Data from: What can interaction webs tell us about species roles?

The group model is a useful tool to understand broad-scale patterns of
interaction in a network, but it has previously been limited in use to
food webs, which contain only predator-prey interactions. Natural
populations interact with each other in a variety of ways and, although
most published ecological networks only include information about a single
interaction type (e.g., feeding, pollination), ecologists are beginning to
consider networks which combine multiple interaction types. Here we extend
the group model to signed directed networks such as ecological interaction
webs. As a specific application of this method, we examine the effects of
including or excluding specific interaction types on our understanding of
species roles in ecological networks. We consider all three currently
available interaction webs, two of which are extended plant-mutualist
networks with herbivores and parasitoids added, and one of which is an
extended intertidal food web with interactions of all possible sign
structures (+/+, -/0, etc.). Species in the extended food web grouped
similarly with all interactions, only trophic links, and only nontrophic
links. However, removing mutualism or herbivory had a much larger effect
in the extended plant-pollinator webs. Species removal even affected
groups that were not directly connected to those that were removed, as we
found by excluding a small number of parasitoids. These results suggest
that including additional species in the network provides far more
information than additional interactions for this aspect of network
structure. Our methods provide a useful framework for simplifying networks
to their essential structure, allowing us to identify generalities in
network structure and better understand the roles species play in their
communities.