Numerical and Functional Response of Predators to a Long-Term Decline in Mammalian Prey at a Semi-Arid Neotropical Site

• Published in: Oecologia Vol. 89; no. 1; pp. 90 - 101
• Main Authors: Jaksić, F. M., J. E. Jiménez, S. A. Castro, Feinsinger, P.
• Format: Journal Article
• Language: English
• Published: Berlin Springer-Verlag 01-01-1992; Springer
• Subjects: Animal and plant ecology; Animal traps; Animal, plant and microbial ecology; Aves; Biological and medical sciences; Diet; Feces; Foxes; Functional responses; Fundamental and applied biological sciences. Psychology; Mammalia; Mammals; Owls; Predators; Synecology; Terrestrial ecosystems; Vertebrates; Winter; South America; Chile; America; Predator prey relation; Fissipedia; Population regulation; Carnivora; Bubo virginianus; Population decline; Raptor; Feeding; Prey; Vertebrata; Mammalia; Falco sparverius; Diet; Semi arid zone; Tyto alba; Aves; Mammalian decline; Functional response; Chile; Vertebrate predators; Numerical response
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/BF00319020

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 prey. 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 smallmammal populations to typical densities.