Foraging Ecology of the Striped Swamp Snake, Regina alleni, in Southern Florida

The foraging ecology and trophic dynamics of the striped swamp snake, Regina alleni, were studied from 1974—1977 in a south Florida water hyacinth community. The mean standing crop of R. alleni was 30.79 kg (1289 individuals)/ha of water hyacinths. This biomass estimate is greater than that known for any snake species and is related to (1) the high primary productivity of water hyacinths; (2) the trophic positions, diets, and concomitant abundances of the snake's prey; (3) the availability of alternate habitats for exploitation; and (4) release from certain competitive and predatory pressures. Snake density was lowest in summer, increased in fall and winter, then decreased in spring. Changes in density apparently represent seasonal movements of snakes between the hyacinth habitat and the surrounding marshes, in response to fluctuations in water level, prey availability, and predator pressure. R. alleni showed dramatic seasonal and ontogenetic shifts in food habits. Young R. alleni (120—200 mm snout—vent length [SVL]) fed primarily on libellulid odonate naiads but switched to seasonally abundant palaemonid shrimp and astacid crayfish. Between 200 and 300 mm SVL a major dietary shift occurred and crayfish gradually replaced odonates and shrimp. This change occurs throughout the range of the species and also involves a reorganization of snake feeding behavior to accommodate prey of different shapes. The ecological and energetic consequences of this dietary shift are interpreted in terms of the divergent life histories and growth patterns of the predator and its prey. Within the specialized trophic niche of R. alleni, food availability and predator size largely determined the types and sizes of prey consumed, but interacted with the thermal regime, energetic requirements, and foraging efficiencies of individual snakes to determine the rate of food intake. In most seasons juvenile R. alleni consumed more but smaller prey than adults, and the mean percent of snake body mass eaten per day was higher for adults. However, because juveniles fed on odanate naiads that were higher in protein but lower in ash content than the decapods taken by adults, the energetic intake per gram snake body mass was generally higher in juveniles. The predatory impact of R. alleni may be a significant factor limiting the growth of both the snake and its prey populations. During fall, when measured rates of food intake were highest, adult R. alleni consumed °9.6% of the adult crayfish population. In contrast, juveniles accounted for removal of °90.7% of the odonate population in the same time period. When given an unlimited food supply in the laboratory, the daily energetic intake of juveniles was more than two times that of maximum field estimates.