Depending on the source 85% were murdered in the camp. Purportedly 960,000 Jews entered the camp and were immediately killed, gassed or otherwise. So no, starvation and disease were secondary.
When I was in school, I did a lot of research into this. Extermination (by all methods including shooting, hanging and gas) was the primary cause. If you died from disease/starvation it was because of the "backlog" in the process, or you were worked to death. Males (younger and healthier) survived longer because they were prime candidates for slave labor. Old people, women and children went right into the "disposal process."
