and (3) Orchelimum fidicinium , a grasshopper. Net production of 

 Spartina was determined by a periodic harvesting of the grass and 

 calculation of the between-sample increase. Animal production was 

 found by periodic harvesting and calculation of population biomass 

 accumulation and biomass lost through mortality. Caloric equivalents 

 of the three components were determined by combustion in a bomb calorim- 

 eter. Respiratory rates of the two animal species were determined 

 over the size range of the animals and the temperature range which 

 occurred in the marsh; total respiration of the population, as found 

 by sampling in the marsh, was then found on an annual basis. The 

 respiratory rates were converted to calories by Ivlev's oxycaloric 

 coefficient, or a modification thereof. Ingestion in grasshoppers 

 was determined by weighing feces under controlled conditions and then 

 adding respiration and production. Ingestion for Littorina was found 

 with the aid of a production/defecation ratio for Littorina obtained 

 from the literature. From these data, production, assimilation and 

 ingestion of the animals and net production of Spartina were compared on 

 an annual basis. 



Production and assimilation (which is equivalent to energy flow) 

 follow a similar pattern in both snails and grasshoppers, but population 

 density is a very poor indication of the actual biomass or energy flow 

 of the populations. The snails were found to be present in two 

 distinct population segments: a large-snail population of high 

 mortality and constantly changing size due to variable recruitment and 

 growth. The biomass of the large snails was so much greater than 

 that of the small snails that, in spite of the greater respiratory 

 rate per unit weight of the small snails, their net environmental 

 significance was minor compared with the large snails. 



The annual cycle of energy flow of the grasshoppers corresponded well 

 with their only food source, Spartina , being high in the early summer 

 and dwindling to zero by September. The energy flow of the snails 

 was more constant, showing only a slight mid-summer peak caused by 

 higher summer respiratory rates. The more constant rate of the snail's 

 energy flow was in good agreement with the constant supply of detritus 

 in the marsh and surrounding waters, from which the snails derive 

 their food. 



Utilization efficiency of Orchelimum (ingestion/net production of 

 Spartina ) was about 2 percent, indicating that the grasshoppers were in 

 an environment which contained an abundant food supply. Assimilation/ 

 ingestion (based on populations over a year) was 36 percent for 

 Orchelimum and 45 percent for Littorina ; production/assimilation was 

 37 percent for Orchelimum and 14 percent for Littorina . It is suggested 

 that the grasshoppers sacrifice efficiency of food concentration for 

 a higher production rate, while Littorina , living in a food-poor 

 environment, must expend a relatively large amount of effort in food- 



260 



