Food-dependent growth leads to overcompensation in stage- specific biomass when mortality increases: the influence of maturation versus reproduction regulation

We analyze a stage-structured biomass model for sizestructured
consumer-resource interactions. Maturation of juvenile
consumers is modeled with a food-dependent function that consistently
translates individual-level assumptions about growth in body
size to the population level. Furthermore, the model accounts for
stage-specific differences in resource use and mortality between juvenile
and adult consumers. Without such differences, the model
reduces to the Yodzis and Innes (1992) bioenergetics model, for which
we show that model equilibria are characterized by a symmetry property
that reproduction and maturation are equally limited by food
density. As a consequence, biomass production rate exactly equals
loss rate through maintenance and mortality in each consumer stage.
Stage-specific differences break up this symmetry and turn specific
stages into net producers and others into net losers of biomass. As
a consequence, the population in equilibrium can be regulated in
two distinct ways: either through total population reproduction or
through total population maturation as limiting process. In the case
of reproduction regulation, increases in mortality may lead to an
increase of juvenile biomass. In the case of maturation regulation,
increases in mortality may increase adult biomass. This overcompensation
in biomass occurs with increases in both stage-independent
and stage-specific mortality, even when the latter targets the stage
exhibiting overcompensation.