Fig. 1: Visual representation of a network of co-occurrence and the corresponding network of biotic interactions and their degree distribution.

a, A co-occurrence network is built based on empirical observations of presence and absence of each species in each spatial unit of each dataset. An interaction is added to the network of co-occurrences when two species from different trophic levels (for example, plant–pollinator or host–parasitoid) co-occur in at least one spatial unit. For instance, a pollinator will have as many interactions in the network of co-occurrences as plants found co-occurring with it in the spatial units analysed. Notice that the frequency of co-occurrence (that is, the number of times two species co-occur across spatial units) varies across species. Species coloured in orange have a higher frequency of co-occurrence. The network of biotic interactions is based on empirical observations of the interactions between species in each spatial unit. Thus, an interaction between two species is added to the network of biotic interactions if it was empirically observed in at least one spatial unit. b, Once both types of networks are built, we can analyse their fundamental characteristics. One of them is network degree distribution, which represents the cumulative probability of finding a species in the network with at least a given number of interactions. Therefore, the probability of finding a species in the network that has at least one interaction with another species is 1. The shape of the network degree distribution indicates how links are distributed among species in the network. For instance, an exponential shape indicates that the occurrence of a link in the network is independent of the presence of other links, while power-law distributions indicate that links are more likely to occur among species that already have more links (that is, the rich-gets-richer phenomenon).