Foraging group size affects repeatable individual variation and strategic social plasticity

Rori Efrain Wijnhorst , Corné de Groot , Yimen G Araya-Ajoy, Henrik Jensen, Jonathan Wright, Niels J. Dingemanse

Although game theory successfully predicts how negative frequency dependence can maintain behavioural variation through stable equilibria, it does not predict whether this variation reflects repeatable differences among individuals or variation within individuals. Because social group size influences how individuals respond to social information, it may shape how individual variation is distributed around equilibria. Using a producer-scrounger game model, we therefore tested whether group size (three versus six individuals) affects within- and among-individual variation in foraging tactics in wild house sparrows (Passer domesticus). While average scrounging frequency did not change with group size, individuals were less socially responsive and among-individual differences in strategies increased in larger groups. Furthermore, strategies were strongly correlated across treatments, indicating individual consistency in foraging strategies. Non-linear selection analyses revealed negative frequency-dependent selection in small groups, with a locally stable equilibrium (ESS) at a scrounging proportion of 0.332, but no evidence for selection in larger groups. Our findings illustrate that group size can shape within- and among-individual variation in behaviour, thereby altering the individual-level processes through which evolutionary equilibria are maintained. This highlights the need to include continuous among-individual variation and context-dependent social responsiveness in game theoretical models to better predict evolutionary dynamics in natural populations.