That is the Amazon Long Term Bonus1. I'm playing as Amazon and after defeating animals I get food as a bonus resource. What causes this to happen? I can't find a reason for this to happen in the Hero abilities section.

No Max, you can just scroll the abilities bar or select them from the Unit/Hero Panel.2. What's the limit on the number of abilities you can have? If there is a max, how do I choose which abilities I have?