Browsing by Author "MESERVE, PL"

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    EFFECTS OF VERTEBRATE PREDATION ON A CAVIOMORPH RODENT, THE DEGU (OCTODON-DEGUS), IN A SEMIARID THORN SCRUB COMMUNITY IN CHILE
    (1993) MESERVE, PL; GUTIERREZ, JR; JAKSIC, FM
    The effects of vertebrate predation have been monitored since 1989 on 16 replicated 0.56 ha study plots in a semiarid thorn scrub community in north-central Chile. Using fences of different heights with and without holes and suspended game netting to alter principal predator (foxes and raptors) and large rodent herbivore (Octodon degus) access, four grids each have been assigned to the following treatments: 1) low fencing and holes allowing free access of predators and small mammals; 2) low fencing without holes to exclude degus only, 3) high fencing and netting with holes to exclude predators only; and 4) high fencing and netting without holes to exclude predators and degus. Small mammal population censuses are conducted monthly using mark-recapture techniques. Degu population trends during 1989 and 1990 showed strongly but nonsignificantly lower numbers in control plots during months when densities were characteristically low (September November) for this seasonally reproductive species; since March 1991, differences have become persistent and increasingly significant. Predators appear to have greater numerical effects when their prey populations are low. Survival times of degus, particularly established adults, were significantly longer in predator exclusion grids during the 2 1/2 years of observation; thus, predation also affects prey population structure.
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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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    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.