Why do territory holders usually win. Convention as predicted by game theory.
Many studies demonstrate that body size in particular is related to success in holding a territory.
Beewolf wasp that sets up mating territories on harvester ant mounds. Size also important in the pseudoscorpion that I told you about that rides on the backs of beetles. Males set up territories on beetle back. However, part of the year, they live on trees and they are not territorial - being large is not an advantage. Therefore, residents are willing to invest more in keeping it.