New dog & how they relate to original dog

[Pattie]

We recently aquired my dad's dog into our home & my (smaller ) male is now trying to show the (larger) female that she needs to know her place. Is this normal? He is usually pretty easy going with her (or other dogs) around. He is used to seeing her often both at our house & at my dad's house. She has been here for about 2 months & just in the past few days he has taken to rushing her & snapping at her when she tries to race in front of him when he hears some preceived danger. She looks dejected & looks like she has not a clue why he is coming after her. She is fine with this & with him most times. But she will go after him over food or today went after him when he was playing a game with me that did not involve her. She is much bigger than him. So I worry that she could hurt him. Should I just let them establish domain & ignore things as long as no one is getting hurt or should I maintain dominance for my litle guy since he is the one that is being displaced? He has been happy being an only dog & I know it is hard for him to not be our only focus, since he has always been in the past. I appreciate help from anyone who has been there, Thanks.

[Pattie]

Thanks Roosje: This helps. It is Madison who has domain here. I think this should be the case since it was always his house. Originally my dad's house was his domain before he needed more care than dad could give him. When Katie first came along she took over dad's house as her domain not realizing that it had already been Madion's space. I think that Madison never really relinquished his right to be the master of either home. He always took the best bed & always expected to be fed first & wants to be in the lead when he is walking, etc. But here more than at dad's house he knows that this is where he reigns & he does not want to give anything up even if Katie is almost twice his size.