Erin Hunter, the pseudonymous author team whose credits include the Warriors and Seekers series from HarperCollins, has a new member. Scottish author Gillian Philip joins this creative stable as the author of the Survivors series, which recently launched with The Empty City. Featuring an apocalyptic setting, the fantasy centers on canines who have been abandoned by their humans. Survivors is a companion series to Warriors, starring felines who are similarly left on their own, which began in 2003 – and gave birth to Erin Hunter.

In less than a decade, the Warriors series has spawned a number of tangential story arcs, as well as special editions, field guides, and manga series; English-language editions have sold a total of 14 million copies worldwide.

The franchise was developed by HarperCollins and the London-based firm Working Partners, which creates original fiction series for publishers. That company’s Victoria Holmes developed the original storyline for Warriors, and was a founding member of the Erin Hunter author team, which also includes Kate Cary, Cherith Baldry, Tui Sutherland, and now Philip. Sutherland, who worked at HarperCollins when Warriors was conceived, was also the first in-house editor of the series.

Currently at the editorial helm of the Erin Hunter series – Warriors, Seekers (which debuted in 2008) and now Survivors – is Erica Sussman, executive editor of HarperCollins Children’s Books, who arrived at the house in 2004. All of the Erin Hunter series are created in close association with Working Partners, Sussman says. “Members of the Working Partners editorial team send me storylines and drafts of the manuscripts for every book, and we talk about them. It is very much a group discussion, and it’s great to have so many people to bounce ideas off.”

Philip, who has previously written stand-alone novels and series under her own name, and has been part of a different ghostwriting team, for Darke Academy (under the pseudonym Gabriella Poole), says she finds the team effort approach a very different experience from writing her own books, “because then I tend not to plot very much – it develops as it goes along. When the plot has been worked out as a team, you’re working with an outline. Changes are made, of course, as characters take on minds of their own and we all get to know them better. Sometimes I’ll e-mail the team editors and say that I don’t think a character would react that way. It’s a very interesting way to work.”

Last month, Philip visited the U.S. for the first time to embark on a five-city tour to promote The Empty City, and was thrilled by the enthusiasm of the young readers she encountered. “The reaction from everyone I met was fantastic,” she said. “Kids brought pictures of dogs to show me – it was absolutely lovely! I think a lot of readers are coming to Survivors through Warriors – children I met talked about both which cats they liked best from Warriors and which dogs they like best from Survivors – but it seemed that a lot of readers are discovering Survivors on its own.”

Philip has already finished the second Survivors novel, whose cover is revealed here. She says there are six installments planned, and then “we’ll see how it goes, though we hope to be able to do more series – as a team.” Writing under her own name and as Erin Hunter, does Philip ever grapple with her multiple author identities as she writes? “It’s never hard to keep them separate when I’m writing,” she says in response. “But sometimes, when I’m signing books, I have to stop and think. I try not to end up signing, ‘Gillian Hunter!’ ”

Survivors #1: The Empty City by Erin Hunter. HarperCollins, $16.99 Aug. ISBN 978-0-06-21056-0

Survivors #2: A Hidden Enemy by Erin Hunter. HarperCollins, $16.99 May 2013 ISBN 978-0-06-21026-7