This function allows you to plot a sample distributions with convex hull polygon (alpha shape).
The function is written to use distribution data obtained from (Neil Rosser): https://fusiontables.google.com/DataSource?docid=1tY_afZrv2-mmg0GwLjfVRZgePx_zh0r6S8AbE9s#map:id=3, but should work for any set of distribution tables that has column headers "lon_dec", "lat_dec" and "taxon_nombre".