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1.  The effect of social facilitation on foraging success in vultures: a modelling study 
Biology Letters  2008;4(3):311-313.
The status of many Gyps vulture populations are of acute conservation concern as several show marked and rapid decline. Vultures rely heavily on cues from conspecifics to locate carcasses via local enhancement. A simulation model is developed to explore the roles vulture and carcass densities play in this system, where information transfer plays a key role in locating food. We find a sigmoid relationship describing the probability of vultures finding food as a function of vulture density in the habitat. This relationship suggests a threshold density below which the foraging efficiency of the vulture population will drop rapidly towards zero. Management strategies should closely study this foraging system in order to maintain effective foraging densities.
PMCID: PMC2610049  PMID: 18364309
local enhancement; Allee effect; food finding; scavenging; scrounging; social facilitation
2.  Fatal attraction: carnivorous plants roll out the red carpet to lure insects 
Biology Letters  2008;4(2):153-155.
We provide the first experimental test of the hypothesis that the coloration of carnivorous plants can act as a signal to lure insects and thus enhance capture rates. An experimental approach was needed to separate effects of the visual appearance of plants from those of traits that may correlate with appearance and also affect capture rates. We compared insect capture rates of pitcher plants with artificially coloured red and green pitchers in a paired design, and found that plants with red pitchers captured significantly more flying insects. Thus, we present the first experimental evidence of visual signalling in carnivorous plants. Further, it has previously been suggested that carnivorous plants use contrasting stripes or UV marks on their pitchers to lure insects; our results emphasize that insect traps do not need to sport contrasting colours to be attractive; it might be sufficient to be different from the background.
PMCID: PMC2429934  PMID: 18198137
plant–animal interactions; visual signalling; insect vision; anthocyanins; traps
3.  Avian predators attack aposematic prey more forcefully when they are part of an aggregation 
Biology Letters  2006;2(4):488-490.
Defended insects often advertise their unprofitability to potential predators using conspicuous aposematic coloration. Many aposematic insects are also gregarious, and it has been suggested that the aggregation of defended prey may have facilitated the evolution of aposematic coloration. Empirical studies have demonstrated that birds are more wary of aggregated aposematic prey, and learn to avoid them more quickly than solitary prey. However, many aposematic insects survive being attacked by birds, and the effect of aggregation on post-attack survival has not previously been investigated. Using domestic chicks as predators and artificially manipulated mealworms as prey, we provide empirical evidence that predators attack aggregated aposematic prey more forcefully than solitary prey, reducing the likelihood of prey surviving an attack. Hence, we suggest that previous works concluding that aggregation was an important pre-requisite for the evolution of aposematism may have overestimated the fitness benefits of aggregation, since aggregated prey may be attacked less but are also less likely to survive an attack.
PMCID: PMC1833999  PMID: 17148269
aposematism; receiver psychology; insects
4.  Increasing search rate over time may cause a slower than expected increase in prey encounter rate with increasing prey density 
Biology Letters  2005;1(2):133-135.
A previous experiment with birds searching for caterpillars in an aviary demonstrated a highly counterintuitive result, that the rate at which a forager encounters prey does not increase linearly with prey density. Here, I demonstrate that if search rate increases over time then this can produce exactly the observed type of behaviour. Further, I argue that declining perception of predation risk over time in the absence of reinforcement, coupled with a trade-off between anti-predator vigilance and searching ability (both widely reported in field and laboratory studies), could generate such a change in search rate over time. Hence, if my hypothesis is correct, the previous experimental results could have considerable generality, and invite reconsideration of our mathematical descriptions of predator–prey interactions.
PMCID: PMC1626228  PMID: 17148147
foraging; searching; predation risk; trade-off

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