Browsing by Author "Fuentes, Eduardo"

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    Diterpenoids from Grindelia tarapacana
    (1995) Zhou, Lin.; Fuentes, Eduardo
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    European rabbits versus native rodents in Central Chile: effects on shrub seedlings
    (1983) Fuentes, Eduardo; Jaksic Andrade, Fabián; Simonetti, Javier A.
    The importance of the introduced rabbit Oryctolagus cuniculus and of the native rodent Octodon degus (=degu) as browsers of shrub seedlings in the Central Chilean evergreen shrublands (=matorral) was experimentally assessed. Seedlings were planted in several spatial arrangements in two open successional stands and in two mature stands of different cover and exposure. The browsing impact of rabbits and degus was evaluated separately after about one year since the start of the experiments. It was found that degus cause important seedling mortality only within a 5 m-radius centered at the border of their retreats. Rabbits, on the other hand, cause heavier seedling mortality, forage more widely, and consequently have a greater impact than do degus. It is speculated that rabbits may be halting the secondary succession process, shifting the matorral composition toward less palatable shrub species, and/or broadening the spacing between shrub clumps.
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    Landscape change under indirect effects of human use: the Savanna of Central Chile
    (1989) Fuentes, Eduardo; Avilés, Reinaldo; Segura, Alejandro
    The Chilean Intermediate Depression to the north of Santiago has experienced a physiognomical transformation from a Prosopis chilensis woodland to an Acacia caven savanna. Today P. chilensis trees are scarce and belong mostly to the larger size classes. By contrast A. caven seems to reproduce frequently and its populations consist of individuals of all size classes. In this paper we document these changes and report the results of tests aimed at determining the causes of these physiognomical changes. We found that livestock, leporids, introduced Mediterranean forbs and agriculture account for differences in seed dispersal and survival of A. caven and P. chilensis, which can explain the documented changes in the Chilean landscape.
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    Microhabitat use by European rabbits (Oryctolagus cuniculus) in central Chile: Are adult and juvenile patterns the same?
    (1982) Simonetti, Javier A.; Fuentes, Eduardo
    Rabbits (Oryctolagus cuniculus) have been recently introduced to central Chile; adult rabbits have been previously reported to exhibit a release in their use of microhabitats due to lack of effective predation upon them. This paper shows that kittens and juvenile rabbits do not exhibit the same microhabitat use pattern as adults, in spite of the very low predation pressure upon them. These results suggest that small rabbits are ecologically comparable to native rodents.
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    Shrub clumps of the Chilean matorral vegetation: structure and possible maintenance mechanisms
    (1984) Fuentes, Eduardo; Otaiza, Ricardo D.; Alliende, M. Catalina; Hoffmann, Alicia; Poiani, Aldo
    Previous studies have claimed that the Chilean matorral is more open than the Califonia chaparral, and have attributed this dissimilarity largely to the role of man in Chile. In this paper we show that in general the Chilean matorral has a structure better described as shrub clumps that merge to form a continuous vegetation matrix only in very mesic habitats, where it is comparable to the Califonia chaparral. We also present evidence that these clumps have been present for at least the last 26 years and that even without human disturbance they are likely to maintain themselves. Evidence for the latter pertains to seed dispersal, seed germination and establishment, seedling survival, and the diameter size structure of shrub clumps. Finally, we propose that differences between the California chaparral and Chilean matorral are more profound than previously thought and are due not only to different degrees of human disturbance, but also to the presence of periodical natural fires in California and not in Chile, and to different shrub recruitment patterns and mammalian herbivore activity in the two areas.
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    Tristerix tetrandrus (Loranthaceae) and its host-plants in the Chilean matorral: patterns and mechanisms
    (1986) Hoffmann, Alicia; Fuentes, Eduardo; Cortes, Irma; Liberona, Flavia; Costa, Virginia
    Interactions between a Chilean mistletoe, quintral (Tristerix tetrandrus, Loranthaceae) and its potential host plants were studied at a site with mediterranean type climate. The results show that the distribution of T. tetrandrus is related to the behavior of avian dispersers, which feed on its fruit, and evacuate the seeds at random in the field, but the distribution is also influenced bymicroenvironmental conditions, survival of seedlings is hampered at drier locations. The infection capacity of the seeds is increased after birds have eliminated the fruit coat. Survival of T. tetrandrus seeds differed depending on the species to which they were attached experimentally. Seeds germinated, and plants developed on Colliguaya odorifera and Kageneckia oblonga, previously reported as susceptible to infection. Survival was significantly higher on C. odorifera, although in the field it is infected less frequently than K. oblonga. In species on which no T. tetrandrus has been previously reported, resistance to infection might be ascribed to different mechanisms: in Quillaja saponaria, differentiation of cork layers apparently prevents penetration by haustoria; in Lithraea caustica haustoria enter the cortex and phloem, but no further development ensues. K. oblonga seldom bears more than one T. tetrandrus plant. Experimental inoculations showed that significantly more seeds developed into plants on K. oblonga individuals not previously infected with quintral, suggesting that they become resistant to infection.Interactions between a Chilean mistletoe, quintral (Tristerix tetrandrus, Loranthaceae) and its potential host plants were studied at a site with mediterranean type climate. The results show that the distribution of T. tetrandrus is related to the behavior of avian dispersers, which feed on its fruit, and evacuate the seeds at random in the field, but the distribution is also influenced bymicroenvironmental conditions, survival of seedlings is hampered at drier locations. The infection capacity of the seeds is increased after birds have eliminated the fruit coat. Survival of T. tetrandrus seeds differed depending on the species to which they were attached experimentally. Seeds germinated, and plants developed on Colliguaya odorifera and Kageneckia oblonga, previously reported as susceptible to infection. Survival was significantly higher on C. odorifera, although in the field it is infected less frequently than K. oblonga. In species on which no T. tetrandrus has been previously reported, resistance to infection might be ascribed to different mechanisms: in Quillaja saponaria, differentiation of cork layers apparently prevents penetration by haustoria; in Lithraea caustica haustoria enter the cortex and phloem, but no further development ensues. K. oblonga seldom bears more than one T. tetrandrus plant. Experimental inoculations showed that significantly more seeds developed into plants on K. oblonga individuals not previously infected with quintral, suggesting that they become resistant to infection.Interactions between a Chilean mistletoe, quintral (Tristerix tetrandrus, Loranthaceae) and its potential host plants were studied at a site with mediterranean type climate. The results show that the distribution of T. tetrandrus is related to the behavior of avian dispersers, which feed on its fruit, and evacuate the seeds at random in the field, but the distribution is also influenced bymicroenvironmental conditions, survival of seedlings is hampered at drier locations. The infection capacity of the seeds is increased after birds have eliminated the fruit coat. Survival of T. tetrandrus seeds differed depending on the species to which they were attached experimentally. Seeds germinated, and plants developed on Colliguaya odorifera and Kageneckia oblonga, previously reported as susceptible to infection. Survival was significantly higher on C. odorifera, although in the field it is infected less frequently than K. oblonga. In species on which no T. tetrandrus has been previously reported, resistance to infection might be ascribed to different mechanisms: in Quillaja saponaria, differentiation of cork layers apparently prevents penetration by haustoria; in Lithraea caustica haustoria enter the cortex and phloem, but no further development ensues. K. oblonga seldom bears more than one T. tetrandrus plant. Experimental inoculations showed that significantly more seeds developed into plants on K. oblonga individuals not previously infected with quintral, suggesting that they become resistant to infection.
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    Vegetation change in large clearings: Patterns in the Chilean matorral
    (1986) Fuentes, Eduardo; Hoffmann, Alicia; Poiani, Aldo; Alliende, Maria C.
    Previous studies have shown that in Chile the so called mature matorral can have the form of either a continuous matrix of shrubs (wet sites) or of multispecific clumps of shrubs (dry sites). After clearing, sites are known to be initially covered by annuals and then byBaccharis spp. orAcacia caven shrubs. Further vegetation changes are still not documented. In the first part of this contribution we show evidence indicating that the ?seed rain? of plants dispersed by birds is important only around bird perches and that in general ?seed shadows? of mature matorral shrubs are small. These results suggest that late recolonization of cleared areas occurs by a slow diffusion process in which the presence of perching sites for birds plays a significant role. Then we exhibit results regarding the importance of seasonal droughts and European rabbits in explaining transitions between the various types of plant cover. Here we conclude that nursing by older shrubs and not by rocks or fallen branches, is a requirement to insure the survival of seedlings belonging to mature matorral shrubs. Nurses are important regarding both summer desiccation and herbivory. These nurse effects seem to be more important at dry sites where rabbits are also more numerous, than at wet sites where conditions seem somewhat milder and vegetation change could be faster. In the last part we discuss a scheme of vegetation change that incorporates these processes and explains the relation between them, the vegetation types and the recolonization of wet and dry areas. Finally, a brief mention is made to the difference between these processes and the comparable ones in the California chaparral.
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    Vegetative responses to defoliation of two Chilean matorral shrubs
    (1980) Torres, Juan C.; Gutiérrez, Julio R.; Fuentes, Eduardo
    This paper reports the results of experimental defoliation of two common matorral species: Lithraea caustica and Colliguaya odorifera. L. caustica and C. odorifera are the matorral species previously shown to exhibit the highest and lowest levels of natural defoliation by browsing. Experimental defoliation was performed at four levels: 0% (controls), 25%, 66%, and 100%. C. odorifera exhibited vegetative responses stronger than controls only in the two highest levels of defoliation (66% and 100%), whereas L. caustica responded vigorously at the 25% and 100% levels. The results are related to the observed position of both species in the matorral community and their relative defoliation risks by natural and introduced herbivores.