Browsing by Author "CONTRERAS, LC"

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    A LONG-TERM STUDY OF A SMALL-MAMMAL ASSEMBLAGE IN THE CENTRAL CHILEAN MATORRAL
    (1989) IRIARTE, JA; CONTRERAS, LC; JAKSIC, FM
    We livetrapped small mammals for 18 months with Sherman traps, and for 13 (simultaneous) months with Tomahawk traps, in a central Chilean matorral (chaparral-like shrubland) locality near Santiago. Eight species (the marsupial Marmosa elegans, the lagomorph Oryctolagus cuniculus, the cricetids Akodon longipilis, Akodon olivaceus, Oryzomys longicaudatus, and Phyllotis darwini, and the caviomorphs Octodon degus and Abrocoma bennetti) were captured, with total mean densities of 57.9 and 12.4 individuals per ha in the Sherman and Tomahawk grids, respectively. Tomahawk traps provided the same estimates of density for the two largest rodents, but did not capture small species or adult rabbits. Weights of adult individuals of four species were 20-30% smaller than those reported previously. Octodon and Oryctolagus used shrub cover as available; Abrocoma avoided dense patches, whereas the remaining five species avoided sparse patches. Six mammal species were associated with the six principal shrub species in proportion to their availability, but A. longipilis and Octodon both associated with Colliguaya odorifera more frequently than expected, while apparently avoiding two other shrubs. Stopwatch- timed captures allowed categorization of one small mammal as diurnal and diurnal-crepuscular, two as nocturnal, four as nocturnal and nocturnal-crepuscular; one species was active all day, except at dawn. Comparisons with similar assemblage studies conducted in neighboring matorral areas demonstrate marked differences in population densities of particular mammal species, apparently related to levels of habitat disturbance and associated reductions of shrub cover.
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    HETEROGENEOUS RESPONSES OF SMALL MAMMALS TO AN EL-NINO SOUTHERN-OSCILLATION EVENT IN NORTHCENTRAL SEMIARID CHILE AND THE IMPORTANCE OF ECOLOGICAL SCALE
    (1995) MESERVE, PL; YUNGER, JA; GUTIERREZ, JR; CONTRERAS, LC; MILSTEAD, WB; LANG, BK; CRAMER, KL; HERRERA, S; LAGOS, VO; SILVA, SL; TABILO, EL; TORREALBA, MA; JAKSIC, FM
    A prolonged El Nino Southern Oscillation (ENSO) event during 1991-1992 with three times the normal annual 85-mm rainfall was accompanied by major changes in numbers of small mammals at a semiarid Mediterranean site in northcentral Chile. Several demographic patterns were evident. Akodon olivacerrs, an omnivore, had a rapid increase in population size of more than an order of magnitude. Phyllotis darwini, a granivore-herbivore, showed somewhat delayed, smaller increases superimposed on annual oscillations. Octodon degus, an herbivore, showed a delayed response with larger increases and extended breeding in 1992-1993. Finally, Oligorzyzomys longicaudatus, a granivore, experienced increases during both a dry (1990, ppt = 32 mm) and a wet year (1992). Other species such as Aborthrix longipilis, Abrocoma bennetti, and Thylamys elegans had smaller, delayed demo,oraphic responses. Reproductive rates for the first three species were higher due to the ENSO event only in O. negus males and P. darwini as a quadratic function of time. Survival rates of all four principal species were significantly greater during the 1991-1992 ENSO. Finally, average movement between captures was lower during ENSO years, suggesting behavioral changes. Explanations for these patterns include rainfall-related increases in food-resource levels (A. olivaceus and P. darwini), the importance of source-sink processes in vagile species from more mesic, adjacent habitats (O. longicaudatus), and delayed responses to extrinsic events in species with long gestation (O. degus, A. bennetti). The heterogeneity of species responses suggests different capabilities for small mammals to respond to an extrinsic, large-scale event, and it emphasizes the importance of long-term studies in semiarid systems.
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    NATURAL-HISTORY OF MICROCAVIA-NIATA IN THE HIGH ANDEAN ZONE OF NORTHERN CHILE
    (1993) MARQUET, PA; CONTRERAS, LC; SILVA, S; TORRESMURA, JC; BOZINOVIC, F
    We document the first record of Microcavia niata in the high Andes of northern Chile near the border of Bolivia. This species is restricted to bog habitats where it principally feeds on grasses and aquatic plants. Its basal metabolic rate was 0.689 +/- 0.1 ml O2 g-1 h-1. Two colonies were studied, each possessing 15 and 17 individuals, and characterized by female-biased sex ratios. Individuals reacted aggressively against the intrusion of non-colony members and elicited alarm calls under risk of predation.
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    SPATIAL-DISTRIBUTION OF SOIL NUTRIENTS AND EPHEMERAL PLANTS UNDERNEATH AND OUTSIDE THE CANOPY OF PORLIERIA-CHILENSIS SHRUBS (ZYGOPHYLLACEAE) IN ARID COASTAL CHILE
    (1993) GUTIERREZ, JR; MESERVE, PL; CONTRERAS, LC; VASQUEZ, H; JAKSIC, FM
    Soil nutrients and density and biomass of annual plants underneath and outside the canopy of Porlieria chilensis shrubs were measured at the end of the growing season in a protected arid coastal site in Chile. Levels of soil nitrogen, phosphorus and organic matter were significantly higher underneath than outside the canopies of shrubs. Almost 4 times as many plants occurred outside than underneath shrubs, but no significant differences in total aboveground biomass were found. Several species had higher densities and/or biomass outside rather than underneath shrubs, whereas others showed the opposite trend. Species richness was lower underneath P. chilensis canopy. The spatial microdistribution of ephemeral species may be explained by differential water and nutrient requirements. Comparison of the patterns observed in our protected site versus surrounding unprotected areas supports the generalization that man, by removing shrubs and trees, has changed a previous heterogeneous spatial distribution of nutrients to a more homogenous one.