This book contains field and laboratory research that analyze how environmental and physiological factors influence agonistic interactions and the impact these interactions have on the development of dominance relationships and resource use. This book highlights the importance for understanding shelter availability, abundance, and quality in different natural systems to develop a clearer understanding that the impact of shelter use and preference, opponent size, and sex have on dominance relationships. Animals were also shown to exhibit different social behaviors during interactions. Male and female crayfish also engage one another in natural systems and make the choice to engage in agonistic bouts or mating behavior. Animals communicate during interactions and compete for both resources and mates that are essential for increasing an individual's fitness. Research on the underlying mechanisms that influence motivation can provide a clearer understanding of how to manipulate and alter aggression and the dominance relationships that are so prevalent in many animal systems.