Does the order of invasive species removal matter?

An island fox pup.

A case study from the Channel Islands off the coast of California provides resource managers with a good illustration of the importance of carefully considering the complex interactions between species before removing exotic plants and wildlife. Otherwise they could exacerbate the situation for species they are trying to conserve.

In the 1990's, three sub-species of the native island fox (Urocyon littoralis) were driven to near extinction on the Northern Channel Islands by predation from newly colonizing golden eagles (Aquila chrysaetos). An abundance of feral pigs (Sus scrofa) on the islands  lured the eagles and subsequently contributed to predation and decline of the foxes. Thankfully, the managers carefully considered which species to remove first. They theorized that removal of the pigs first would have intensified golden eagle predation on the foxes. So even though it was much more challenging, they removed the eagles first and subsequently removed the pigs (eagles are hard to capture and lethal removal was not politically feasible).

However, one pair of eagles evaded capture and nested on the island following pig removal. This gave the researchers the opportunity to see what would have happened had the managers not considered the order of removal and instead focused on pigs first. The researchers collected prey remains at golden eagle nests and found that the pair intensified their predation on foxes after the pigs were gone. This shows that had the managers removed pigs first, it likely would have hastened extinction of the island foxes.

--Reviewed by Rob Goldstein

Source:	PLoS ONE
Title:	Does the Order of Invasive Species Removal Matter? The Case of the Eagle and the Pig
Authors:	Paul Collins, Brian Latta, Gary Roemer
	a) Santa Barbara Museum of Natural History, Santa Barbara, California b) The Bird Group, Santa Cruz, California c) New Mexico State University, Las Cruces, New Mexico