Unravelling mechanisms behind population dynamics, biological traits and latitudinal distribution in two benthic ecosystem engineers: A modelling approach

The mechanistic approach consisting of coupling Dynamic Energy Budget (DEB) models to Individual-BasedModels (IBMs) allows simulating individual and population biological traits and their dynamics. This approachwas developed here to study population dynamics of two sympatric intertidal ecosystem engineers, Arenicolamarina and Arenicola defodiens (Annelida Polychaeta) occurring in the North-East Atlantic from Portugal toSweden. Latitudinal heterogeneity of the two species’ performances were investigated in terms of populationdynamics and biological traits using latitudinal differences in environmental forcing variables. The impactof the forcing variables on population dynamics processes (shore colonisation and migration, spawning andrecruitment, etc.) within a specific foreshore (mean values and seasonal patterns) was also assessed. PublishedDEB parameters were used for A. marina and a specific calibration was undertaken for A. defodiens, combiningliterature data and new laboratory experiments and field data. Our DEB-IBM simulated super-individuals’growth and reproduction while lugworms were colonising, migrating and dying over a simulated foreshore.Density rules affected population dynamics. Environmental forcings consisted in monthly values of chlorophylla(chl-a) concentrations and daily values of SST. Scenarios focusing on the two most contrasted of theseforcing variables time series were used to explore their relative effects over populations’ dynamics and onshoreprocesses were investigated at two sites displaying highly different simulated population abundances.Overall, northern sites with higher chl-a levels performed better displaying higher biomass, maximum lengthand reproductive outputs for both species. As expected, Sea Surface Temperature (SST) changes between sitesdid not impact greatly populations dynamics. Under favourable environmental conditions, intra- and interspecificcompetitions emerged from the model. Under non-favourable environmental conditions, A. defodiens’populations crashed and A. ...