Sunday, August 14, 2016

Island Fox Rebounds Like a Superball

The tiny Chanel Island Fox (Urocyon littoralis) of Santa Cruz and surrounding islands has had the fastest successful recovery of any Endangered Species Act (ESA)-listed mammal ever.

At their lowest point, the fox numbers had dwindled from 1,780 to only 15 on Santa Rosa Island, from 450 to 15 on San Miguel Island, and from more than 1,400 to 55 on Santa Cruz Island.

Ironically, the fox decline was primarily due to fox predation by golden eagles which had replaced Bald Eagles lost to pesticide abuse some 50 years earlier.

The Island Fox rebound was accomplished relatively quickly by trapping and relocating the Golden Eagles, reestablishing bald eagles to their historic territories, and vaccinating fox for canine distemper. The fecundity of Mother Nature did the rest.

As of 2015, there were approximately 700 foxes on San Miguel Island, 1,200 on Santa Rosa Island, and 2,100 on Santa Cruz Island. The Santa Catalina Island population is estimated at around 1,800 foxes; however disease remains an ongoing threat to this subspecies.


Peter Apps said...

By happy coincidence you run two stories back to back with something important in common - small founder populations and closed gene pools - the foxes because they are on an island and the flat-coated retrievers because they are a kennel club breed with a closed registry.

The difference is that the island foxes will still be subject to natural selection, which will weed out animals that are homozygous for deleterious genes, leading to a population of reasonably healthy animals with normal lifespans.

PBurns said...

The Island Fox have been pretty well studied. They are a type of Gray Fox that has shrunk in size. Probably introduced by man as a pet some 10,000 year ago, with each island having some genetic variation due to drift. Genetic bottle neck is an issue, but it's not as serious as all that -- fox appear to have been introduced to various islands at various times, and so a little "genetic seeding" would be par for the course and fit history well enough.

Peter Apps said...

I'm sure the foxes will do just fine. In general wild populations can tolerate quite high levels of inbreeding after population bottlenecks simply because defective individuals die young - you don't make it to breeder status if your muzzle is too short or your hips are crippled. Cheetahs were found to have very low levels of genetic diversity following two bottlenecks, but nobody has been able to show any effect of this on the survival of wild cheetahs. On the other hand the Isle Royale wolves died out after multiple generations of line breeding, and lions in Hluhluwe-Umfolozi had genetic abnormalities from inbreeding, but these were both persistently small populations sealed off from immigrants.