There's a local amateur photographer/entomologist that takes the most amazing pictures of a particular family of insects, the Tiger Beetle family ( http://en.wikipedia.org/wiki/Tiger_beetle
). He knows their life cycle and habits, knows where to find them, and gets photos showing them in their native habitat doing what they normally do.
There's a better-known local-ish professional (Ph.D.) entomologist expert on army ants who has transitioned from being a very enthusiastic professor helping other entomologists gain the photographic skills to document field research, to being a part-time professor and most-of-the-time photographer giving insect photography and macro clinics to the public and leading insect photography tours. www.myrmecos.net
Passion about a topic, and some knowledge about the topic, can be part of the "soft skills" and can help one focus on a specialty, in the above cases, insect macrophotography.
The three or so Missouri Dept of Conservation professional photographer/media specialist/educator individuals have their own specialities. One is an amateur astronomer (lucky for him he lives in a dark-ish sky area) and has for years taken "astro-landscape" photos, well before those photos became popular. Another is a bird and mammal specialist. One Conservation Dept photographer self-published a very detailed and very well photographed book on the prairie grouse family ( http://www.savethelastdancebook.com/
Some of the less-covered specialties are taken care of by amateurs or professors: herpetology, insects and spiders, etc.
When you learn to see something, you want to learn more about it, and the more you learn about it, the more you see the next time you go to photograph the subject.