Understanding the structure of food webs—the network of prey-predator relationships in ecological communities—is crucial to predict ecosystems' dynamics and stability. Therefore, revealing their structural properties has hence become a central goal in community ecology. There is a growing literature that demonstrates ways in which food webs from different environments exhibit common topological properties. However, these topological properties can often mask more subtle—but no less ecologically important—variation across ecosystems. Here, we propose a new approach to compare ecological networks that overcomes this shortcoming by directly aligning pairs of networks to each other. This alignment between networks provides two levels of information that allow us to investigate the ways different food webs resemble to each other. The first level is an overall measure of how similar the networks are. The second level of information consists on a list of every species-species alignment between networks.
Results/Conclusions
In this study, we used (1) the former measure as a general metric for studying structural differences across ecosystems, and (2) the list of species-species alignments to assess whether or not there is a backbone of interactions underlying all ecological networks. We applied our approach to investigate the topological similarity of a large collection of over 350 food webs from multiple environments and biomes. First, we found significant differences in the way species from different type of ecological communities interact with each other, in contrast to previous suggestions of universality across food webs. This highlights a fundamental heterogeneity across ecosystem types, which could be crucial to explain the way ecological networks adapt to overcome distinct environmental perturbations. Second, and perhaps more surprisingly, we were able to identify a common backbone of interactions underpinning all ecological networks. We expect that this backbone of interactions is important because it might shed light on the possible rules driving the assembly of the different ecological communities. At the same time, this backbone of interactions could also help reconcile the earlier observation of common properties observed across ecosystems while still allowing different networks to differ in fundamental ways.