Taylor, 25, has signed an 18-month deal with Pompey after he was released by Bristol City.
He told the club website: "I'm very happy to be here and I just want to start playing some games now.
"I've been sat on the bench at Bristol City and asked the manager if I could leave. He said yes and when I heard that Pompey were interested it was an easy decision.
"It's a club with a massive fanbase and I can't wait to show the supporters just what I can do."
Jervis is back at Fratton Park, subject to international clearance, having had a brief spell on loan with Pompey last term.
The 22-year-old striker was a free agent after leaving Turkish side Elazigspor and has signed a contract until the end of the season.
He said: "I'm delighted to sign at last. I can't wait to get out onto the pitch and start playing for Pompey again."
Former Reading full-back Shorey, 32, has also signed a deal until the end of the current campaign.