In a not so different fantasy world, whose physics and thus are similar to our own how would including penguins affect the look and function of a typical arctic ecosystem.
For the purposes of this question, the Not-Arctic is functionally identical to our arctic, consisting of no major landmsses save a whole bunch of islands and some northern bits of larger continents below (think canada, scandinavia and/or siberia). As well its ecosystem is much the same, consisting primary of seals, polar bears, whales, krill, etc. . .
Could I add penguins to this ecosystem, without disrupting it too much. I would like them to act a bit like the penguins of south america with much lower populations mainly inhabiting some islands. But I also want to have plenty of seals and whales to hunt.
So how would penguins affect such an ecosystem and could they even evolve there in the first place.