Selection by passerine birds is anti-apostatic at high prey density

Allen, J. A.; Anderson, Keith

doi:10.1111/j.1095-8312.1984.tb00142.x

Cited by 48 publications

(32 citation statements)

References 16 publications

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“…Experiments with artificial pastry prey have shown that wild birds tend to remove disproportionately more common forms when prey density is low while at very high densities they tend to eat disproportionately more rare forms (Allen 1972(Allen , 1976Horsley et al 1979;Allen and Anderson 1984;Church et al 1997). The evolutionary consequences of such selection on real prey would be to promote polymorphism within populations at low density and monomorphism when the density is much higher (Clarke 1962;Greenwood 1984Greenwood , 1985.…”

Section: Introductionmentioning

confidence: 99%

The influence of density on frequency-dependent food selection: a comparison of four experiments with wild birds

Weale¹,

Whitwell²,

Raison³

et al. 2000

Oecologia

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We compare the results of four experiments, conducted at different times and with different protocols, that explored the relationship between frequency-dependent selection and prey density in wild birds feeding on artificial populations of coloured baits. One (experiment 4) used pastry baits that differed only in the presence or absence of a red stripe, and this experiment provided no evidence for any kind of selective behaviour. The other three experiments used green and brown baits, and they all provided evidence for a trend towards increasing anti-apostatic selection with high densities (>100 baits m). However, one of these (experiment 3) provided no evidence for frequency-dependent selection at low densities (0.5-20 baits m), while the other two experiments concurred in suggesting a trend towards increasing apostatic selection with low densities (down to 2 baits m). Together, these experiments both support and qualify the published findings of experiment 1 that frequency- dependent selection by wild birds on bait populations is modified by density. Experiment 4 indicates that frequency-dependent selection may break down entirely if bait types are too similar, while experiment 3 indicates that some details of this trend with density will depend either on the protocol used or on exogenous changes in the birds' feeding behaviour.

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Section: Introductionmentioning

confidence: 99%

The influence of density on frequency-dependent food selection: a comparison of four experiments with wild birds

Weale¹,

Whitwell²,

Raison³

et al. 2000

Oecologia

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show abstract

“…By contrast, when the`baits' are presented at very high density (410 000 m 72 ), they remove disproportionately more of the rare form (Allen 1972;Horsley et al 1979;Allen & Anderson 1984). Thus, the selection by wild birds is frequency dependent and its direction is in£uenced by prey density.…”

Section: Introductionmentioning

confidence: 99%

“…One possible cause of anti-apostatic selection is that individual predators tend to remove rare forms because they stand out from the background of the rest (Allen 1972). Another possible cause of anti-apostatic selection at the population level is from variability in frequency-independent selection among individual predators (P. Chesson 1984;Sherratt & MacDougall 1995), and there is some evidence for such variability from the behaviour of wild blackbirds feeding on pastry prey at very high density (Allen & Anderson 1984).…”

Section: Introductionmentioning

confidence: 99%

The influence of density on frequency–dependent selection by wild birds feeding on artificial prey

Allen

Raison

Weale

1998

Proc. R. Soc. Lond. B

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Previous work has demonstrated frequency-dependent selection by wild garden birds when feeding on green and brown pastry`baits'. When the density of baits is low, the common colour is eaten disproportionately more than the rare colour (apostatic selection), and when the density is very high, the rare colour is eaten disproportionately more than the common (anti-apostatic selection). We explored the relationship between frequency-dependent predation and density in an experiment at 16 separate sites, using four levels of density and two frequencies of green and brown. Analysis of estimates of log relative risk ratios showed little evidence for frequency-independent selection, but frequency-dependent selection changed gradually from apostatic at low density to anti-apostatic at high density. The validity of these conclusions in terms of individual bird behaviour was con¢rmed by Monte-Carlo simulations. We thus conclude that selection by wild birds feeding on green and brown arti¢cial prey is frequency dependent, and that the strength and direction of this selection changes with prey density in a gradual and predictable manner.

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“…1a), following the techniques of Allen et al (1990), Allen and Anderson (1984) and Greenwood et al (1984). In the``aggregated'' treatments, the prey were arranged into ®ve high-density clumps (one in the centre and one near to each corner), with a frequency of 9:1 (18:2) present in each clump (Fig.…”

Section: Methodsmentioning

confidence: 99%

Does prey dispersion affect frequency-dependent predation by wild birds?

1997

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Despite the fact that the vast majority of natural prey items are dispersed in a non-random manner, few studies of frequency-dependent selective predation have explicitly examined the effect of prey dispersion on selectivity. We examined the effect of prey dispersion on the direction and strength of frequency-dependent selection by wild birds feeding on artificial prey (green or brown pastry baits). In a series of four experimental manipulations, we tested for the occurrence of frequency dependence with two different dispersion patterns (random or clumped). Manipulations were carried out at one of two absolute densities (25 prey m or 100 prey m), and were repeated at different sites in Southampton, England and Aljarafe, Spain. Our results suggest that prey dispersion has no effect on either frequency-dependent or -independent preferences. One possible explanation for this is that the birds had virtually complete information about prey frequencies at the relatively high densities used and based their preferences on their overall perception of availability. However, we cannot rule out the possibility that dispersion may influence selectivity when prey are cryptic or available at lower absolute densities. Although there was no effect of dispersion, frequency-dependent selection was, overall, significantly anti-apostatic (i.e. rare baits were more preferred than common baits). This anti-apostatic effect was stronger in Southampton than Aljarafe and stronger at 100 prey m than 25 prey m. The differences in the strength of selection between the two locations was interpreted in terms of (i) whether the avian predators foraged in flocks or not, and (ii) the number of different species present (and, consequently, the variation in preference among individual birds).

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Selection by passerine birds is anti-apostatic at high prey density

Cited by 48 publications

References 16 publications

The influence of density on frequency-dependent food selection: a comparison of four experiments with wild birds

The influence of density on frequency-dependent food selection: a comparison of four experiments with wild birds

The influence of density on frequency–dependent selection by wild birds feeding on artificial prey

Does prey dispersion affect frequency-dependent predation by wild birds?

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