Mass and quality-quantity trade-off

The net energy that is available for self-replication generates a quality-quantity trade-off where a parent can produce many small or a few large offspring. And with fitness being given by the exponential increase in numbers on a per generation timescale, r = ln λ ∝ ln [p ε τ / w], this generates a physiological background selection for the absence of mass, with the partial selection gradient on mass on logarithmic scale being minus one

∂ r / ∂ ln w = - 1

[λ:per generation multiplication factor; p:probability to survive to reproduce; τ:reproductive period; w:body mass].

The natural selection of organisms with anything but an absolute minimum mass is therefore, in one way or the other, dependent upon mechanisms that will make the intra-specific dependence of net energy on mass increase stronger than linearly with mass.

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