Limited effects of size-selective harvesting and harvesting-induced life-history changes on the temporal variability of biomass dynamics in complex food webs

Harvesting has been implicated in destabilizing the abundances of exploited populations. Because selective harvesting often targets large individuals, some studies have proposed that exploited populations often experience demographic shifts toward younger, smaller individuals and become more sensitive to environmental fluctuations. The theory of consumer–resource dynamics has been applied to address the impacts of harvesting in simple modular food webs, but harvested populations are embedded in a complex food web in nature. In addition, exploited populations have been shown to undergo trait evolution or phenotypic changes toward early maturation at smaller sizes. Using an empirically derived complex food web model, Kuparinen et al. (2016. Fishing-induced life-history changes degrade and destabilize harvested ecosystems. Scientific Reports: 6, 22,245) demonstrated that exploited fish populations and other ecosystem properties increased variability due to harvesting and harvesting-induced life-history evolution in the absence of environmental fluctuations. In the present study, we examined a large set of simulated complex food webs to attest the generality of the findings in Kuparinen et al. (2016). We found that harvesting both increased and decreased temporal variability of fish biomass dynamics, especially in food webs with intrinsically oscillating dynamics, while the vast majority of the food webs did not experience destabilization. We also elucidated the large impacts of the shape of functional responses on food web structure, energy flow, and changes in temporal variability caused by harvesting. Our results suggest that the destabilizing or stabilizing effects of harvesting and harvesting-induced evolution importantly depend on the shape of functional responses in dynamical models of complex food webs and that food webs with intrinsically oscillating dynamics are more prone to changes in temporal variability caused by harvesting and harvesting-induced evolution.