Habitat patches may be distributed across landscapes and connected by dispersal pathways, creating habitat networks at landscape scales. Habitat network structure can vary in complexity, depending on the spatial arrangement of habitat patches and the topology of dispersal pathways. Theory predicts that changes in these elements of network structure will affect population outcomes (network carrying capacity, population distribution and temporal variation), but few empirical field studies have been conducted due to logistical difficulties.
We conducted laboratory experiments to explore the effect of habitat network topology on population outcomes of a model species. Populations of Daphnia carinata were maintained in artificial habitat networks of three types (linear, dendritic, lattice) and six topologies, which differed in the position of nodes (habitat patches) and connection pathways. Over three months populations were censused for growth and stationary phases.
In lattice networks at the node scale, we observed a strong effect of node position on the temporal variability of population size. Node-scale populations located more centrally within networks were more temporally stable. At the network scale, carrying capacity was weakly positively, but not significantly, correlated with network complexity. Spatial distribution of Daphnia among nodes was not significantly different among network types or topologies.
Our observation that temporal variation in node-scale population sizes differs among positions within networks is new; a previous focus on community composition in laboratory experiments has overlooked temporal variability of populations. However, the result is consistent with theory and field observations suggesting that central patches support more stable populations. The results imply that central patches could be of higher priority for conservation. Empirical research under more field-realistic conditions would be useful for testing the generality of our results, but our work demonstrates the value of laboratory studies as a step to bridge this gap.