I was taught that it varies for every dog, not by breed. In Giorgio, his normal temp is 101.5, as is Cybill's (Toy Poodle). I don't know what his low is, but, surely any drop by 2 degrees would be significant in an animal with a normally high body temperature.
Shame on me, I haven't measured Cherrish's normal resting temperature yet, and, I should.
I was also taught to take their temp. when they are normal, record it somewhere you can find it, so that we can know when they are in fact running a fever or have a sub-normal temperature.