title: Numerical and functional response of predators to a long-term decline in mammalian prey at a semi-arid Neotropical site.
abstract: Occurrence and diet of ten carnivorous predators (four falconiforms, four owls, and two foxes), and population levels of their mammalian prey, were monitored over 45 months at a semi-arid site in north-central Chile. Early in this period, small mammals irrupted and then declined markedly to a density 7% of that at peak. All four falconiforms (Buteo polyosoma, Falco sparverius, Geranoaetus melanoleucus, Parabuteo unicinctus) and one owl (Tyto alba) responded numerically to the decline in mammalian prey by virtually abandoning the study site. The three other owls (Athene cunicularia, Bubo virginianus, Glaucidium nanum) and the two foxes (Pseudalopex culpaeus and P. griseus) remained. With few exceptions, throughout the study predators maintained species-specific preferences among small mammal species regardless of the absolute and proportional abundance of these prev. At no time did the two prey species most responsible for the irruption (the rodents Phyllotis darwini and Akodon olivaceus) occur in predators' diets out of proportion to their estimated relative abundance in the field. Predators were clearly unable to prevent the irruption from occurring. Given the absence of a clear functional response to the most irruptive species, predators seemed unlikely to have been responsible for the observed crash. At present, however, predators may be prolonging the crash and delaying the return of small-mammal populations to typical densities.
authors.affiliation: Departamento de Ecología, Universidad Católica de Chile, Casilla 114-D, Santiago, Chile.
authors.forename: F M
authors.initials: FM
authors.lastname: Jaksié
authors.affiliation: Departamento de Ecología, Universidad Católica de Chile, Casilla 114-D, Santiago, Chile.|Department of Wildlife and Range Sciences, University of Florida, 32611, Gainesville, FL, USA.
authors.forename: J E
authors.initials: JE
authors.lastname: Jiménez
authors.affiliation: Departamento de Ecología, Universidad Católica de Chile, Casilla 114-D, Santiago, Chile.
authors.forename: S A
authors.initials: SA
authors.lastname: Castro
authors.affiliation: Department of Zoology, University of Florida, 32611, Gainesville, FL, USA.
authors.forename: P
authors.initials: P
authors.lastname: Feinsinger
keywords: Chile; Functional response; Mammalian decline; Numerical response; Vertebrate predators