20 30

Age (years)

FIGURE 9.10 Average growth profiles for male and female sperm whales (Physeter macro-cephalus) whose ages were determined by counting the annual layers in their teeth. Marked sexual dimorphism in growth rates and maximum sizes of this squid-eating toothed whale species (Fig. 9.6) reflects their different energy partitioning for growth and reproduction (Fig. 9.8). Modified from Brown and Lockyer (1984).


(activity + basal metabolism)


(growth + reproduction)



FIGURE 9.8 Generalized illustration of food energy that is consumed and partitioned by an organism for life-sustaining activities associated with its basic maintenance and production. Basic maintenance includes metabolic activities associated with respiration, digestion, and excretion, as well as any movement activities for obtaining the food. Food that is excreted and not assimilated for basic maintenance or production is unutilized waste. Production involves food energy that is converted into biomass through both growth and reproduction.

Based on the ecological efficiency (E, which varies from 0 to 1) and the biomass of the primary producers (B), the production (P) at any trophic level (n) then can be calculated:

Figure 9.7 illustrates the application of Eq. (9.3) with an average ecological efficiency of 0.1, which indicates that 10% of the food energy is transferred into biomass at the next higher trophic level.

As reflected by species' growth rates, however, the amount of biomass produced within a population is variable. For example, the finely spaced shell bands of Antarctic scallops (Adamussium colbecki) provide detailed evidence about their growth (Fig. 9.9). Not only does scallop growth fluctuate on a seasonal cycle (as indicated by the pattern of relatively wide and narrow shell rings, like growth rings in trees), but their growth markedly decreases after the scallops reach sexual maturity. In fact, decadal mark-and-recapture experiments with the Antarctic scallop indicate that this benthic species grows less than a millimeter per year during adulthood—reaching sizes larger than 100 millimeters only after more than a century (Plates 5 and 6). Moreover, as illustrated by the sperm whale, there also can be differences between the growth of males and females because of their distinct energy requirements for reproduction (Fig. 9.10). Together, these growth patterns

0 0

Post a comment