A network-based measure of functional diversity in food webs.

Biodiversity is measured from various perspectives. One of them, functional diversity, quantifies the heterogeneity in species traits and roles in an ecosystem. One important aspect of species roles is their interactions with other species, i.e. their network role. We therefore investigate here functional diversity from the network perspective. Species differ in their network positions in a food web, having different interaction patterns. We developed a measure for quantifying the diversity in species interaction patterns in a food web. We examined the relationship between interaction diversity and several global network properties for 92 food webs. Our results showed that high interaction diversity occurs in sparsely connected and less cohesive food webs. High interaction diversity also occurred in food webs with more clusters and high network modularity. We also quantified several conventional functional diversity indices and demonstrate that they show little or no correlation with interaction diversity. Our proposed diversity index therefore provides a measure complementary to current concepts of functional diversity.