Browsing by Author "CASTRO, SA"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    GERMINATION RESPONSES AND RESIN PRODUCTION OF GRINDELIA-GLUTINOSA AND G-TARAPACANA FROM THE ATACAMA DESERT
    (1995) CASTRO, SA; FUENTES, ER; TIMMERMANN, BN
    Germination responses and early seedling growth were examined for Grindelia glutinosa and G. tarapacana, two species that preliminary held and laboratory results had suggested could become a new resin crop for the hyper-arid Atacama desert in northern Chile. Initially we examined the germination responses to cold stratification and soil moisture. Stratification inhibited the germination of both species, but mostly of G. tarapacana. Best germination was obtained with about 50% soil moisture levels. Based on these results, we carried out factorial experiments with both species, two levels of nutrients and two levels of soil moisture. Although significant differences were not detected for the growth rate of the species, both benefited from nutrient and humidity additions. Germination rate of G. glutinosa was, in all cases, significantly higher than that observed for G. tarapacana. Resin yields were 17% for G. glutinosa and 26% for G. tarapacana, very high compared with the yields of other species in the genus.
  • No Thumbnail Available
    Item
    NUMERICAL AND FUNCTIONAL-RESPONSE OF PREDATORS TO A LONG-TERM DECLINE IN MAMMALIAN PREY AT A SEMIARID NEOTROPICAL SITE
    (1992) JAKSIC, FM; JIMENEZ, JE; CASTRO, SA; FEINSINGER, P
    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 small-mammal populations to typical densities.