Processing of Consumed Energy
In the previous two chapters we have discussed the various means by which consumers obtain sufficient rations. In this chapter we focus on the various fates of ingested material and how this apportionment affects consumers. In this section we will look at the overall scheme of flow of ingested material; in the following section we examine the processes that affect the various fates of matter ingested by consumers and some consequences of this partitioning. In many instances the rates of each process vary so widely that it is necessary for comparative purposes to use ratios between two of the processes, which we refer to as efficiencies. After completing the examination of partitioning of food in specific populations, we consider how the partitions are put together in energy budgets for populations and ecosystems.
KeywordsSalt Marsh Energy Budget Sockeye Salmon Growth Efficiency Assimilation Efficiency
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- There has been much research on energy in consumers and many measurements of energy content in terms of calories of biological materials (Paine, 1971; Cummins and Wuychek, 1971). In general, the ash-free caloric content of consumers lies between lower values typical of carbohydrates (3.7 kcal g-1 for glucose, 4.2 kcal g-1 for cellulose) and higher values of lipids and fatty acids (9.4 kcal g-1). Most consumers have a far narrower range of caloric content, averaging about 5–6 kcal g-1 (Holme and McIntyre, 1971).Google Scholar
- See Section 7.323 for definition.Google Scholar
- Net growth efficiency is often labeled “K2” in the literature; “K1” is the gross growth efficiency, equal to (G/C) 100.Google Scholar
- An extreme of this tendency is the “feeding frenzy” that takes over many predators when exposed to a very dense aggregation of prey.Google Scholar
- One exception to this is that measurement of O2 consumption or CO2 production can provide assessment of respiration by the assemblage of consumer populations present. This approach has been used to measure “community respiration” in marine benthic communities, as will be seen in Chapter 10.Google Scholar
- The production-size relationship is good enough to have encouraged Sheldon and Kerr (1976), based on the dimensions and food availability in Loch Ness, plus more speculative guesses as to size, to predict that there may be 10–20 monsters present in the Loch, assuming they are top predators.Google Scholar
- The units generally used are calories. The content of 1 g of phytoplankton carbon is about 15.8 kcal, 1 g of dry weight phytoplankton is about 5.3 kcal. Consumption of 1 ml of O2 by an animal provides about 3.4–5 cal; taking the latter value, and an R.Q. of 1, 1 mg of dry food is about 5.5 cal. Energy content is also expressed in joules (J), and 1 cal = 4.19 J.Google Scholar
- There are some other estimates of the relative activity of macro- and meiofauna. In a tidal mudflat in the Wadden Sea, macrofauna biomass is 20 times that of the sum of meiofauna, microfauna, and bacteria (Kuipers et al., 1981). Yet, since the metabolic rate of a nematode, for example, is about 21 times higher than that of an average macrobenthic specimen, 74% of the organic matter is consumed by the small organisms. In other soft-bottom marine habitats respiration of the macrofauna ranges from 2 to 34% of the total respiration of the community (Pamatmat, 1968; 1977; Banse et al., 1971; Smith et al., 1972; Smith, 1973; Davies, 1975).Google Scholar
- Ryther calculated that 20 × 109 tons of carbon were produced per year in the sea by primary producers. This is lower than more recent estimates of 31 × 109 tons of carbon year-1 by Platt and Subba Rao (1975). Ryther also did not consider the microbial pathways of energy flow that have received recent attention. It is not clear if these omissions cancel each other; Ryther’s estimates should therefore be taken as just that: estimates.Google Scholar