. Elements of ecology. Ecology. 484 Dynamics of the Ecosystem high equihbrium level for the standing crop. In the second situation the growth of the population is much slower, but the same ultimate size of standing crop is attained. In the third situation the same period of time is required to reach equilibrium as in the second, but a lower equilibrium level is established. If a census of the standing crop is taken before the populations have reached their maximum equilibrium levels, the larger standing crop will clearly occur in the area in which the rate of production has been the greatest.
. Elements of ecology. Ecology. 484 Dynamics of the Ecosystem high equihbrium level for the standing crop. In the second situation the growth of the population is much slower, but the same ultimate size of standing crop is attained. In the third situation the same period of time is required to reach equilibrium as in the second, but a lower equilibrium level is established. If a census of the standing crop is taken before the populations have reached their maximum equilibrium levels, the larger standing crop will clearly occur in the area in which the rate of production has been the greatest. Usually, Equilibrium standing crop. Short season Long season Time Fig. Relation between size of standing crop and rate of growth of popula- tion. (Clarke, 1946.) however, the observer will enter a natural area long after the initial growth of the population has been completed and will measure the standing crop at or near its equilibrium level. At this point the magnitude of the standing crop is not an index of growth rate. The size of the population at any moment is the result of the accumulation of production minus the amount of destruction which has taken place up to the time of observation. In the initial growth of the population the length of life of the indi- viduals influences the steepness of the population curve because, the longer each individual lives, the faster will the total numbers increase. Once equilibrium has been reached, however, individual length of life has no effect upon the size of the standing crop. As discussed in Chapter 9, natality is equal to mortality at equilibrium, or A = M. If 50 animals are born per unit of time, 50 animals will die in the same period, and it makes no difference whether those animals have lived 5 days or 5 years. Similarly, the size of the population is not de- termined by the magnitudes of A and M. As indicated in the dia- gram, a population with a large standing crop may exhibit a low. Please note that these images are e
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