2021

Ahti, Pauliina A.

Aquatic ecosystems are going through an unprecedented decline in biodiversity. This is clearly reflected in the phenomenal declines in fisheries catches and collapses of many fish populations. Different levels of biological organisation interact in complex ways, and changes in fish life-history traits are reflected at population and ecosystem levels. However, the mechanisms behind those interactions are not well understood, and some interactions are completely unknown. This work uses mathematical modelling to explore how senescence, an often-ignored life-history trait affects fish population dynamics and response to fishing. Simulations demonstrate that senescence leads to evolutionary trajectory towards declining asymptotic length and population response to different fishing selection regimes depends on the presence of senescence. The link from population dynamics to life-history evolution is explored through population oscillations. Mathematical simulations show that oscillation wavelength shorter than the maximum lifespan of the fish produce marked differences in the evolution of asymptotic length. Wavelengths longer than the maximum lifespan in turn manifest in ecological effects seen as biomass fluctuations. The combination of the length and amplitude of the oscillation wave determine the direction of the change. Finally, the link between a single species and ecosystem is explored by introducing an invasive species in a food web model. The invasive species sets off a bottom-up effect seen in the decline of biomass. This effect propagates through all trophic levels in the model, including top predator fishes. These findings illuminate some previously unknown or poorly understood links between different levels of biological organisation that will help us better manage and conserve the aquatic nature.