Pro rata [1] is pretty standard [edit: at least in early stage startups], so investors typically have the option to maintain their level of ownership by putting money into the round. Everyone else gets diluted. I think in practice investors only get diluted if they actually want to. I'm not sure how often pro rata is extended to founders, but I would guess it's pretty common.
[1] https://techcrunch.com/2017/09/13/how-pro-rata-works-in-vent...