How dendritic ecological networks structure the distribution and movement of stream salamanders

Background/Question/Methods Population persistence in a complex network results from the interplay between movement pathways and the configuration of the habitat patches. In dendritic networks such as streams, some animals are restricted to travel along the network (i.e., within the stream), while others may be able to make out-of-network movements (i.e., over land between streams).  Combinations of these movements may be important drivers of metapopulation extinction risk.  Building from a conceptual understanding of some general properties of dendritic ecological networks, I combine results from simulation models and empirical observations of occupancy patterns to forecast the relative importance of the two movement pathways to metapopulation persistence.  To test these predictions, I conducted a mark-recapture experiment to investigate the movement behaviour of one species of stream salamander.  

Results/Conclusions

In the simulation model, I found that out-of-network connectivity has a large effect on the time to extinction in dendritic networks.  This effect was most prominent with high levels of within-network movement, suggesting that out of network movement may not be a primary driver of extinction risk.  Patterns of stream salamander occupancy follow these expectations, and following marked individuals reveals that both within-stream and overland dispersal may indeed result in more robust populations of some species of stream salamanders, even in disconnected networks.  These results suggest that understanding species-specific movement probabilities (and the propensity for out of network movements) are important for assessing metapopulation extinction risk.