When animals compete over limited resources, they often assess the value of those resources. This resource value assessment influences contest behavior, including how aggressive competitors are and how quickly they give up the fight. Resource value assessment is usually assumed to be categorical or linear; for example, male-male fights are more aggressive when females are present than absent, or as female fecundity increases. An alternative to these categorical or linear effects is quadratic resource value assessment, in which resource value is highest at a certain level and decreases in either direction. The mantis shrimp Neogonodactylus bredini occupies coral rubble burrows in a size-assortative manner: individuals of a certain body size inhabit burrows of a certain size. Because of this, we hypothesized that mantis shrimp show quadratic resource value assessment during contests over burrows. Using choice trials and staged contests involving mock burrows of various sizes, we tested whether mantis shrimp 1) chose mock burrows predicted to be best fit for their body size, and 2) were more aggressive during, endured higher costs during, and were more likely to win contests over mock burrows predicted to be best fit.
Results/Conclusions
Individuals chose burrows larger than their predicted best fit size. In contests, intruders without burrows were most likely to evict burrow residents when the contested burrow was slightly smaller than the intruder’s predicted best fit size. Intruders’ contest success decreased as burrow size increased or decreased from this value. Intruders won by delivering more strikes and by being aggressive first. In contrast to intruders, burrow residents showed little evidence of resource value assessment. A literature review revealed that quadratic resource value assessment may play a role in contests over diverse resources, from territories to parasite hosts. I discuss future research aimed at understanding links between contest behavior and the distribution of contested resources.
