Which neurotransmitter affects neurons involved in voluntary movement, learning, memory, emotion, and possibly, response to novelty?

Dopamine

Explanation: Dopamine are chemicals produced by the nerve cells called neurotransmitters, The are used as a communication pathway to different parts of the brain and other body parts. They are mainly involved in voluntary movement, emotion and cognition.

Significant medical disorder such as tourette syndrome, Parkinson's disease, bipolar disorder and schizophrenia could result due to malfunction or insufficient production of Dopamine.

on island x the species needed to adapt because they were being subject to predators which didn't inhabit island y.  

density and pressure