The influence of food deprivation and food availability on feeding in UCA pugilator (BOSC)
The sand fiddler crab, Uca pugilator (Bosc), is a semiterrestrial burrowing crab which lives in intertidal areas along the Eastern and Gulf coasts of the United States. Like other fiddler crabs, U. Pugilator feeds by sorting soil particles with its mouthparts. Unlike most other fiddler crab species, however, U. Pugilator lives in an exposed, barren habitat characterized by sandy soils; these soils provide a relatively impoverished food source for this species.
The basic intent of this study was to determine the effect of food deprivation and food availability on various subcomponents of the overall feeding behavior of U. Pugilator. These subcomponents, which served as categories for data collection, included: (1) feeding rates, measured as the total number of feeding motions made by a crab's feeding claw(s) per minute; (2) lengths of feeding periods, estimated by the ratio of feeding to nonfeeding crabs throughout a daily activity period; and (3) distances traveled during feeding periods, measured as the absolute or relative distance from a feeding crab to its burrow. Data were collected for each of these behavioral categories by direct observation of individual sand fiddler crabs subjected to varying periods of food deprivation; observations were likewise made on individual crabs in areas whose substrates had been enriched, to various degrees, by the addition of food.
Food resource distribution in the habitat of U. Pugilator was determined by quantitative organic carbon analysis of soil samples. Field extraction efficiencies for this species were estimated by comparing the organic carbon levels of foraged and unforaged substrate. Laboratory experiments of the sand fiddler's feeding behavior investigated the crab's ability to detect food levels in the substrate, and examined the influence of sexual dimorphism on feeding behavior.
Results of this study indicate that both food deprivation and substrate food availability may affect the length of feeding periods, as well as distances traveled during feeding periods. The length of time that crabs feed, and their location during the feeding process, may in turn greatly influence the crabs' risks of predation, dessication, and hyperthermia. Neither food deprivation nor substrate food availability appears to affect feeding rates, however. Males fed at approximately 2/3 the rate of females in all experiments in this study, indicating that intersexual differences in feeding rates are probably a result of sexual dimorphism in this species.
Uca pugilator can apparently detect small differences in the food levels of adjacent substrates, and can change its feeding behavior in response to perceived food levels. The feeding activities of this species result in a significant short-term decrease in the organic carbon levels of the foraged substrate, but the long-term effect of its feeding and burrowing activities may be an increase in food availability in some areas. Thus, U. Pugilator modifies its feeding behavior according to gradients of food density in its habitat, and through its foraging and burrowing activities may actually create new gradients in food density.
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