Dear all, At CT2010 in Genova, I gave a talk on numerical invariants of enriched categories and their applications to measuring diversity. A paper giving some background is now available: Tom Leinster and Christina Cobbold, Measuring diversity: the importance of species similarity. _Ecology_, in press. http://www.maths.gla.ac.uk/~tl/mdiss.pdf As the name of the journal suggests, it was written for ecologists - but it should be accessible to mathematicians too. Best wishes, Tom [For admin and other information see: http://www.mta.ca/~cat-dist/ ]