The overpopulation of deer on the Gulf and San Juan Islands of BC and Washington State has been a concern of residents and biologists for years.
Researchers from the University of British Columbia’s Faculty of Forestry have now shown that seablush, a wildflower of endangered Garry Oak ecosystems throughout the Pacific Northwest, can adapt rapidly to become a large, showy plant over a metre tall where deer are absent, or a diminutive plant only centimeters tall where deer are present, but is nevertheless rapidly driven to extinction where deer are overabundant.
“We grew seablush from 12 island populations where they co-exist with or without deer in and outside of large ‘common gardens’ either exposed to or protected from deer,” says UBC Forestry PhD graduate Cora Skaien, co-author of the paper, Local adaptation in island populations of Plectritis congesta that differ in historic exposure to ungulate browsers. “Our results showed that seablush populations that have co-evolved with deer survive and reproduce much better than plants from islands without deer. However, even locally adapted populations are driven locally extinct where deer are overabundant and protection on cliffs or other areas inaccessible to deer are absent.”
Skaien noted that plants from Seablush populations which have co-evolved with deer survived better by staying shorter for longer into the growing season because they were detected and eaten by deer less often than taller, showier plants from islands without deer. Plants from islands without deer became tall early in the growing season, had large showy flowers, but experienced very high mortality with deer present.
Cora’s co-author, Dr Peter Arcese, UBC Forestry Faculty’s Forest Renewal Chair in Conservation Biology, explained that while many species in need of conservation in Canada appear to have some capacity to adapt to human-caused change in the environment, that capacity is likely to be constrained by the evolutionary history of the species in question. The current study indicates that deer densities typically encountered in the Gulf and San Juan Islands at present put Seablush and many other plant species at risk of extinction where deer remain overabundant.
By characterizing the adaptive potential of native plants and delineating limits on their ability to accommodate environmental change, Skaien and Arcese show how conservation biologists can anticipate and incorporate the evolutionary capacity of plants into area-based conservation plans for critically endangered Garry Oak ecosystems of the Pacific Northwest.