Does the presence of an odd individual affect group choice?

Data collected by FQ. Please refer to the manuscript
for data collection methods and statistical analyses. Metadata for the .csv
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This table contains the data recorded during an experiment
to examine how the presence of an ‘odd’ individual in a shoal affects the
behaviour and group choice of three species of coral reef fishes.

ABSTRACT:

Intra-specific group formation (shoaling) is common
in fishes and provides several antipredator benefits, such as improved food and
predator detection. However, coral reef fishes often form mixed-species shoals,
which can generate costs for some group members. For example, the oddity effect
posits that individuals that stand out from a group are more likely to be
targeted by predators. Consequently, the presence of an odd fish might reduce
the risk of predation to other group members. Alternatively, an odd individual that
attracts predators might increase predation risk for the group as a whole. We examined
three species of coral reef fishes using two-choice tests to investigate 1) whether
individuals chose to associate with conspecifics over heterospecifics (i.e. the
oddity effect), and 2) whether individuals associate with or avoid shoals
containing an odd individual. We tested this second scenario under conditions
of low- and high-predation pressure by manipulating the presence of a nearby
predator. One species actively avoided associating with shoals of heterospecifics
in support of the oddity effect. Less pronounced phenotypic differences between
species pairs likely resulted in a lower relative risk of being odd and the
absence of an oddity effects in the other two species. None of the three
species showed either active avoidance or preference for shoals containing an
odd individual. In instances where the oddity effect is apparent, lower
predation risk to individuals associating with an odd fish might be negated by greater
predation pressure on the group as a whole