It's neither expected nor customary to tip servers at breakfast and lunch -- or even at dinner, for that matter, except at the final dinner.
At the final dinner, you present tip envelopes (supplied) to your server, assistant server, and head server. Those tips are for all the service you've recieved at all meals over the entire course of your cruise. Many of us tip way more than the suggested amounts, because we understand that we're not just tipping for dinner and that the service tends to be excellent.
Although your breakfast and lunch servers will usually not be the same servers who serve you dinner, they'll be other guests' dinner servers -- so it all works out if everyone tips their dinner servers.
The only exceptions are:
-- Automatic 15% gratuities, which you can increase, are added to paid beverages at the time that you buy them.
-- At Palo, there is a service charge, which you can (and really should) increase.
-- Room service is tipped in cash at the time that service is rendered.