Towards an ultimate explanation for mixed‐species shoaling

• Published in: Fish and fisheries (Oxford, England) England), 2019-09, Vol.20 (5), p.921-933
• Main Authors: Paijmans, Kai C., Booth, David J., Wong, Marian Y. L.
• Format: Article
• Language: English
• Subjects: Animal species; Ecosystems; fish; Fitness; fitness trade‐off; Foraging; Foraging behavior; Frameworks; Freshwater; Freshwater ecosystems; group living; Group size; heterospecific; Inland water environment; Interspecific relationships; Literature reviews; Marine ecosystems; Predation; Predators; school; Shoaling; Shoals; Social behavior; social groups; Species; Vigilance
• ISSN: 1467-2960; 1467-2979
• DOI: 10.1111/faf.12384

The formation of social groups has important impacts on fitness for many animal species, with differences in group compositions resulting in a range of fitness outcomes for individuals. Recent interest in mixed‐species grouping, which extends from a large body of literature invested in understanding single‐species grouping, highlights novel complexities of group formation which relate to phenotypic, behavioural and physiological differences that naturally exist between species. Among fishes, mixed‐species shoaling is a common form of social grouping behaviour displayed across a range of marine and freshwater ecosystems. Research explaining mixed‐species shoaling shows some overlap with explanations for single‐species shoaling; however, it also demonstrates that distinct differences between species give rise to unique cost‐benefit trade‐offs which need to be incorporated into conceptual models of mixed‐species shoaling behaviour. Unique predation related trade‐offs may arise from inefficiency of the confusion effect, variation in vigilance between species and unequal species‐preferences shown by predators, whilst unique foraging‐related trade‐offs may arise from diet partitioning, variations in foraging behaviour and differences in competitive abilities between species. We review the literature on fitness outcomes associated with mixed‐species shoaling and present a new theoretical framework to explain the cost‐benefit trade‐offs for individuals within mixed‐species shoals. The framework incorporates both trade‐offs arising from differences between species and those arising from group size, the former having been largely ignored due to a focus on single‐species shoaling. Our framework is designed to inform future research striving to explain mixed‐species shoaling behaviour.