Abstract
Classical models of population dynamics do not account explicitly for individual growth and development, despite the fact that most if not all species exhibit significant development and growth in body size during life history. Just like reproduction, growth and development often depend on food density. Models that do account for both food-dependent reproduction and development predict that a population in equilibrium may be regulated in two distinct ways: either through total population reproduction as limiting process or through total population maturation. I will show that in case of reproduction regulation any increase in mortality may actually lead to an increase in juvenile biomass. Similarly, in case of maturation regulation increases in mortality may increase adult biomass. This overcompensation in biomass occurs with increases in both random and stage-specific mortality, even when the latter targets the stage exhibiting overcompensation. When occurring in prey species biomass overcompensation may have important community consequences. In particular, in combination with size-selective predation it may lead to emergent Allee effects for stage-specific predator populations and catastrophic collapses of communities, as well as to facilitation between stage-specific predators that exploit different stages of prey. These theoretical predictions explain the outcome of some classical harvesting experiments with blowflies and waterfleas, as well as the lack of recovery of Atlantic cod populations after their collapse through over-exploitation. In addition, they suggest innovative strategies for population recovery, the effectiveness of which are confirmed by a recent manipulation of the fish community in a large Norwegian lake.
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The CEES seminar room has a coffee-machine – it is therefore recommended that you come a bit earlier and get yourself a good cup of coffee (for the price of 3 NOK).