  We compare the bicategory of spans with that of bisets (a.k.a. bimodules,
distributors, profunctors) in the context of finite groupoids. We construct in
particular a well-behaved pseudo-functor from spans to bisets. This yields an
application to the axiomatic representation theory of finite groups, namely a
new proof and a strengthening of Ganter and Nakaoka's identification of Bouc's
category of biset functors as a reflective subcategory of global Mackey
functors. To this end, we also prove a tensor-monadicity result for linear
functor categories.
