habitat. It thus appears unlikely that prey depletion or low food availability at the edges of groups could explain the spatial variation in foraging success. Low foraging success at the edges of flocks thus arose mainly because of time costs related to flock expansion and retraction. The effect of mutual interference among foragers and of predation risk by falcons is discussed with respect to flock expansion and retraction.

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Section: Introductionmentioning

confidence: 99%

Low Foraging Success of Semipalmated Sandpipers at the Edges of Groups

Beauchamp

2005

Ethology

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“…Commonly, two of its major benefits have been argued to be a lower predation hazard and an increased efficiency of foraging (Hamilton 1971;Caraco & Pulliam 1984;Clark & Mangel 1986;Elgar 1989). These benefits, however, are not necessarily shared equally among all group members (Rohwer & Ewald 1981;Schneider 1984) and may depend on the spatial position occupied within the group (Krause 1994;Romey 1995). It is widely accepted, for instance, that being at the edge of a group can be more hazardous in terms of predation (Hamilton 1971) than being in the middle, and that socially dominant individuals prefer the safe central positions of a foraging group (Murton et al 1971;Schneider 1984;Hegner 1985;Elgar 1989;Krause 1994).…”

Section: Introductionmentioning

confidence: 99%

Geometry for a selfish foraging group: a genetic algorithm approach

Barta

Flynn

Giraldeau

1997

Proc. R. Soc. Lond. B

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SUMMARYThe advantages of group living are not shared equally among all group members, and these advantages may depend on the spatial position occupied by a forager within the group. For instance, it is thought that socially dominant individuals prefer the predator-safe central position of groups forcing subordinates to the periphery. Uneven spread of benefits among group members can occur when some animals (the scroungers) parasitically exploit the food findings of other foragers (the producers). Here we focus on how playing producer or scrounger affects an individual's spatial position within a group. We model the movement of foraging animals playing scrounger or producer using a spatially explicit simulation, and use a genetic algorithm to establish movement rules. We find that groups containing producers and scroungers are more compact compared to an equivalent group of producers only. Furthermore, the position occupied by strategies varies: scroungers are mainly found in central positions, with producers in the periphery, suggesting that the best position for strategies differs. Dominants, therefore, should prefer movement rules which lead to central positions because of the positional benefits provided to the scrounger strategy they use. Moreover, position within a group will introduce an asymmetry among otherwise phenotypically symmetric individuals.

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“…), e.g. spider groups arranged according to level of aggression (Rayor & Uetz 1993), whirligig beetles sorted according to how they balance predation risk with hunger level (Romey 1995), and laboratory fish according to hunger level (Krause et al 1992). Our results provide in situ empirical support for the hypo- …”

Section: Discussionmentioning

confidence: 54%

Adaptive mass formations in fish shoals founded in conflicting motivation

Johnsen

Skaret²

2008

Mar. Ecol. Prog. Ser.

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The organising principles behind adaptive collective formations in animals are not well understood. Here we document that persistent vertical hourglass formations occur during the critical spawning period in huge shoals of the herring Clupea harengus spawning demersally. We compared individual maturity stage between the upper and lower components of the formations and found the proportion of spawners to pre-and post-spawners to be significantly higher in the lower than in the upper components. Our results provide empirical support for the hypothesis that these formations are a collective output of individual risk assessment in a compromise between survival and reproduction, where non-spawners minimise the time spent in the demersal zone, where density of gadoid predators was found to be highest. Conflicting individual motivation may thus be an organising principle behind mass formations in fish shoals. KEY WORDS: Herring · Spawning · Hourglass formation · MotivationResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 358: 295-300, 2008 spawners to be lowest in the low component of the hourglasses and the density of predators to be highest near the bottom. MATERIALS AND METHODSWe analysed time series of acoustic data from the Norwegian spring spawning (NSS) herring Clupea harengus spawning areas along the Norwegian coast, where each spring herring are found in some of the largest known animal aggregations on the globe. The acoustic data material was acquired in February and March 1994 to 2006 (except for the years 1996 in part as abundance estimate surveys of NSS herring, and in part as distribution mapping and/or behavioural studies within selected herring spawning sites (Fig. 1). In total, 260 trawl stations were available, and acoustic data were collected during 170 d at sea for an area covering roughly 30 000 nautical miles (n miles).The collection of data was carried out by experienced personal and followed a standard scheme: Acoustic recording was done with a 38 kHz SIMRAD EK 500 echo sounder and integrator (replaced with EK 60 in 2005) and post-processed using the Bergen Echo Integrator (BEI) (Foote et al. 1991). Acoustic signal characteristics combined with trawl catches were used for reference when allocating acoustic densities to species. All biological samples were obtained by pelagic trawl upon recordings of herring and not at random or fixed stations. If permitted by the size of the catch, 100 herring were randomly sampled from each trawl haul. Herring with maturing and mature gonads were categorised as 'pre-spawners', individuals with running gonads as 'spawners' and individuals with empty or quasi-empty gonads as 'post-spawners'. The acoustic density values were stored by species in nautical area scattering coefficient (NASC) units (MacLennan et al. 2002) in a database with a horizontal resolution of 1 n mile and a vertical resolution of 10 m, referenced to the surface.In order to distinguish potential hourglass formations, we first searched...

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Position preferences within groups: do whirligigs select positions which balance feeding opportunities with predator avoidance?

Cited by 20 publications

References 0 publications

Low Foraging Success of Semipalmated Sandpipers at the Edges of Groups

Low Foraging Success of Semipalmated Sandpipers at the Edges of Groups

Geometry for a selfish foraging group: a genetic algorithm approach

Adaptive mass formations in fish shoals founded in conflicting motivation

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