What is the correlation between Bitcoin and ether?

In the dynamic world of cryptocurrency, understanding the intricate relationship between the leading digital currencies is paramount. Could you elaborate on the correlation between Bitcoin, the original and most well-known cryptocurrency, and ether, the native currency of the Ethereum blockchain? Do they tend to move in tandem, with price fluctuations mirroring each other? Or is there a more nuanced relationship, where external factors or the unique features of each currency drive their respective movements? Understanding this correlation could provide valuable insights for investors and enthusiasts alike.