We have a five month old papillon puppy. We brought her home at 8 weeks old so I know she has never been deprived of anything and has always had plenty of food, toys, love and affection. Yet every time our cat (a 13 year old Manx) gets near anything of hers or even goes to "his" food bowl, she gets very aggressive and possessive. We've had a few run-ins with her growling at us over food but we put a stop to that quickly by putting her in a submissive position and then touching her bowl, her and her food over the next few days to make sure she knew we are the Alpha leader in this house.
She has a crate and a dog bed. We keep her in the crate at night but my husband is retired so she usually has the run of the house during the day. It seemed amusing when we noticed she was taking all her toys with her from place to place. We found her rope toy, squeaky lamb toy, ball and rawhide chew sticks all together where ever she decided to nest. She would make endless trips from crate in the bedroom to the bed in the living room carrying her toys from room to room. I'm thinking this was a sign that she is a bit more dominant than expected. We will continue to help her socialize and loose some of her possessiveness.
She weighs about five pounds. Our cat weighs 12 pounds and still has his claws. We were concerned at first, that he might really hurt her, but he shows amazing restraint when he's had enough and fights back. Only one time has he connected hard enough to cause her to yelp when he swatted her. (a miracle in itself)
I thought we'd had a breakthrough today. They were actually in the yard together without and barking or hissing. This lasted about 20 minutes, then they both seemed to have all the "truce" they could handle.
In the image above you can just see the cat's right paw just beginning to lift and his shoulders hunch for a strike. He swatted and hissed. She barked and chased. Truce over!
He ran behind a bush and she barked at him.
I'm beginning to think they both enjoy this stuff...