portion of the kill supports a large population of bird, 

 mammal, and invertebrate scavengers (Wright 

 1960). Harvestmen are predaceous on insects. Males 

 waste nearly three-fourths of their prey, females 

 about one-third. Of the food ingested, about 46 per 

 cent of the energy is assimilated ; the remainder is 

 eliminated in the feces (Phillipson 1960). 



From measurements made at Lake Beloe, nat- 

 ural mortality of Tendipes plumosiis and other bot- 

 tom fauna is reported to be twice predation (Ricker 

 1946). In a Massachusetts spring-pool, however, 

 non-predatory deaths of another species of midge and 

 of planarians amounted to one-fourth predation (Teal 

 1957). In a small Indiana lake, non-predatory deaths 

 of bluegills amounted to 64 per cent of the average 

 protein content of the standing crop during the year, 

 but only 29 per cent of the total turnover of protein 

 (Gerking 1954). In an Arctic lake not in trophic 

 balance, the net productivity of the entire community, 

 as shown by the accumulation of bottom deposits, 

 averaged something less than 2 mg organic matter/ 

 cm^/yr during the 6000 years since recession of the 

 Pleistocene glacier, compared with 8 mg/cm^/yr in 

 a Connecticut lake during a comparable period of 

 time (Livingstone et al. 1958). 



The food chain or food web thus has a double base, 

 although this useful energy, made available by the 

 transformers, disappears as it recirculates into higher 

 trophic levels. In iDalanced communities it is continu- 

 ously replenished from the producers. Feeders on 

 detritus and transformers are important both in 

 aquatic habitats and in the soil. Mud flats on the Cali- 

 fornia coast contain at least 39 g/m^ dry weight of 

 bacteria. Assuming that this biomass increases only 

 10 times per day, there would be 390 g/m^ produced 

 per day available for nourishment of the animal pop- 

 ulation (ZoBell and Feltham 1942). 



Some of the most intensive and accurate studies 

 of productivity are being carried out with phyto- and 

 zooplankton in marine waters (Riley et al. 1949, 

 Riley 1952, Deevey 1952). It is calculated that the 

 total annual fixation of carbon by photosynthesis in 

 Long Island Sound is about 470 g/m^. Over half of 

 this amount (265 mg) is used in the respiration of 

 phytoplankton (56 per cent). Of the 205 g/m^ net 

 production, 26 per cent appears to be used by the 

 macro-zooplankton. 43 per cent by the micro-zoo- 

 plankton and bacteria, and 31 per cent by the benthic 

 fauna and flora (Riley 1956). In the sea off Plym- 

 outh, England, it has been estimated (Harvey 1950) 

 that the zooplankton is required to assimilate daily an 

 equivalent of 4 per cent of its dry weight in vegetable 

 matter just to meet respiratory needs, and 7-10 per 

 cent for growth and to offset the amount consumed 

 by other animals. Thus, of the energy intake at this 

 level, approximately 30 per cent was used for respira- 



tion and 70 per cent for growth. On the other hand, 

 pelagic fish, at a higher trophic level, used 90 per cent 

 of assimilated food for respiration and converted only 

 10 per cent into body tissue. 



Primary productivity of coral reefs is far greater 

 on an areal basis, 1800^200 grams carbon per square 

 centimeter per year, than for most marine habitats, 

 28-912, but 4650 in an eelgrass bed off Florida. This 

 high productivity is probably due to the luxuriant 

 benthic algae on the reef platforms (Kohn and Hel- 

 frich 1957). 



There are difficulties in obtaining accurate meas- 

 urements of all factors for complete ecosystems. In 

 his pioneer study of lakes, Lindeman (1942), and 

 later also Dineen (1953), found that the percentage 

 of gross energy intake that became transferred 

 through predation to the next higher trophic level 

 became progressively greater (Table 14-1). He also 

 found that the percentage respiratory loss increased 

 at each higher trophic level, and this has been con- 

 firmed for a terrestrial food chain involving plants, 

 mice, and weasels (Golley 1960). 



In a Montana reservoir, of the total gross pro- 

 duction of the phytoplankton during the summer 

 months, 17 per cent was dissipated in respiration, 4.5 

 per cent was converted into increase of phytoplank- 

 ton, 71 per cent was consumed by macro-zooplankton, 

 and 7.6 per cent utilized by bacteria, micro-zooplank- 

 ton, and bottom fauna. The energy intake of the 

 macro-zooplankton was divided 90 per cent for res- 

 piration and 10 per cent for population increase 

 (Wright 1958). Effort should be made to investi- 

 gate these relations more accurately, especially in 

 ecosystems in which all trophic levels are in equi- 

 librium. 



Analyses of energy relations in complete ecosys- 

 tems have been made by Odum and Odum (1955) 

 for a coral reef community in the Pacific Ocean, and 

 Odum (1957) and Teal (1957) for spring-fed 

 streams and pools. These studies of flowing waters 

 are complicated by the export of energy downstream 

 with the current. 



SUCCESSION 



When trophic levels are in balance within 

 an ecosystem, all the net production of one level is 

 consumed by other levels, and there is neither a sur- 

 plus nor a deficit in the total annual production. 

 The biomass of annual plants, the foliage of perennial 

 plants, and the populations of animals with one or 

 more generations per year reach large size at the end 

 of a growing season, far beyond possible immediate 

 consumption by predatious animals at higher trophic 

 levels. Yet this biomass does not accumulate. With 



206 Ecological processes and dynamics 



