In the animal kingdom, there are many things that can influence behavior but generally we look at emotions as being the primary driver (stimulus) for behavior while reinforcement or punishment determines whether that behavior will be repeated in the future.
Stimulus - Emotions: Jaak Panksepp’s book Affective Neuroscience has one of the most widely known categorizations of human and animal primal emotions. As an expert in neuroscience, Jaak studied the brain, performed laboratory experiments and categorized basic emotions (brain systems) as follows: RAGE, FEAR, LUST, CARE, PANIC (Grief), SEEKING and PLAY.
The names were capitalized by Dr. Panksepp to highlight them as identified brain systems, as opposed to their use in the vernacular.
This system of emotions, how the individual reacts to them, and whether their reaction is rewarding or punishing, results in the creation of a resource access hierarchy between individuals. So, what we call dominance, is just a connection between emotions driving behaviors and behaviors being rewarded (success) or punished (unsuccessful).
Furthermore, researchers have also noted that just because an individual gains access to a resource first, does not mean they won’t follow another horse’s lead or choices in other situations. Nor does it mean that an individual with first access is the “alpha” of the entire group, in every situation.   Resource access and leadership can vary between individuals, group