Energy Dynamics of the Grasshopper Populations in Old Field and Alfalfa Field Ecosystems

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Abstract
The bioenergetics of grasshopper populations were studied on a southeastern Michigan old field in 1959 and 1960 and on a first year seeding of alfalfa in 1960. On the old field in 1959 the grasshoppers ingested 4.8 kcal/m2year and assimilated 76 kcal/m2. The population density on the old field in 1960 was lower and total ingestion was only 2.6 kcal/m2 year. Population density on the alfalfa field in 1960 was greater than in either year on the old field and the ingestion by grasshoppers on the alfalfa field was 36 kcal/m2/year. The abundant species were all common to both habitants. Individual growth rates were similar in all three populations and feeding studies indicated that 37% of the energy ingested was assimilated. Production/respiration ratios for the 3 populations ranged from 53-65% and the maximum possible gross yield/ingestion efficiency ranged from 7 for the alfalfa field population to 14.2 for the old field populations in 1960. The peak energy flow of the grasshopper populations occurred late in the summer, when the standing crop of green vegetation was greatest. On the old field, grasshoppers ingested less than 0.5% of the net primary production. Approximately 2.5% of the net primary production on the alfalfa field was ingested by the grasshopper fauna. The high P/R ratios were expected because of the relatively low weight specific metabolic rate of poikilotherms. The relative merits of oxygen consumption vs. feeding studies as measures of respiratory energy loss are briefly discussed. Oxygen consumption measurement was found to have many advantages for some species in given situations.