‘Stick with your own kind, or hang with the locals?’ Implications of shoaling strategy for tropical reef fish on a range‐expansion frontline

Abstract

Range shifts of tropical marine species to temperate latitudes are predicted to increase as a consequence of climate change. To date, the research focus on climate-mediated range shifts has been predominately dealt with the physiological capacity of tropical species to cope with the thermal challenges imposed by temperate latitudes. Behavioural traits of individuals in the novel temperate environment have not previously been investigated, however, they are also likely to play a key role in determining the establishment success of individual species at the range-expansion forefront. The aim of this study was to investigate the effect of shoaling strategy on the performance of juvenile tropical reef fishes that recruit annually to temperate waters off the south east coast of Australia. Specifically, we compared body-size distributions and the seasonal decline in abundance through time of juvenile tropical fishes that shoaled with native temperate species ('mixed' shoals) to those that shoaled only with conspecifics (as would be the case in their tropical range). We found that shoaling with temperate native species benefitted juvenile tropical reef fishes, with individuals in 'mixed' shoals attaining larger body-sizes over the season than those in 'tropical-only' shoals. This benefit in terms of population body-size distributions was accompanied by greater social cohesion of 'mixed' shoals across the season. Our results highlight the impact that sociality and behavioural plasticity are likely to play in determining the impact on native fish communities of climate-induced range expansion of coral reef fishes.

Predation avoidance and foraging efficiency contribute to mixed‐species shoaling by tropical and temperate fishes

“…In addition to our findings, support for fitness benefits associated with mixed‐species shoaling is provided by Smith et al . (), who found that vagrant A. vaigiensis within mixed‐species shoals displayed increased growth rates relative to those within single‐species shoals.…”

“…Smith et al . () found that A. vaigiensis within mixed‐species shoals had a higher growth rate than those in single‐species shoals. However, they found no differences between the size of mixed‐ and single‐species shoals or between the distance from shelter for A. vaigiensis within each shoal type.…”

“…Smith et al . () reported no significant difference between the size of mixed‐ and single‐species shoals, or the distance from shelter for A. vaigiensis within each shoal type. They therefore attribute increased growth rates of A. vaigiensis within mixed‐species shoals to enhanced social learning in the presence of temperate heterospecifics rather than Allee effects ( i.e.…”

“…Net benefits gained from the formation of mixed‐species shoals can be important in facilitating the growth and survival of displaced gregarious fishes (Camacho‐Cervantes et al ., ; Smith et al ., ). For example, displaced guppies Poecilia reticulata Peters 1859 foraged with the same efficiency when shoaling with native topminnows [ Skiffia bilineata (Bean 1887), Zoogoneticus tequila Webb & Miller 1998 and Xenotoca eiseni (Rutter 1896)] as when shoaling with conspecifics.…”

“…Indeed, mixed‐species shoaling by fishes may afford key benefits to individuals which ultimately increase growth and survival ( e.g. , Camacho‐Cervantes et al ., ; Sackley & Kaufman, ; Smith et al ., ). The net benefits gaind from mixed‐species shoaling theoretically result from multiple fitness trade‐offs predominantly associated with predation risk and foraging efficiency (Paijmans et al ., ).…”