Browsing by Author "Jaksic, F. M."

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    Ecological efficiency and legitimacy in seed dispersal of an endemic shrub (Lithrea caustica) by the European rabbit (Oryctol gus cuniculus) in central Chile
    (2008) Castro, S. A.; Bozinovic, F.; Jaksic, F. M.
    The European rabbit (Oryctolagus cuniculus) is an alien herbivore in central Chile. Although its diet is poorly studied, this rabbit is known to consume native fruits and seeds, and thus it could act as a seed-dispersal agent. We evaluated the effect of endozoochory by rabbits on the survival and germination of seeds of a native shrub (Lithrea caustica, Anacardiaceae), as well as its consequences for seed dispersal. We extracted seeds by hand from parental shrubs, and compared the germination dynamics of seeds passing once and twice throughout the rabbit's gut (simulating its coprophagy) versus control treatments (seeds not consumed). Additionally, in permanent 2 x 2 m sampling plots placed in the wild, we evaluated the abundance of L. caustica seedlings and of its seeds in rabbit droppings. Results indicate that rabbits reduced seed survival to 82% on average with the first gut passage, and to an additional 52% with a second passage. Nevertheless, germination variables such as initiation time and germination, as well as final germination rate, increased significantly in comparison to non-ingested seeds. Sampling plots showed that L. caustica seedlings were concentrated principally underneath woody patches, which are then regarded as safe sites. Outside shrub cover, seedling abundance small, this indicates that open places are unsafe sites. We recorded that feces (and seeds contained) were deposited in higher proportion beneath woody cover, Thus, the native shrub L. caustica may be dispersed by alien rabbits through endozoochory, which provides legitimacy and efficiency in this dispersal service. Alien rabbits may fill a similar role played by native mammals, which have been reduced in abundance by human agency in central Chile. We suggest that the generalist syndrome, common among plants and dispersers, may be an arena of positive effects in ecological interactions between alien and native species. (c) 2008 Published by Elsevier Ltd.
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    ENSO-associated response of field urine osmolality in the insectivorous marsupial Thylamys elegans
    (2008) Tirado, C.; Cortes, A.; Jaksic, F. M.; Bozinovic, F.
    From 1991 to 1994, we assessed physiological responses in field urine osmolality (Uosm) of an insectivorous marsupial (Thylamys elegans) of semiarid Chile faced with a complete cycle of El Nino Southern Oscillation (ENSO). El Nino phase of ENSO determined the initial 2 wet years at the Study site. while La Nina phase determined the 2 subsequent dry years. The marsupial showed marked temporal fluctuations in field Uosm values, with both seasonal and between-year patterns of physiological variability. Indeed, Uosm values during wet years were: 2.719 +/- 405mOsm/kg in summer versus 2.246+209mOsm/kg in winter. During dry years in summer, Uosm values were: 3.340 +/- 384 mOsm/kg versus 2.481+293mOsm/kg during winter. There were significant effects of dry versus wet years and between dry and wet seasons on Uosm values, as well as a statistical interaction year x season. We discuss how the integration of flexible physiological mechanisms enable an insectivorous marsupial to cope with seasonal and yearly water variability in a semidesert, and also the importance of using ENSO climate effects as a proxy for the study of future climate change in natural Communities and its subsequent impact on field physiological performance of desert mammals. (c) 2008 Elsevier Ltd. All rights reserved.