Environmental Engineering Reference
In-Depth Information
Fig. 15.2
Hyperpredation relationships on Santa Cruz Island, involving a
colonizing predator (bald eagle), an introduced prey (pig), and two native prey
(insular fox and striped skunk). Photo: Gary Roemer.
controlling only the introduced prey is unsatisfactory in the long term because
predators could place high predation pressure on the indigenous prey. h roughthe
use of models, Courchamp
et al
. (2003b) determined that a regime of combined
control of both introduced species (predator and prey) is the best restoration strat-
egy in such cases. h ey noted that if the control of introduced prey is not su cient,
the indigenous prey will be destroyed, even if the predator population is being
controlled, while too high a prey control would cause the predator to shift to local
prey. Courchamp and Caut (2005) advocated the simultaneous commencement
of both control programmes; beside being the most ecologically viable option,
costs may be reduced (if transportation, or hunting and trapping can be shared)
and e ciency increased (e.g. through the additive eff ects of primary and secondary
poisoning of predators (Robertson
et al
. 1994; Torr 2002).
h e interaction between introduced pigs (
Sus scrofa
) and native golden eagle
(
Aquila chyrsaetos
) populations on Santa Cruz Island, California, provides
an example of bottom-up regulation as well as the presence of hyperpredation
(Fig. 15.2) (Roemer
et al
. 2002; Courchamp and Caut 2005). h e consequences
of these processes on endangered island grey fox (
Urocyon littoralis
), as well as the
management implications for native predators, are discussed next.
h e endemic island grey fox occurs only on the Channel Islands, and has evolved
over the past 20,000 years to such an extent that the largest six islands have their
own endemic subspecies (Roemer
et al
. 2001). Severe declines had been noted in
the fox populations, and were initially attributed to predation by golden eagles
