Competition avoidance drives individual differences in response to a changing food resource in sticklebacks

Abstract

Within the same population, individuals often differ in how they respond to changes in their environment. A recent series of models predicts that competition in a heterogeneous environment might promote between-individual variation in behavioural plasticity. We tested groups of sticklebacks in patchy foraging environments that differed in the level of competition. We also tested the same individuals across two different social groups and while alone to determine the social environment's influence on behavioural plasticity. In support of model predictions, individuals consistently differed in behavioural plasticity when the presence of conspecifics influenced the potential payoffs of a foraging opportunity. Whether individuals maintained their level of behavioural plasticity when placed in a new social group depended on the environmental heterogeneity. By explicitly testing predictions of recent theoretical models, we provide evidence for the types of ecological conditions under which we would expect, and not expect, variation in behavioural plasticity to be favoured.

Figure 1

Experimental design. 18 individuals were tested in the ‘simultaneous patch’ regime and 18 individuals were tested in the ‘sequential patch’ regime. The three original groups within each regime are represented with different patterns. All individuals were first tested in an original group and then randomly reassigned and tested in a shuffled group. Individuals from the ‘simultaneous patch’ regime were then also tested while alone (see Methods). Each group was tested in 10 trials over 5 days.

Figure 2

Individuals consistently differed in switch delay in the ‘simultaneous patch’ regime (a) and while alone (c), but not the ‘sequential patch’ regime (b). Each line represents a different individual and the panels show different original groups within each regime. The value (95% CI) in the upper right of each panel represents the repeatability estimate for that regime over the entire testing week. When the lines do not cross, there is perfect rank-order consistency over time, for example, between days 4 and 5 in the second panel of (a). One cause of a low estimate of repeatability is when there is little between-individual variation, for example, in (b).

Figure 3

When individuals switched more quickly in the ‘simultaneous patch’ regime they received less food during that trial compared to other trials (a), but when individuals switched more quickly in the ‘sequential patch’ regime (b) and while alone (c) they received more food during that trial compared to other trials. Each dot represents a trial so a single individual is represented by ten dots. The value in the upper right represents the residual covariance between switch delay and food items (95% CI). The regression line is included for illustrative purposes only.

Figure 4

There was significant covariance between individuals’ switch delay across two social groups in the ‘simultaneous patch’ regime, but not in the ‘sequential patch’ regime. Each dot represents one individual and their average behaviour in their original and shuffled group ± 1 SE. The value in the upper right shows the covariance estimate between individual switch delay (95% CI).