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 and may result in different population outcomes compared to other habitat networks types. We investigated how the positions of local areas (sites/nodes) within river networks affect population densities. We predict 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 part of a larger project examining the effects of dendritic network structure on population dynamics in laboratory settings, which is considering population size, distribution, and resilience/resistance to disturbances.
We conducted experiments with artificial river networks populated with Daphnia carinata, which we are using as a model species in our research. Networks consist of individual habitat nodes (jars) connected by clear tubing through which organisms can travel (edges). This modular system means that networks with different complexities can be built.
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 a smaller radius (distance from the centre to the edge of the network) to reach the same population distribution as networks with a larger radius. As predicted, nodes 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. Similar experimental settings may be applied in community ecology studies. Implications for the ecology and management of river systems are discussed, as well as how these results feed into the ongoing PhD research.