Behavioral Ecology Vol. 15 No. 2: 269–277
DOI: 10.1093/beheco/arh008
The role of conformity in foraging when
personal and social information conflict
Rachel L. Kendal, Isabelle Coolen, and Kevin N. Laland
Subdepartment of Animal Behaviour, Department of Zoology, University of Cambridge,
Madingley, Cambridge CB3 8AA, UK
There is currently considerable interest in the interplay between personal and social information in decision-making processes.
Two experiments are presented exploring the relative use of prior personal information and subsequent social information in
foraging decisions of guppies. Experiment 1 tested the assumption that when the use of information acquired through personal
experience is not costly, conflicting social information will be ignored. The assumption was confirmed because, when given
a choice between feeding at two food patches, at one of which they had previously seen conspecifics feed, individual fish with
prior experience of feeding at the alternative site chose the alternative, whereas fish with no prior experience chose the site at
which their conspecifics had fed. Experiment 2 tested theoretical predictions that when the use of information acquired through
personal experience is potentially costly, conflicting social information will be weighed more heavily than will personal
information. The prediction was confirmed because, when given a choice between feeding at two food patches, one at which they
had previously seen conspecifics feed and one behind a visual barrier, individual fish with prior experience of feeding behind the
barrier chose the site at which their conspecifics had fed. These findings suggest that conformity can promote social learning in
naı̈ve individuals, but prior experience can insulate individuals from conformity provided the costs of relying on that experience
are small. In addition, the experiments highlight the fact that personal and social information are not always weighed equally. Key
words: conformity, guppy, personal information, social foraging, social learning. [Behav Ecol 15:269–277 (2004)]
common feature of social foraging is that the food
discoveries of a few lead to the feeding of many, and as
a result, group living may enable individuals to forage more
efficiently through information transfer and social learning
(Heyes and Galef, 1996; Ward and Zahavi, 1973; Zentall and
Galef, 1988). This is because when there is temporal or spatial
variation in habitat quality, animals must continually assess
aspects of their environment (Mangel, 1990; Yoerg, 1991),
and social animals commonly have access to a greater amount
of relevant information than do solitary ones, as they can
observe the activities, successes, and failures of others
(Templeton and Giraldeau, 1995a, 1996). In addition,
although large groups may attract predators, they may also
reduce per capita predation pressures through increased
group vigilance, dilution, confusion, and selfish-herd mechanisms (Bertram, 1978; Hamilton, 1971; Pulliam, 1973).
Information transfer and social learning has long been of
interest to ethologists and behavioral ecologists because such
processes appear to enable onlookers to exploit information
gained by others and allow animals to learn about their
environments rapidly and efficiently, without making costly
mistakes or wasting time on exploration. Through social
learning, animals may learn how (observational learning) to
deal with a resource or where (local enhancement) it is
located, whereas through the use of ‘‘public information’’
(Valone, 1989) animals may learn about the quality of an
environmental resource. Although these distinctions are useful, the latter term is arguably overly restrictive as all forms
of social learning involve the use of socially acquired
information (Giraldeau, 1997; Giraldeau and Caraco,
A
Address correspondence to R. L. Kendal, who is now at the
Department of Biological Sciences, Stanford University, Stanford, CA
94305, USA. E-mail: [email protected]. K. Laland and I.
Coolen are now at The Centre for Social Learning and Cognitive
Evolution, School of Biology, St. Andrews University, UK.
Received 11 September 2002; revised 4 April 2003; accepted 29
April 2003.
2000). Here, we use ‘‘public information’’ in Valone’s more
restrictive sense and follow Valone and Templeton’s (2002)
recommendation in using the more general term ‘‘social
information’’ when referring to all information acquired
from, or as a consequence of observation of or interaction
with, other animals.
Under natural conditions the use of social information is
not the only means by which animals make decisions. Theoretical analyses suggest that species living in an environment of
intermediate variability will be likely to use social learning,
whereas those living in a highly variable or in a stable environment, with less to gain from observing others, should rely
upon asocial learning or genetic inheritance of information,
respectively (Boyd and Richerson, 1985, 1988; Laland et al.,
1996). Social learning is thought to be favored at intermediate
rates of environmental variability, as individuals can acquire
relevant information without bearing the costs of direct interaction with the environment associated with asocial learning,
but with greater phenotypic flexibility than if the behavior was
unlearned (Boyd and Richerson, 1985, 1988). A common, but
untested, assumption of these theoretical analyses is that individuals will be more likely to rely on social information if they
lack the requisite personal information to guide their decisionmaking than if they possess relevant personal information
(see Boyd and Richerson, 1988).
Individual foragers may use personal information, such as
(1) prior knowledge, described variously as pre-harvest or
prior information that is available before patch exploitation
(Valone, 1991, 1992), and (2) ‘‘harvest’’ or ‘‘sample’’ information that is acquired during the actual exploitation of
a patch. How animals weight personal and social information
is unknown, although theoretical analyses commonly assume
that personal and social information are weighted equally
(Clark and Mangel, 1984; Templeton and Giraldeau, 1995a,
1996; Valone and Giraldeau, 1993). However, there may be
many situations in which a forager would benefit by weighting
one or other type of information above the other. For
example, the value of social information may depend upon
Behavioral Ecology vol. 15 no. 2 International Society for Behavioral Ecology 2004; all rights reserved.
Behavioral Ecology Vol. 15 No. 2
270
Figure 1
Diagram of the tank showing
the partitions used throughout
the experiments numbered as
in the text (a) (Methods, experiment 1; dashed lines indicate
transparent partitions; solid
lines, opaque partitions); the
division of the tank into zones,
where the lettering would be
reversed were the feeder on the
right to be baited with bloodworm (b); and the set-up during training of the shoals,
showing the four feeders at
either end of the tank and the
partitions used (c).
the cost of acquiring or using personal information, owing to
missed foraging opportunities or encountering dangers (Boyd
and Richerson, 1985, 1988).
It is now well established that the use of social information
can enhance foraging efficiency in shoaling fish (Day et al.,
2001; Laland and Williams, 1997, 1998; Pitcher and House,
1987; Ryer and Olla, 1992). Lachlan et al. (1998) suggest that
in fish a tendency to shoal with the largest number of
individuals may generate a positive frequency-dependent
transmission of foraging information, or ‘‘conformity’’ (Boyd
and Richerson, 1985). Day et al. (2001) found that, in the
guppy, conformity hindered the performance (and subsequent social learning) of a foraging innovation that
required the loss of visual contact with the shoal. In the
current study, the circumstances under which individuals
favor personal over social information (or vice versa) are
examined by using the previously established effect of opaque
barriers upon positive frequency-dependent social learning in
guppies (see Day et al., 2001). In contrast to other studies that
have compared the use of sample and social information
(Smith et al., 1999; Templeton and Giraldeau, 1995a, 1996),
here the use of prior personal and social information is
compared, using small laboratory populations of fish. It would
appear that this is the first study conducted to test hypotheses
concerning the relative weighting of prior personal and social
information and the assumptions of Boyd and Richerson’s
(1985, 1988) theoretical models.
Two experiments were conducted that each presented
individual guppies with a choice between feeding at two food
patches, at one of which they had just seen conspecifics feed
or not (social information), depending on the condition, and
an alternative patch in which fish had prior experience of
feeding or not (personal information), depending on the
condition. Experiment 1 tests the assumption that individuals
are disposed to rely on social information when they lack the
requisite personal information to guide decision-making
(Boyd and Richerson, 1988). A finding that naı̈ve fish but
not those with prior personal information behave according
to the social information received would provide the first
empirical confirmation of this assumption. In experiment 2,
the theoretical prediction that individuals will be more reliant
on social information in circumstances in which personal
information is costly to acquire or use is tested (Boyd and
Richerson, 1985, 1988). In this experiment the use of prior
personal information is costly, as it requires fish to swim
behind an opaque barrier and lose visual contact with
conspecifics. A finding that those fish with personal and
social information use the social information more in
experiment 2 (visual barrier) than in experiment 1 (no visual
barrier) would support the theoretical assumption that
reliance upon social information increases when personal
information is costly to acquire or use.
METHODS
The study used laboratory populations of guppies (Poecilia
reticulata), purchased from Neil Hardy Aquatica, London.
Domestic guppies were used as the diverse coloration of these
fish makes identification of both sexes possible without
stressful marking procedures. We know of no evidence that
the behavior of domestic strains of guppy differs significantly
from that of the wild type, and social learning of foraging
behavior has been found in both laboratory (Lachlan et al.,
1998; Laland and Williams, 1997, 1998) and wild populations
of the guppy (Reader et al., 2003). Only females were used to
rule out confounding effects of sexual interactions; the
experimental evidence for social learning in guppies is more
compelling in this sex (Laland and Williams, 1997). At the
start of the experiment, all subjects were experimentally naı̈ve.
Fish were housed in aquarium tanks of dimensions 61 3
30 3 39 cm (length 3 width 3 height), with a water level of
25 cm. Tanks were visually isolated from each other by using
white Perspex. All tanks were equipped with plastic runners
into which sheets of plastic could be placed to partition them
(see Figure 1a) and were visually divided into six zones, the
two feeders at either end of the tank each comprised a zone,
as did each quarter of the tank (see Figure 1b). Boxlike
feeders of 10.5 3 6.53 7.5 cm (length 3 width 3 height) were
used. They were designed so that subjects could not see
whether they contained food until inside them. Fish could
only gain access to the food (freeze-dried blood-worm) by
swimming through a 10.5 3 1.5-cm (high) hole at the bottom
of the feeder and upward to where it floated on the water
surface (see Figure 1c).
Kendal et al.
•
Conformity and personal versus social information
271
Figure 2
Procedure of experiment 1,
showing the personal experience training procedure in
which fish were trained to feed
(food designated as F) from
either blue (B) or yellow (Y)
feeders, in either the upper or
lower part of the tank; the
social experience procedure
in which fish act as both
demonstrators (as shoals of
10) and, when transferred into
the opposing set up tank, as
observers; and the testing procedure in which the demonstration shoal was confined
with opaque partitions while
the observer was released and
its behavior monitored.
Statistical methods
One sample and independent samples chi-square tests were
used to analyze the feeder choices of fish within and between
conditions, respectively. All statistical tests were two-tailed.
When sample sizes for conditions within an experiment differ,
unless stated otherwise, this is owing to the death of a subject
part way through the study.
Experiment 1: Absence of visual barrier
Subjects were allocated at random to three conditions: (1)
trained observers, who experienced prior personal and subsequent conflicting social information; (2) naı̈ve observers,
who experienced social information only; and (3) controls,
who experienced neither prior personal nor social information. At test, all subjects were given a choice between feeding
at two food sites, one at which only trained observers had
prior personal experience of feeding and a second at which
trained observers and naı̈ve observers had observed conspecifics feed.
Subjects and apparatus
Twenty adult female guppies acted as trained observers, 30 as
naı̈ve observers, and 29 as controls. In addition, 20 females
acted as shoal mates to create shoals of 10 fish in the trained
observer tanks.
Two tanks contained naı̈ve observers (in groups of 15), two
contained controls (in groups of 15), and four contained
shoals of 10 trained observers (of which five from each tank
were tested). The short sides of the trained observer tanks were
colored either yellow or blue, using paper attached to the
outside of the tanks. The use of these colors was counterbalanced across tanks and provided cues to assist training of
the fish. During the training period, the naı̈ve observers and
controls were exposed to white opaque feeders, whereas the
trained observers were exposed to identical feeders colored
blue and yellow.
Procedure
The experiment involved a personal experience (training
period), a social experience (demonstration period) and a test
(Figure 2).
Personal experience training period
Personal training of trained observers occurred over a 7-day
period. Subjects were given a total of 15 trials, at a maximum
of three trials a day. To ensure that the subjects would be
motivated to feed during the test period, the number of
training sessions per day decreased, such that on days 1, 2,
and 3, three were given; on days 4 and 5, two were given; and
on days 6 and 7, one was given.
To familiarize the trained observers with the test procedure,
they were constrained before introduction of the feeders.
Trained observers were shepherded into one half of the tank,
which was divided lengthwise by using a transparent plastic
partition (61 3 30 cm high; partition 1 (Figure 1a) and then
constrained in the central portion of the remaining tank area
by using two transparent partitions (15 3 30 cm high; partitions 2 and 3) placed 15 cm from either short end of the tank.
Opaque partitions (partitions 4 and 5) were placed outside of
the transparent partitions to ensure subjects could not observe
the introduction of the feeders. The feeders were positioned
in the appropriate end of the tank according to the color cues,
and blood-worm was placed in the feeder to which the fish
were to be trained (the experimenter carried out a motion as if
to provision the other feeder with food, preventing the fish
from using the behavior of the experimenter as a cue). In total,
four feeders were placed in the tank, one of each color on
either side of the length-way partition (partition 1) (Figure
1c). The partitions constraining the fish centrally (partitions 2,
3, 4, and 5) were simultaneously removed and the fish allowed
to feed for a maximum of 10 min.
The direction and color to which fish were trained to feed
was counterbalanced (left-blue [LB], left-yellow [LY], rightblue [RB], right-yellow [RY]). LB- and LY-trained fish were
always constrained (by partition 1) in the portion of the tank
272
Behavioral Ecology Vol. 15 No. 2
Figure 3
Procedure of experiment 2,
showing the personal experience training of observers to
feed (food designated as F)
from either blue (B) or yellow
(Y) feeders, behind an opaque
barrier and demonstrators to
feed at the open end of the
tank; the social experience
procedure for fish in all three
conditions; and the identical
test period for all conditions,
in which observers must lose
visual contact with the constrained demonstrator shoal
in order to feed at the trained
feeder.
furthest from the experimenter during training, whereas RBand RY-trained fish were always constrained in the portion of
the tank nearest the experimenter during training (Figure 2).
This training procedure allowed LB-trained fish to be tested
in a physically identical area of the RY-trained tank (and vice
versa), and LY-trained fish to be tested in a physically identical
area of the RB-trained tank (and vice versa).
During this period naive observers and controls were
exposed to white feeders placed in random positions within
the tank. After 7 days of 10-min presentations, all fish in the
naı̈ve observer and control tanks were competent at entering
the feeders and appeared to associate them with food.
Social experience and test
For each trained observer tank in turn, fish were shepherded
into the central portion of the tank to act as demonstrators in
the trained observer condition. An observation area was
created by using transparent partitions (partitions 6 and 7)
placed in alignment with partitions 2 and 3 in the empty half
of the tank (Figure 1a). A trained observer, now acting as an
observer, was removed from a different tank and placed into
this area. Fish from the two tanks LY and RB and those from
the two tanks LB and RY acted as demonstrators and observers
for each other (Figure 2). All fish were allowed a settling
period of 2 min before the four feeders were introduced to
the tank, as described for training, and blood-worm was
placed in all of them. Demonstration began when the shoal of
10 fish were released. To ensure that the demonstrators ate
only from the alternative colored feeder to that which the
observer had been trained, the transparent partition allowing
access to this feeder was left in place. The quality of
demonstration was assessed by recording the number of
demonstrators that were in each zone of the tank at every 10 s
for the duration of the 3-min demonstration (Figure 1b).
After demonstration, the shoal was shepherded into the
central area of its half of the tank. Opaque partitions
prevented the shoal seeing the color cues and thus continuing
to demonstrate a preference for one end of the tank by
aggregating at one end of the central zone. Once all fish had
settled, the observer fish was released from the observation
area (Figure 2). The feeder it entered and the latency with
which it did so was noted. The demonstrator shoal remained
in the tank (constrained but visible) while the observer was
tested in order to alleviate stress associated with isolation.
Fish in the naı̈ve observer condition were also provided with
social experience and tested in the same manner. Four
trained and four naive fish were tested each day. A set of four
fish was tested from 1000–1200 h and from 1500–1700 h.
Within the naive observers and trained observers, morning
and afternoon trials were counterbalanced. Similarly, the
order in which trained observers were tested in the pairs of
identically color-cued tanks was counterbalanced. The control
fish were tested as described above except the demonstrator
shoal remained in the central portion of their half of the tank
for the 3-min demonstration period.
Experiment 2: Presence of visual barrier
In this experiment the cost of using prior personal information is increased by placing an opaque barrier in front of the
feeder at which fish receive personal experience training. Subjects were allocated at random to three conditions; (1) trained
observers, who experienced prior personal and conflicting
social information; (2) trained nonobservers, who experienced
prior personal information only; and (3) controls, who experienced neither prior personal nor social information (Figure
3). The control condition was to verify that losing visual contact with the shoal by going behind the barrier represented
a cost of some kind that fish avoided. The trained nonobserver
condition was to establish whether the behavior of trained
observers was purely related to avoidance of losing contact with
conspecifics or was influenced by the use of social information.
Subjects and apparatus
Twenty-nine guppies acted as trained observers, 29 as trained
nonobservers, and 28 as controls. In addition, 20 fish acted as
demonstrators. Six shoals of 15 fish and two shoals of 10 fish
were established. The latter two shoals were the demonstrator
fish, and the remaining six shoals were trained observers,
trained nonobservers, or controls. Color cues to assist training
Kendal et al.
•
Conformity and personal versus social information
Figure 4
Results of experiment 1, showing the proportion of fish that chose the
demonstrator’s feeder, for trained observer, naı̈ve observer, and
control conditions (* p , .05, ** p , .01, *** p , .001).
comprised yellow and blue paper placed on the left and right
short ends of the tank, respectively. The opaque barrier
comprised a plastic partition 29 3 30 cm (width 3 height)
with a slit vertically through the centre. This was placed (over
the length-way transparent partition 1) 15 cm from the end of
the tank in front of the feeder to which fish were trained
(Figure 3). One side of the partition was colored either yellow
or blue (the other being white) so that the color cue of the
end of the tank was equally salient across experiments.
Procedure
Personal experience training period. The training procedure for
trained observer and trained nonobserver fish was similar to
that of experiment 1. However, to feed from the provisioned
feeder (RB/ LY), fish were required to swim behind a barrier,
which although the same color as the feeder, shielded the
feeder from their view. All fish were constrained in the
portion of the tank nearest to the experimenter (by partition
1) during training (Figure 3). Two demonstrator shoals were
created in the two test tanks. One shoal was trained to feed
from the yellow feeder and the other from the blue feeder. To
reach the provisioned feeder demonstrator, fish were not
required to swim behind the visual barrier, as it was placed (as
described above) in front of the nonprovisioned feeder
(Figure 3).
Social experience and test. The 10 demonstrator fish were
confined in the central portion of the half of the test tank
furthest from the experimenter. A fish trained to feed from
the opposite colored feeder to the demonstrator shoal was
placed into the observation area. Thus, fish from the two LYbarrier training tanks were placed in the RB–no barrier test
tank, and fish from the two RB–barrier training tanks were
placed in the LY–no barrier test tank (Figure 3). Trained
observers saw a 3-min demonstration, whereas trained nonobservers were confined opposite the demonstrators for 3
min. In addition to the measurements taken in experiment 1,
the behavior of the trained fish during demonstration was
measured by noting which zone (of C and D) it was in at every
10 s. As in experiment 1, demonstrator fish were shepherded
back into the central portion of their half of the tank (where
necessary), and after a settling period, the subject fish was
released. In addition to the feeder entered and the latency
taken to do so, the zone the subject was in was noted every 10 s
until it entered a feeder or 15 min had elapsed. The controls
were tested as described for experiment 1.
At the end of each day, training occurred as described
above, in the four trained fish holding tanks, to ensure all
273
Figure 5
The difference in latency (median and interquartile range), in
experiment 1, of trained observers, naı̈ve observers, and controls to
enter a feeder, regardless of whether it was the observer’s or
demonstrator’s trained feeder (* p , .05, *** p , .001).
subjects had equally up-to-date information as to the fact that
food could be found in the feeder behind the barrier.
RESULTS
Experiment 1
Across all demonstration periods, there was a mean 6 SE of
5.7 6 0.18 demonstrator fish in the feeder (zone A), 3.3 6
0.14 fish in the zone immediately surrounding the feeder
(zone B), 0.7 6 0.07 fish in zone C, and 0.3 6 0.03 fish in
zone D (the middle zone nearest the observer’s trained
feeder). All demonstrators were observed to eat at the feeder.
The choice of feeder by the fish in the control condition
was not significantly different to an even distribution (v2 ¼
0.18, df ¼ 1, p ¼ NS). Of the 22 control fish that entered
a feeder, 12 went to that to which the demonstrator shoal had
been trained, whereas 10 went to the opposite feeder. As
several fish did not actually enter a feeder, the zone (B or E)
surrounding the feeder in which they spent the most time was
used to indicate their choice of feeder. Again, the choice of
feeder by the control fish was not significantly different from
an even distribution (v2 ¼ 0.04, df ¼ 1, p ¼ NS), with 14 fish
choosing the feeder to which the demonstrator shoal had
been trained and 15 the opposite feeder. The random
behavior of the control fish suggests that while constrained,
the trained demonstrators did not give off cues influencing
the choice of feeder by the observer fish (Figure 4).
Of the 30 naı̈ve observers, 22 fed from the feeder that had
been used by the demonstrator shoal, whereas eight fed from
the opposite feeder. This preference for the demonstrated
feeder represented a significant departure from that of the
controls (v2 ¼ 4, df ¼ 1, p , .05) (Figure 4). Of the 20 fish in
the trained observer condition, 18 fed from the feeder at
which they had been trained, whereas two fed from the feeder
used by the demonstrator shoal. The preference of the
trained fish for the feeder to which they had been trained was
significantly different from the behavior of the controls (v2 ¼
9.28, df ¼ 1, p , .005) (Figure 4). Trained observer fish fed
significantly faster than did the control fish (Mann-Whitney:
U ¼ 132.5, N1 ¼ 20, N2 ¼ 29, p , .001) (Figure 5). Trained
and naı̈ve observers significantly differed in their choice of
feeder (v2 ¼ 20.4, df ¼ 1, p , .0001) (Figure 4). Trained
observers entered a feeder more rapidly than did naı̈ve
observers (Mann-Whitney: U ¼ 192, N1 ¼ 20, N2 ¼ 30,
p ¼ .032) (Figure 5).
274
Figure 6
Results of experiment 2, showing the proportion of fish that chose the
demonstrator’s feeder, for trained observers, trained nonobservers,
and control conditions. The asterisks directly above the bars indicate
a significant difference from an even distribution, set at 50%
(* p , .05, ** p , .005).
Behavioral Ecology Vol. 15 No. 2
Figure 7
The difference in latency (median and interquartile range) in
experiment 2, of fish in the trained observer, trained nonobserver,
and control conditions, to enter the demonstrators’ (no barrier)
feeder, including those who did not actually enter the feeder
(** p , .01, *** p , .001).
Experiment 2
All demonstrator fish were observed to eat. Across all
demonstration periods, there was a mean 6 SE of 4.7 6
0.15 fish in the feeder (zone A), 3.9 6 0.1 fish in the zone
immediately surrounding the feeder (zone B), 1.1 6 0.08 fish
in zone C, and 0.3 6 0.03 fish in zone D (the middle zone
nearest the observer’s trained feeder).
The choice of feeder by the control fish was significantly
different from an even distribution (v2 ¼ 8, df ¼ 1, p , .005)
(Figure 6). Of the 15 fish that entered a feeder, 13 went to
that which the demonstrator shoal had been trained, whereas
two went to the opposite feeder, behind the visual barrier. As
several fish did not actually enter a feeder, the zone (B or E)
surrounding the feeder in which they spent the most time was
used to indicate their choice of feeder. Again, there was
a significant feeder preference in the naı̈ve fish (v2 ¼ 20.6,
df ¼ 1, p , .001), with 26 fish choosing the feeder to which the
demonstrator shoal had been trained and two the opposite
feeder, behind the visual barrier.
Of the 29 fish in the trained observer condition, 19 fed
from the feeder used by the demonstrator shoal, whereas 10
fed from the opposite feeder, behind the visual barrier, at
which they had received personal experience training. This
preference for the demonstrated (nontrained) feeder approached a significant departure from an even distribution
(v2 ¼ 2.8, df ¼ 1, .1 . p . .05), and was less than expected
when compared with the preference of the control fish for
this feeder (v2 ¼ 6.4, df ¼ 1, .05 . p . .025) (Figure 6).
Trained observer fish fed at the demonstrated feeder (without
barrier) significantly more quickly than did control fish
(Mann-Whitney: U ¼ 94.5, N1 ¼ 19, N2 ¼ 26, p , .001)
(Figure 7).
Of the 29 fish in the trained nonobserver condition, 20 fed
from the feeder opposite to that at which they had received
personal experience training (no visual barrier), and nine fed
from the feeder behind the visual barrier, according to their
personal experience training. This preference for the feeder
to which they had received no personal experience training
was a significant departure from what would be expected
given an even distribution (v2 ¼ 4.2, df ¼ 1, .05 . p . .025),
and was less than expected when compared with the
preference of the control fish for this feeder (v2 ¼ 5.4, df ¼
1, .05 . p . .025) (Figure 6). There was no significant
difference between trained nonobserver and control fish in
the latency to feed at the feeder to which they had received no
personal experience training (without the barrier; MannWhitney: U ¼ 244, N1 ¼ 20, N2 ¼ 26, p ¼ .720) (Figure 7).
The choice of feeder by trained fish in the two conditions
was virtually identical and not significantly different (see
Figure 6). Five of the fish in the trained nonobserver
condition did not enter a feeder within 15 min (their choice
being determined by the feeder zone in which they
significantly spent the most time). In the trained observer
condition, only one fish did not enter a feeder within 15 min,
indicating that fish in the trained nonobserver condition may
have been slower to choose a feeder. Indeed, trained fish who
received a demonstration of the alternative feeder (with no
barrier) took significantly less time to feed at this feeder than
did those who did not receive such a demonstration of the
alternative feeder, both including (Mann-Whitney: U ¼ 80,
N1 ¼ 19, N2 ¼ 20, p ¼ .002) (Figure 7) and excluding fish who
did not actually enter a feeder (U ¼ 62, N1 ¼ 18, N2 ¼ 16, p ¼
.005). There was, however, no significant difference, at test, in
the percentage of time fish in either condition spent in the
zone immediately surrounding the feeder to which they had
not been trained (zone B; t test: t ¼ 0.432, df ¼ 56, p ¼ .667)
or the feeder to which they had been trained (zone E, behind
barrier; t ¼ 0.394, df ¼ 56, p ¼ .695). Trained observers and
trained nonobservers spent (mean 6 SE) 45.7 6 5.8% and
49.1 6 5.4% of the test period in zone B and 15.9 6 4.1% and
13.8 6 3.5% in zone E, respectively. When the analysis was
repeated using only fish who entered the nontrained feeder
(no barrier), there was no significant difference in the
percentage of time, at test, that fish in either condition spent
in the zone immediately surrounding the nontrained feeder
(zone B; t test: t ¼ 0.310, df ¼ 32, p ¼ .759) and the feeder to
which the fish had received personal experience training
(zone E, behind barrier; t ¼ 1.132, df ¼ 32, p ¼ .266).
During the observation period, the number of 10-s intervals
that trained observers were seen to be in the zone (C) closest
to the feeding demonstrators did not significantly differ from
an even distribution regardless of which feeder was entered at
test (v2 ¼ 3.47, df ¼ 1, .1 . p . .05). Fish that chose the
feeder to which they had been trained rather than the
demonstrated feeder spent (mean 6 SE) 12.5 6 1.3 10-s
intervals in zone C, whereas those that chose the demonstrated feeder spent 9.7 6 1 intervals in this zone.
Kendal et al.
•
Conformity and personal versus social information
Comparison of experiments 1 and 2
There was a significant difference in the feeder choices of the
two trained observer conditions between experiments 1 and 2
(v2 ¼ 16.2, df ¼ 1, p , .0001) (cf. Figures 4 and 6). In
experiment 1 (feeder in open tank), trained fish fed from the
feeder at which they had received personal experience
training more than expected, whereas in experiment 2
(feeder behind barrier), trained fish fed at this feeder less
than expected, preferring to feed at the demonstrated feeder
(with no barrier).
DISCUSSION
Experiment 1 clearly shows that the fish lacking prior
personal information (naı̈ve observers) used the social
information provided by the demonstrator shoal, whereas
those with prior personal information (trained observers)
relied upon this rather than upon social information. In
contrast, in experiment 2, fish in the trained observer
condition favored the social information provided by the
demonstrator shoal over their prior personal information as
to the location of food, as use of the latter necessitated loss of
visual contact with the shoal, which we interpret as incurring
(or potentially incurring) a cost.
The preference of naı̈ve observer fish for the demonstrated
feeder, in experiment 1, indicates that when guppies have no
prior information and cannot obtain sample information
without some cost (swimming to and entering feeders), they
will use social information. More generally, the findings of the
experiment suggest that animals may be disposed to rely on
social information when they lack the requisite personal
information to guide decision-making (Boyd and Richerson,
1988). Although this experiment was not designed to
ascertain the psychological processes that allowed naı̈ve fish
to use social information, the most parsimonious explanation
is in terms of local enhancement. As local enhancement
merely represents an attraction to a particular locality, it is not
in itself learning. However, as the naı̈ve observers chose
a feeder after observing demonstration, the local enhancement must have led to social learning as they subsequently
remembered the location of food. The fact that naı̈ve
observers fed at the demonstrated feeder more than expected
when compared with naı̈ve fish without a demonstration
(controls) provides further support to the argument that the
naı̈ve observers had learned the location of food from the one
demonstration they received. In comparison, asocial learning
processes fully account for the behavior of the trained
observers.
In experiment 1, the trained observer fish preferred the
feeder at which they had prior personal experience, despite
conflicting social information. This indicates that they
weighted their personal information more strongly than the
social information that they received during the demonstration. A similar result was reported by Pongrácz et al. (2003), in
which the greater the previous experience of an indirect route
to reach a food reward, the longer it took dogs to adopt
a socially demonstrated shorter route. Thus, in experiment 1
although the social information was sufficient for learning (as
seen with the naı̈ve observers), the reliability of prior personal
experience, together with the low cost associated with
continued use of the personal information, appeared to
insulate these fish against the adoption of the socially
demonstrated alternative food patch.
275
In experiment 2, however, we attempted to increase the cost
of using personal information. The finding that naive control
fish consistently chose the feeder in the open end of the tank
rather than behind the visual barrier confirms the proposed
cost to use of personal information for trained fish. Indeed,
fish in both the trained observer and trained nonobserver
conditions tended to ignore their prior personal information
(directing them to feed behind the visual barrier) but rather
fed at the feeder that their prior personal information
indicated never contained food. The proportions of fish in
the trained conditions entering the feeder to which they had
been trained were virtually identical regardless of the fact that
one condition observed a demonstration of fish feeding at the
alternative feeder and the other did not. It is possible
therefore that fish in the trained observer condition did not
use the social information provided but merely ignored their
prior personal information (as trained nonobservers did)
owing to a shoaling tendency.
At test, trained observers and trained nonobservers spent
an equal amount of time in the zone surrounding the feeder
to which they had been trained. However, we do have
evidence that the trained fish that observed conspecifics
feeding at the previously nonprovisioned feeder did use this
social information. Fish in the trained observer condition
ignored their prior personal information and fed at the
feeder to which they had not been trained more rapidly than
did those fish in the trained nonobserver condition. This
result mirrors that of Pongrácz et al. (2003), who found that
where dogs were prevented from using their prior personal
information to reach a food reward, they used an alternative
route more rapidly when provided with social information as
to its use. It is also consistent with the suggestion of Valone
and Templeton (2002) that public information can be used to
make faster, more accurate choices about the environment.
When the use of personal information was costly, necessitating
loss of visual contact with the shoal, social information was
used, confirming the prediction of Boyd and Richerson’s
(1988) model.
Taken together, the findings of experiments 1 and 2 suggest
that when personal and social information conflict, animals
will be more likely to use social information if the personal
information is costly to use (e.g., necessitating loss of contact
with conspecifics) than if it is not. This result corresponds to
the findings of theoretical analyses regarding the utility of
conformist social learning (Day et al., 2001; Boyd and
Richerson, 1985; Lachlan et al., 1998). However, in contrast
to the Day et al. (2001) study in which the conformity effect
hindered the performance (and subsequent social learning)
of a foraging innovation, in these experiments conformity
promoted social learning. This is because in order to innovate
and socially learn in Day et al.’s (2001) study, guppies were
required to lose visual contact with the shoal, whereas in the
current study it was the use of prior personal information that
required loss of contact with the shoal. This caused fish to
weight the social information more heavily than their prior
personal information, and thus conform. Similarly, in
marmosets a prior personal aversion to a food was overridden
by social information as to its palatability (Queyras et al.,
2000), presumably owing to the cost of unnecessarily avoiding
a nutritious food source.
The present study may shed light on the question as to
whether or not individuals weight personal and social
information equally, as assumed in some recent analyses
(Clark and Mangel, 1984; Templeton and Giraldeau, 1995a,
1996; Valone and Giraldeau, 1993). For example, in studies of
Behavioral Ecology Vol. 15 No. 2
276
the use of public information in mate quality assessment, it
appears that individuals first rely on their own personal
information and only use social information (the mating
decisions of others) when their discrimination ability is
inadequate (Dugatkin, 1996; Dugatkin and Godin, 1993;
Nordell and Valone, 1998). Similarly, in the current study, fish
first relied upon their personal information (experiment 1)
until such a time as the use of this information became too
costly (experiment 2), when social information was used. This
result mirrors that of Templeton and Giraldeau (1996), who
found that starlings only used public information to assess
patch quality when the cost of acquiring accurate personal
sample information increased.
The findings of experiments 1 and 2 are also consistent with
the assumption that, ‘‘the value of public (social) information
may depend upon the cost of acquiring sample (personal)
information’’ (Valone and Templeton, 2002, pp. 21, terms in
parentheses added). Although in this study we did not
manipulate the cost of acquiring personal and social information simultaneously, as suggested by Templeton and
Giraldeau (1995b), we did show that when the cost of
acquiring sample information (to corroborate prior information) was minimal, social information was ignored. However,
when the cost of acquiring sample information increased
(necessitating loss of visual contact with the shoal), social
information was no longer ignored.
Most studies of public information have involved the
comparison of social and personal sample information,
whereas our study involves social and personal prior information. It is thought that the combination of prior
personal and social information is less complicated than the
combination of personal sample and social information
(Valone and Templeton, 2002). It is however, ecologically
feasible that individuals may acquire prior personal and
public information without personal sample information. For
example, subordinate individuals (in a heterospecific or
conspecific scenario) may not have access to defendable
resources to acquire sample information but may have
previously obtained prior personal information and be able
to observe the foraging success of dominant individuals.
However, our study differs from the majority of public
information foraging studies in that we measured the choices
of individuals rather than patch departure decisions. Thus,
the study may be more applicable to instances in which
decisions involve a choice between two options, such as mates,
escape routes, or shelter.
In conclusion, the findings of this study show that positive
frequency-dependent social learning, or conformity, can
promote social learning in naı̈ve individuals, but prior
experience can insulate individuals from conformity provided
the costs of relying on that experience are small. In contrast to
previous assumptions, the current study shows that personal
and social information are not always weighed equally, and
their relative use depends upon the costs involved. The
context-dependent relative weightings of information types
could, and arguably should, be incorporated into foraging
models. Examination of the possibility that conflicting social
information provided by various numbers of individuals
would be weighted differently, relative to personal information, owing to conformity effects could extend the current
study.
We are grateful to J. Kendal and C. Brown for helpful discussion and
to Y. Van Bergen for useful comments on the manuscript. R.L.K. was
supported by a Biotechnology and Biological Sciences Research
Council PhD studentship, I.C. by a Kyssen Foundation Postdoctoral
Fellowship, and K.N.L. by a Royal Society University Research
Fellowship.
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