Larder Hoarding Versus Immediate in situ Food Consumption in Two Fiddler Crab Species: Is it an Evolutionarily Stable...

Larder hoarding behavior in central place foragers has been widely studied in vertebrates, albeit, not as extensively as scatter hoarding. However, scant information is available for the invertebrate taxa, especially aquatic species. We investigated this phenomenon via an in situ food supplementation experiment in a community of two sympatric fiddler crabs, Austruca annulipes (n = 80; 40 males and 40 females) and Gelasimus vocans (n = 60; 30 males and 30 females), in a Singapore mangrove patch with an intermediate resource level. As the semiterrestrial intertidal crabs can only forage after emergence from their burrows during exposure period, the duration of time available for feeding is finite and constitutes an important constraint in the optimization of food intake. The activity budget (in terms of time spent on feeding activities, all above-ground non-feeding activities, and burrow-sequestration) as well as the occurrence (if any) of larder hoarding behavior in these two species after they first emerged were recorded by hourly intervals (three hours of observation) to determine the effect of time left for foraging on larder hoarding. Regardless of species, A. annulipes and G. vocans spent most of the time feeding when the tide was out, despite overall significant behavioral heterogeneity (multivariate analyses using ANOSIM) indicating that both species prioritized hunger satiation over other activities. Our results also showed that although the two sympatric crabs live in the same mangrove area with similar food resource levels, only A. annulipes larder hoarded. The propensity to larder hoard did not differ significantly between the sexes, nor among the three time periods of the feeding duration. Gelasimus vocans, one of the species of crabs known to form feeding droves, did not larder hoard at all. We propose that A. annulipes is a species that can deploy larder hoarding as a foraging strategy when it encounters valuable food resources, and such a strategy is highly advantageous for the species as it generally inhabits sandy habitats that are poor in nutrient levels. Hence, larder hoarding can be considered a mixed evolutionarily stable strategy (ESS) adopted by A. annulipes. In contrast, G. vocans that commonly inhabits muddy sediments-with a high level of food resources-did not larder hoard, even when provided with supplemented food, suggesting perhaps that its mixed ESS is droving behavior.