Browsing by Author "Gutiérrez, JR"

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    The interplay of biotic and abiotic factors in a semiarid Chilean mammal assemblage
    (1999) Meserve, PL; Milstead, WB; Gutiérrez, JR; Jaksic, FM
    Since early 1989, we have conducted a large-scale ecological manipulation in a semiarid thorn scrub community in north-central Chile. We have excluded vertebrate predators (raptors and mammalian carnivores), and larger small mammal herbivore/competitors (i.e., degus, Octodon degus) from replicated 0.56-ha plots, and monitored small mammal population and plant responses over more than ten years. Repeated measures ANOVAs on minimum number known alive (MNKA) estimates of small mammals for a six-year period (1990-1996) spanning an El Nino event in 1991-1992 showed strong responses of some species to predator exclusions (e.g., O. degus; Darwin's leaf-eared mouse, Phyllotis darwini; the chinchilla-rat, Abrocoma bennetti). However, responses varied in time with significant effects during pre-El Nino (1990-1992) and El Nino (1992-1994) periods (i.e., 0. degus), or pre-El Nino and post-El Nino (1994-1996) periods (P. darwini. A. bennetti). Other species showed no responses to predator exclusions (e.g., olivaceous field mouse, Akodon olivaceus; long-haired field mouse, Abrothrix longipilis; long-tailed rice rat, Oligoryzomys longi caudatus). Some effects of competitor (degu) exclusions were detected (e.g., A. bennetti during the El Nino and post-El Nino periods; O. longicatrrlntus during the El Nino). "Top-down," factors (i.e., biotic interactions) appear to have greater effects on "core species" (i.e., P. darwini, O. degus) which persist in the thorn scrub. Other species (e.g., A. longipilis, O. longicaudatus) are transitory residents or "opportunistic" with lesser effects of biotic interactions, and their populations may be controlled by source-sink dynamics. All species had strong, responses to the 1991-1992 El Nino indicating primary control by "bottom-up" factors.
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    Vegetation in an altitudinal gradient along the Rio Loa in the Atacama Desert of northern Chile
    (1998) Gutiérrez, JR; López-Cortes, F; Marquet, PA
    Six sites between 0 m and 4000 m were sampled for plant and soil chemical characteristics along the Rio Loa, Atacama Desert, Chile. Sites located between 0 m and 1500 m showed lower species richness, higher plant cover and higher herbaceous productivity than the upper part of the altitudinal gradient. The number of species varied non-linerly with precipitation along the altitudinal gradient. Plant cover and herbaceous productivity in the lowlands is characterized by the Pluchea absinthioides-Distichlis spicata association of anthropic origin. We propose that vegetation structure along the altitudinal gradient has been affected by past and present human activities, and climatic and edaphic factors. (C) 1998 Academic Press.