"Year Firsts Count" graph
Add a new "Year Firsts Count" graph. It would look much like the current Year Species Count graph, but instead of showing the species count for each year it would show the number of lifers/firsts (filterable) for each year.
After discussion via Facebook & Twitter this was considered a "nice to have" rather than "must have", etc. Feel free to vote for it if you would like to see it added!
(It's pretty easy to do.)
Edward King commented
Yes, definitely. Does it have to be locked to filtering by Year as opposed to an open date range? That would surely provide more flexibility to users.