Density-dependent maturation regulates overcompensation and increases persistence in harvested populations
Induced changes in the demographic traits of harvested populations produce ecological responses to mortality not predicted by traditional models. Maturation rates, in particular, are usually treated as fixed in theoretical and applied models. However, strong plasticity in maturation rates– a phenomenon commonly observed among intensely harvested and invasive species - varies the time between an individual's birth and reproduction, thereby affecting a population’s growth rate. We develop a general model to explore how density-dependent maturation rates affect population persistence and overcompensation ('hydra effect'), a scenario in which control of a nuisance or invasive species through harvest backfires with an increase in total abundance.
Density dependent maturation generally dampens or eliminates overcompensation. However, harvest strategies targeting specific stages of a population can elicit or strengthen an overcompensatory response. On the other hand, maturing at a faster rate when abundance is reduced by harvest allows populations with low juvenile survival to persist under much greater harvest pressures and maintain higher levels of adult abundance. Strong compensatory responses in age at maturity therefore can greatly amplify the harvest effort required to reduce or collapse populations with low survival rates. Accounting for this effect can be critical to invasive species control or eradication, as well as to the conservation of ecologically and/or economically important populations.