Population dynamics-environment interactions and how they relate to stability across scales

Background/Question/Methods

Many metapopulations are only weakly synchronous despite coupling through dispersal and exposure to synchronous environmental drivers. Although this could be due to observation noise, many factors including local environmental differences, spatially variable population dynamics, and chaos could reduce or eliminate metapopulation synchrony, thus promoting overall metapopulation stability. Whether asynchronous population fluctuations are driven by local dynamics or environmental stochasticity has vastly different implications for population management and predicting how populations will respond to environmental change. To differentiate spatially variable dynamics from similar dynamics driven by spatially variable environments, we used hierarchical delay-embedding. A unique output of this approach, the “dynamic correlation,” quantifies similarity in intrinsic dynamics of populations, independently of whether their abundance is correlated (synchronous) through time. We applied these methods to 17 populations of blue crab (Callinectes sapidus) along the U.S. Atlantic coast.

Results/Conclusions

We found that the intrinsic dynamics of blue crab populations were broadly similar despite largely independent fluctuations in abundance. The weight of evidence suggests that the latitudinal gradient in temperature, filtered through a unimodal response curve, is sufficient to decouple crab populations. As unimodal thermal performance is ubiquitous in ectotherms, we suggest that this may be a general explanation for the weak synchrony observed at large distances in many species, although additional studies are needed to test this hypothesis. More broadly, the methodology we present can help us differentiate among mechanisms that decorrelate population trajectories and provide insight into the spatial structure of population dynamics.