The presence of territorial damselfish predicts choosy client species richness at cleaning stations

Mutualisms are driven by partners deciding to interact with one another to
gain specific services or rewards. As predicted by biological market
theory, partners should be selected based on the likelihood, quality,
reward level, and or services each partner can offer. Third-party species
that are not directly involved in the interaction, however, may indirectly
affect the occurrence and or quality of the services provided, thereby
affecting which partners are selected or avoided. We investigated how
different clients of the sharknose goby (Elacatinus evelynae) cleaner fish
were distributed across cleaning stations, and asked what characteristics,
relating to biological market theory, affected this distribution. Through
quantifying the visitation and cleaning patterns of client fish that can
choose which cleaning station(s) to visit, we found that the relative
species richness of visiting clients at stations was negatively associated
with the presence of disruptive territorial damselfish at the station. Our
study highlights, therefore, the need to consider the indirect effects of
third-party species and their interactions (e.g. agonistic interactions)
when attempting to understand mutualistic interactions between species.
Moreover, we highlight how cooperative interactions may be indirectly
governed by external partners.