I am trying to trace an Elizabeth Forster who may have immigrated to the US between 1851 and 1861.

Marjorie Chamberlain's book: "Johannes Dyckman of Fort Orange and His Descendents" page 352 lists an
Elizabeth Forester/Foster married a David D. Dykeman on July 4, 1859 in Cannonvillle, Delaware County, NY.

Elizabeth was born August, 1839 in England and died January 4, 1918 in Wildmere, Alberta, Canada. They had 10 children, 6 of which died young. The 4 remaining children were James Frederick, Thomas G, Robert Wallace and Alice born 1867, 1869, 1876, and 1879 respectively.

I am wondering whether it was common to drop the 'r' in Forster or whether the Forster / Foster is really interchangeable.