LOS ANGELES (AP) — PBS’ “Masterpiece” marks its 50th anniversary Sunday. The drama and mystery showcase could rest on its reputation built with acclaimed programs including “I, Claudius” and “Elizabeth R” and polished anew by surprising pop-culture hits “Sherlock” and “Downton Abbey.” But “Masterpiece” executive producer Susanne Simpson says it’s positioned to thrive as it addresses the challenges posed by a changing media industry and increased calls for diversity. Streaming services and other outlets are gobbling up the British-made dramas that are a “Masterpiece” staple, forcing the showcase to become more aggressive in the marketplace. The new season of “Masterpiece” begins Sunday with a reboot of “All Creatures Great and Small.”