Define population dynamics for multiple species from
a set of single-species dynamics objects and
defined pairwise interactions.
pairwise_interaction(target, source, masks, funs)population whose vital rates are affected by the pairwise interaction
population whose abundances affect the vital rates
of target
masks defining which vital rates are influenced by each function
functions that take vital rates and abundances of the
source population as inputs and return scaled vital rates
To be completed.