Browsing by Author "FEINSINGER, P"

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    BIRD ASSEMBLAGES IN TEMPERATE FORESTS OF NORTH-AMERICA AND SOUTH-AMERICA - A COMPARISON OF DIVERSITY, DYNAMICS, GUILD STRUCTURE, AND RESOURCE USE
    (1991) JAKSIC, FM; FEINSINGER, P
    Using available data on entire bird assemblages of temperate forests in North and South America, we compare ecological patterns and dynamics between continents and suggest a comprehensive but low-cost research program to fill some of the many conspicuous gaps in the present state of knowledge. The scanty data available for comparison suggest that ecological trends of avifaunas are reasonably similar between grossly similar forest types on the two continents, but that important dissimilarities also occur due to different phylogenies, geologic histories, compositions of vegetation, and climate. For example, fruits apparently provide a steadier resource base in South America than in North America, whereas masting seed-, nut-, and cone-bearing trees, and "masting" insect larvae seem more prevalent in North than in South America. Accordingly, the South American avifaunas studied to date contain substantial proportions of frugivores or frugivore-insectivores, whereas North American avifaunas appear to contain larger numbers of opportunistic species and/or seed-, nut-, and cone-feeding species. We propose that North American temperate forests are more heterogeneous, seasonal, dynamic, and irruptive than their South American counterparts, from a bird's eye view. The consequence could be that South American avifaunas are less opportunistic than their North American counterparts in response to spatiotemporal heterogeneity in resources or community structure; that is, they migrate less over short and long distances. Nevertheless, data are not available to test this assertion. We propose a careful comparative study of avifaunas in evergreen and nearby deciduous forests on both continents.
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    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.
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    SPATIOTEMPORAL PATTERNS OF AN IRRUPTION AND DECLINE OF SMALL MAMMALS IN NORTHCENTRAL CHILE
    (1992) JIMENEZ, JE; FEINSINGER, P; JAKSIC, FM
    During the austral winter of 1987 (June-August) at a semi-arid site in northcentral Chile, an outbreak of small mammals apparently was triggered by one episode of unusually high rainfall. From October 1987 to November 1990, we monitored the outbreak on a monthly basis on two equatorial- and two polar-facing slopes. Overall density on equatorial-facing slopes was 239 individuals/ha in spring 1987, increasing to a peak of 404/ha by summer 1988, and then steadily declining to a crash of 20/ha (5% of peak density) by spring 1990, with no signs of recovery. On polar-facing slopes, mammalian abundances were about one-half those of equatorial-facing slopes. There were 112 individuals/ha in spring 1987, increasing to a peak of 199/ha by summer 1988, and then steadily declining to a crash of 8/ha (4% of peak density) by spring 1989. Since then, mammal populations on polar-facing slopes have been slowly recovering, reaching 11% of their peak density by November 1990. Of the eight species monitored, only three irrupted: the granivorous cricetid Phyllotis darwini, the omnivorous cricetid Akodon olivaceus, and the insectivorous didelphid Marmosa elegans. These three irrupted and declined in phase, simultaneously on the two opposite-facing slopes, such that their relative frequencies did not shift markedly. Two of the three folivores (Abrocoma bennettii, Octodon degus, but not Chinchilla lanigera), one granivore (Oryzomys longicaudatus), and one insectivore (Akodon longipilis) disappeared from the site, persisting longer on equatorial-facing slopes.