Degree distribution in plant-animal mutualistic networks: forbidden links or random interactions?

Abstract

Recent studies show that ecological interaction networks departfrom the ‘‘scale-free’’ topologies observed in many other realworld networks. Such a departure has been hypothesized to resultfrom non-matching biological attributes of species, such asphenology or morphology, that prevent the occurrence of certaininteractions (‘‘forbidden links’’). Here I compare the topology of17 plant/animal mutualistic networks with that predicted by asimple null model that assumes that a species’ degree (number ofinterspecific interactions) is a function of its frequency ofinteraction. The topology predicted by this null model isstrikingly close to that observed in the real networks. Thus, thisnull model provides a simple alternative interpretation of patternsobserved in ecological interaction networks that does not requirethe existence of non-matching species traits.