Comment:

To determine how network architecture affects network stability, we calculated the robustness of each network. Rather than describing network architecture itself, robustness quantifies a network’s ability to retain its structure following the removal, or extinction, of species (Dunne et al. 2002). We simulated extinction by removing plant species and observing which pollinators were left without forage resources. Pollinator species were considered to go “extinct” when all of their plant hosts had been removed from the network. We used the bipartite package in R to execute a removal algorithm in which plant species were removed at random without replacement. Although either plants or pollinators could have been removed in the simulation, we chose to remove plant species because in a restoration context, the presence and absence of plants is usually manipulated rather than the pollinators. Simulations were repeated 999 times for each network. We used the technique developed by Borgo et al. (2007) to quantify the robustness with a single parameter r, which ranges from 0 to 1. A network in which r approaches 0 is considered fragile, such that even if a very few plants are eliminated, most pollinators would go extinct. Likewise networks with r approaching 1 are considered robust.