Function to compute trophic diversity indices # following Villeger et al. 2008 (Marine Ecology Progress Series, 364: 135-146)
Villeger, S., Miranda, J. R., Hernandez, D. F., Lopez, A. S., & Mouillot, D. (2008). Stable trophic structure across coastal nekton assemblages despite high species turnover. Marine Ecology-Progress Series, 364, 135–146