| dc.description.abstract | The dynamics of wild populations are affected by density dependent and density independent processes that vary across multiple temporal and spatial scales. Despite this high complexity, populations often show some degree of spatial synchrony. This means that the dynamics of populations separated in space are correlated to some degree depending on the distance that separates them, where the dynamics of nearby populations are more similar than the dynamics of distant populations. Understanding this phenomenon is crucial because it influences ecological processes related to the invasiveness of species, vulnerability to disease spread, effectiveness of conservation areas, maximum sustainable yield and even extinction probability. Three processes are known to drive spatial synchrony.
Populations affected by a density regulating environmental factor can be synchronized across large areas if the same environmental factor is synchronized across large areas.
Dispersal of individuals can homogenize their density across space synchronizing the population.
Species interactions can also have synchronizing effects when, for example, a nomadic predator regulates the population dynamics of a prey species over a large area.
However, species interactions can also have spatially desynchronizing effects depending on factors such as the type of interactions, the relative dispersal rate of each species or the number of trophic levels in the system. We therefore need good modelling techniques to accurately predict and understand population dynamics in multispecies systems, in order to accurately assess the effects of species interactions on spatial synchrony.
In my PhD thesis, I studied several processes expected to affect spatial synchrony and found that:
Spatial synchrony in population density is influenced by the pace of life history of a species, where species characterized by lower growth, mortality, and fecundity rates (i.e., slow lived species) tend to by spatially synchronized over larger extents than species characterized by high growth, mortality, and fecundity rates (i.e., fast lived species).
Spatial synchrony can vary between the age classes of a population, however, among the three species that we studied, synchrony was found to increase with age in cod, decrease with age in beaked redfish and not change with age in haddock. My result suggests that changes to the age structure of a population could influence its degree of spatial synchrony.
In the Barents Sea, temperature was found to have a synchronizing effect on the fish populations, and density dependence had a desynchronizing effect. These effects were consistent across species, although they were weak, indicating that other processes play a larger role.
Lastly, I reviewed the development of methods to study multispecies population dynamics across fields of ecological modelling to identify challenges, limitations and promising paths forward. Estimating species interactions, dealing with modelling complexity, and accounting for uncertainty were the most pressing challenges across approaches. I discussed some of the strategies taken in different studies to overcome some challenges, and highlight the promise of combining approaches with contrasting strengths and weaknesses to best model multispecies dynamics. | en_US |
