Understanding the processes that drive population dynamics in river systems can inform better management and conservation. The dendritic geometry of rivers can impact ecological processes such as movement of organisms, which may result in different population distributions compared to other types of habitat networks. Previous studies consider the effects of spatial structure of river networks on population distributions (regional effects), while local effects of dendritic river networks have been less researched. In this study, we investigated how the positions of local areas (sites/ nodes) within river networks affect population densities. We predicted that more central nodes would have larger populations and tested an underlying assumption that different arrangements of topologically equivalent networks will have the same effect on population distribution. This is preliminary research within a larger PhD project that examines the effects of dendritic network structure on population dynamics in laboratory settings.
We conducted experiments with artificial river networks populated with Daphnia carinata, an easily cultured species. Networks consist of individual nodes (bottles) connected by clear tubing through which organisms can travel. Two sets of networks are built. One group is straight lines. The other group has altered edges direction which makes them form “S” shapes.
Results showed that the topologically equivalent networks had the same effect despite their different physical arrangements. However, it took a longer time for the networks with smaller radius (distance from the centre to the edge of the network) to reach the same population distribution as networks with larger radius. Nodes (bottles) located centrally had higher population densities.
Results imply that the position within the network can have an impact on local population densities, potentially affecting population distributions at larger scales. Implications for the ecology and management of river systems are discussed, as well as how these results feed into the ongoing PhD research.