The development of encompassing general models of ecology is precluded by underrepresentation of certain taxa and systems. Models predicting context‐dependent outcomes of biotic interactions have been tested using plants and bacteria, but their applicability to higher taxa is largely unknown. We examined context dependency in a reproductive mutualism between two stream fish species: mound nest‐building bluehead chub In a large‐scale in situ experiment, we manipulated egg predator density and presence of both symbionts (biotic context), and replicated the experiment in habitats containing high‐ and low‐quality spawning substrate (abiotic context). Contradictory to our first hypothesis, we observed that The results of this study yielded novel insight into how context dependency operates in vertebrate mutualisms. Although the dilution effect provided by
Prey species often congregate in groups to detect and evade predators, yet not all group members benefit equally. We observed the nesting aggregations of bluehead chub ( Vigilance was measured as the time it took the host (male) chub, first chub female and first individual of each associate species to return to the nest under differing associate abundances (hypothesised to be inversely related to risk) following a simulated predator scare. Spatial position was investigated by digitising host movement and overlaying it with the aggregation and nest's spawning pit area. We used information theoretic statistics to analyse the effect of aggregation characteristics on the return time of chub and their nest associates. The best‐supported model included both species composition and abundance (inverse of risk) as predictors of return time. Hosts returned last under nearly all scenarios and the aggregation as a whole took longest to return in high‐risk environments. The 95% and 99% confidence ellipses of host spatial position contained the centroids of the aggregation and spawning pits, respectively, for all nests analysed ( We conclude that the host locates itself at the centre of both the aggregation and the spawning pit area of the nest, and that the host uses the aggregation to reduce its own vigilance requirements. These results support our hypothesis that hosts use their nest associates to disproportionately decrease their risk of predation during spawning. This is the first study to show any mixed‐species fish spawning aggregation as a selfish shoal, and to identify bluehead chub as a selfish participant in the mutualistic reproductive interactions that they host.
- NSF-PAR ID:
- 10491024
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Freshwater Biology
- Volume:
- 69
- Issue:
- 3
- ISSN:
- 0046-5070
- Format(s):
- Medium: X Size: p. 450-459
- Size(s):
- ["p. 450-459"]
- Sponsoring Org:
- National Science Foundation
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