Where does Ralph show a lack of cooperation in the beginning of the book that affects him later on?
The first quotation is a decision and the second one that proves it is the effect of the decision.
If I were to answer this question, I would look at Chapter 4, in which Ralph refuses to allow Jack a free pass on letting the fire go out when Jack and his group went hunting. Even though Jack kills his first pig, Ralph refuses to congratulate him, saying instead,
"There was a ship. Out there. You said you'd keep the fire going and you let it out!"
In the same scene, Ralph refuses to forgive Jack for breaking Piggy's glasses, repeating,
"That was a dirty trick."
Rlaph's decision to stand up to Jack, to call him out, so to speak, has enormous consequences in the novel. It is in this chapter that we see different priorities forming--Ralph wants rescue; Jack, fun. Ralph sides with Piggy, who also has rescue as a top priority. Ralph's refusal to cooperate with Jack in this scene, establishes a chasm between the two boys, who were initially friends. This animosity continues to grow until Jack eventually leaves the group (in Chapter 8) and starts a tribe of his own:
I'm not going to play any longer. Not with you!