Public information for the assessment of quality: a widespread social phenomenon

We propose that the use of public information about the quality of environmental resources, obtained by monitoring the sampling behaviour of others, may be a widespread social phenomenon allowing individuals to make faster, more accurate assessments of their environment. To demonstrate this (i) we define public information and distinguish it from other kinds of social information; (ii) we review empirical work demonstrating the benefits and costs of using public information to estimate food patch quality; (iii) we examine recent work showing that individuals may also be using public information to improve their estimates of the quality of such disparate environmental parameters as breeding patches, opponents and mates; and finally (iv) we suggest avenues of future work to better understand the nature of public information use and when it might be used or ignored. Such work should lead to a more complete understanding of the behaviour of individuals in social aggregations.     

Potential disadvantages of using socially acquired information

The acquisition and use of socially acquired information is commonly assumed to be profitable. We challenge this assumption by exploring hypothetical scenarios where the use of such information either provides no benefit or can actually be costly. First, we show that the level of incompatibility between the acquisition of personal and socially acquired information will directly affect the extent to which the use of socially acquired information can be profitable. When these two sources of information cannot be acquired simultaneously, there may be no benefit to socially acquired information. Second, we assume that a solitary individual's behavioural decisions will be based on cues revealed by its own interactions with the environment. However, in many cases, for social animals the only socially acquired information available to individuals is the behavioural actions of others that expose their decisions, rather than the cues on which these decisions were based. We argue that in such a situation the use of socially acquired information can lead to informational cascades that sometimes result in sub-optimal behaviour. From this theory of informational cascades, we predict that when erroneous cascades are costly, individuals should pay attention only to socially generated cues and not behavioural decisions. We suggest three scenarios that might be examples of informational cascades in nature.     

Herbivory and population dynamics of invasive and native <Emphasis Type="Italic">Lespedeza</Emphasis>

Some exotic plants are able to invade habitats and attain higher fitness than native species, even when the native species are closely related. One explanation for successful plant invasion is that exotic invasive plant species receive less herbivory or other enemy damage than native species, and this allows them to achieve rapid population growth. Despite many studies comparing herbivory and fitness of native and invasive congeners, none have quantified population growth rates. Here, we examined the contribution of herbivory to the population dynamics of the invasive species, Lespedeza cuneata, and its native congener, L. virginica, using an herbivory reduction experiment. We found that invasive L. cuneata experienced less herbivory than L. virginica. Further, in ambient conditions, the population growth rate of L. cuneata (λ = 20.4) was dramatically larger than L. virginica (λ = 1.7). Reducing herbivory significantly increased fitness of only the largest L. virginica plants, and this resulted in a small but significant increase in its population growth rate. Elasticity analysis showed that the growth rate of these species is most sensitive to changes in the seed production of small plants, a vital rate that is relatively unaffected by herbivory. In all, these species show dramatic differences in their population growth rates, and only 2% of that difference can be explained by their differences in herbivory incidence. Our results demonstrate that to understand the importance of consumers in explaining the relative success of invasive and native species, studies must determine how consumer effects on fitness components translate into population-level consequences. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Mate choice copying as public information

We outline a framework that views mate choice copying as public information. In this framework, all individuals assess the quality of potential mates. Individuals can benefit by copying when they cannot discriminate differences in potential mates, as copying can result in better discrimination. This framework predicts that the discrimination ability of individuals will strongly determine the frequency of copying behaviour observed: individuals with poor discrimination ability should often copy, whereas individuals with superior discrimination ability should rarely copy. Copying behaviour may occur in a wide variety of taxa but only be observed when individuals are presented with difficult discrimination tasks.     

Information for patch assessment: a field investigation with black-chinned hummingbirds

I examined the kinds of information black-chinned hummingbirds(Archilochus alexandri) used when exploiting artificial resourcepatches in the field. I determined whether birds (1) only usedcurrent patch-sample information or (2) combined current patch-samplewith prior information (the distribution of resources amongpatches) to estimate patch quality, and (3) whether the kindsof information used depended on environmental variability. Iestablished two environments that differed in amount of variationin patch subtypes and determined the use of information by assessingthe correlation between the number of rewards obtained and thenumber of consecutive unrewarded patch probes just before patchdeparture. In the low-variance environment, most birds appearedto combine prior information with patch-sample information.Individuals using prior information foraged more efficientlythan those that did not. In the high-variance environment, somebirds appeared to combine patch-sample information with priorinformation, whereas others apparently relied solely on patch-sampleinformation to estimate patch quality, with no difference inforaging efficiency. In both environments, prior informationwas used after approximately 25 patches were exploited.