The Channel Islands off of Southern California, often referred to as "the North American Galapagos" constitute a series of eight islands. Scoured by winds, surrounded by giant kelp forests the eight islands contain a number of rare and/or endemic flora and fauna. Although within a hundred miles of the tens of millions of people of southern California the islands constitute what many consider the most pristine view of southern California prior to freeways, Disneyland, and In N' Out burgers.
However this is not to say that our stewardship of these islands has not been without pitfalls...
Piglets, Fennel, Eagles and Foxes: An Ecological Cascade
Prior to the establishment of the Channel Islands as a national park in the 1980's decades of ranching had established feral populations of several hoofed mammals on many of the islands. The largest and most ecologically diverse of the islands, Santa Cruz- the island we will be concentrating on-, supported several thousand feral pigs. Heavy grazing, trampling of vegetation and especially rooting by the pigs disrupted native vegetation patterns which had evolved without native hoofed mammals. Invasive non-native grasses and herbs such as fennel were able to out compete the natives in these disturbed habitats.
|Santa Cruz Island Bird's- Foot Trefoil. Lotus argophilus var, niveus. Endangered.|
However the big victim in this ecological unfolding act was the endemic island fox. In an interesting and very illuminating series of calamities feral pigs, golden eagles, and bald eagles shaped the fate of these smallest of North American canids.
|Urocyon littoralis- the Island Fox|
Feral pigs are prolific breeders and they eventually outgrow the size where they are potential prey to the eagle so they can absorb the predation from the bird. Island foxes however have at most one litter every year, are prey size their whole life, and also diurnal like the eagle. And due to the relentless scouring of the earth by the pigs the vegetation cover is diminished leaving foxes more exposed to the eagles. So what we have here is golden eagles eating both piglets and foxes, but with foxes taking it on the chin from the aerial predator with a much more disproportionate hit. And stemming from this predation pressure a precipitous decline of the fox started in the 1990's.
|Golden Eagle predation of Island Fox|
|Sus scrofa- feral pigs|
There is literally SOOOO MUCH that can be taken from my all too brief synopsis of the events that transpired on Santa Cruz Island that one can literally come up with a whole semester ecology/environmental policy upper division college class on it. But my reasons for writing this post have nothing to do with any of these reasons you might be thinking of. You see competitive exclusion, invasive species and trophic cascades are all fine and dandy but what I am really aiming at here is the connection of the events that occurred on Santa Cruz Island to the islands' prehistoric ecology....
You see feral pigs were not the first large mammalian herbivore to inhabit the islands...
More to come- tune in later for This Island Earth Part II- Don't Tread on Me!!!
Restoring Santa Cruz Island
Island Pig Eradication Completed. LA Times
USC Dornsife Saving the Santa Cruz Island Fox