"Resource guarder" is referred to as a temperament trait since puppies are born with varying degrees of this instinct to guard limited resources. It is derived from a primitive survival instinct inherent of all wild canines regardless of dominant or submissive position.
Some puppies are born with a very low instinct to resource guard and it is very easy for a person or dog to pull even a steak away from the dog. Other puppies seemingly guard anything that they find remotely interesting, such as feathers and pen caps.
As with all temperament traits, behavior modification and training can do much to mold and control the behaviors. But, when it comes to extremes a person can do just about everything wrong with some dogs and the behavior of resource guarding may not emerge and another dog will always show resource guarding to some degree even if everything is done to prevent the behavior.
Historically many breeds were selectively bred for low levels of resource guarding, especially if the dogs were expected to retrieve dead game to a handler. With other breeds it was not a high priority unless the instinct was causing problems with the human interaction.
Since pronounced resource guarding is a normal and natural behavior it must be noted that without careful selective breeding to maintain low levels of resource guarding this trait can easily revert back to more pronounced levels within a few generations.