A field of spring wildflowers, abuzz with busy insects seeking nectar and spreading pollen, may look like a perfect model of random interaction. But ecologists have discovered order within this anarchy. For instance, as the number of species grows, the number of interactions does too, while the connectivity (the fraction of possible interactions that actually occur) and the nestedness (the relative importance of generalist species as mutualistic partners of specialist species) shrinks. Study of such networks of species is still in its youth, and the rules that generate these patterns of interaction are still being worked out. In a new study, Luis Santamara and Miguel Rodrguez-Girons propose that two key mechanisms, trait complementarity and barriers to exploitation, go a long way in explaining the structure of actual networks of plants and their many pollinators.
The two mechanisms each arise from fundamental aspects of the interaction between species. An insect will be unable to reach nectar in floral tubes longer than its proboscis; the tube length sets up a barrier to some species, but not to others. Each plant species also has a given flowering period. The specific activity period of each insect species will complement the flowering of some plant species more than others. Other barriers and other complementary traits have been described for a variety of plantpollinator pairs. To explore the significance of these mechanisms, the authors modeled plantpollinator interaction networks using a few simple rules, and compared their results to data from real networks in real plant communities. The models incorporated from one to four barrier or complementary traits, or a combination of two of each. They also tested two variations of a "neutral" interaction model, in which species interact randomly, based simply on their relative abundance.
Different models did better at mimicking different aspects of real networks, but the two that performed best
Contact: Natalie Bouaravong
Public Library of Science