Browsing by Author "Silva, SI"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    A long-term study of vertebrate predator responses to an El Nino (ENSO) disturbance in western South America
    (1997) Jaksic, FM; Silva, SI; Meserve, PL; Gutierrez, JR
    We analyzed the putative effects of the El Nino Southern Oscillation (ENSO) of 1991-92 in a semi-arid locality of northern Chile. We obtained 30 months of pre ENSO data, followed by 36 months of peak and post ENSO data (total = 5.5 yr). The rainy winter of 1991 resulted in a three-fold increase in total seed bank (perennial and ephemerals pooled) and in ephemeral (but not perennial) herb cover. Seed and herbage eaters (rodents) irrupted to population levels ca 20 times higher during the breeding season of 1991 than the preceding wintering season. Diurnal carnivorous predators (hawks, owls, and foxes) showed a delayed response to the irruption, increasing from seven individuals sighted during the wintering season of 1991 to 13 during the wintering season of 1992. A seemingly counterclockwise trajectory of predator abundance versus prey levels suggested a pattern of prey-driven dynamics, but confidence intervals were likely broad. In this semiarid locality, it appears that ENSO effects did not cascade down from higher to lower trophic levels, but rather the opposite. In this bottom-up scenario, we predict that as primary productivity varies with rainfall, so should secondary (mammal prey densities), and tertiary productivity (vertebrate predators). Long-term monitoring of this terrestrial ecosystem is needed to test this prediction.
  • No Thumbnail Available
    Item
    Interplay between metabolic rate and diet quality in the South American fox, Pseudalopex culpaeus
    (2004) Silva, SI; Jaksic, FA; Bozinovic, F
    We studied the metabolic costs associated with the ingestion of peppertree fruits (Schinus molle) in the culpeo fox, Pseudalopex culpaeus, the second largest canid in South America. Throughout its range of distribution, this fox feeds on rodents and other small vertebrates, and also on peppertree fruits, which represent 98% of total fruits consumed in semiarid Chile. Peppertree contains a high diversity of phytochemicals. Foxes feeding on diets containing rats and peppertree fruits (mixed diets) exhibited a 98.9% increase in basal rate of metabolism when compared to rat-acclimated foxes. Thus, acute ingestion of chemically defended fruits has an energetic cost for the fox, reflected in higher values of basal metabolism. Increased metabolic rates may be associated with increased protein synthesis for detoxification and for tissue repair, including the production of biotransformation enzymes. (C) 2003 Elsevier Science Inc. All rights reserved.
  • No Thumbnail Available
    Item
    Nutritional ecology and digestive response to dietary shift in the large South American fox, Pseudalopex culpaeus
    (2005) Silva, SI; Jaksic, FM; Bozinovic, F
    We tested the role of dietary shifts (from rodents to fruits and to mixed diets) oil the nutritional ecology of the culpeo fox Psendalopex culpaeus, a native canid of South America. We studied the effects of food quality oil digestive processes. nutrition, and mass balance, and the implications of diet quality for fox Survival. We observed at the end of the nutritional trials that body mass differed significantly between the three diet groups (fruits, rats and mixed diets), while percentage of body mass change differed significantly only ill the fruit diet treatment. Foxes fed with fruits consumed more food to meet their dietary and metabolic needs. Across diets, dry-matter as well as energy digestibility increased significantly with diet quality. Also, mean retention time was negatively and significantly correlated with dry-matter intake. We put forth that mixed diet may yield higher assimilation efficiencies and hence higher nutrient intakes than those predicted from the ingestion and assimilation of pure diets (i.e,. only rats, only fruits). We hypothesize that during periods of low availability of mammalian prey, a mixed diet should yield a positive energy/mass balance for the fox. We Conclude that temporal and spatial variation in nutrient, energy, and water contents of prey available in a given habitat could have all important effect on fox nutrition, energy use, and mass balance. Finally, we postulate that P.culpaeus Could not survive on fruits only past seven days.