Estudio del oso andino (Tremarctos ornatus) como dispersor legítimo de semillas y elementos de su dieta en la región de Apolobamba-Bolivia
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Ecología en Bolivia
Abstract
Poco se conoce aun sobre la ecología del oso andino y el rol que cumple en los ecosistemas que habita. Este trabajo pretende contribuir al conocimiento sobre su ecología evaluando la legitimidad del oso andino como dispersor de semillas y conocer elementos de su dieta alimenticia en la región de estudio. Entre los meses de julio y octubre en 1998 y abril y junio en 1999, se recolectaron heces y otros rastros de alimentación así como semillas de las plantas. Para estimar el efecto de la ingesta se realizaron pruebas de germinación y de viabilidad. Los resultados sugieren que el oso andino es un agente dispersor legítimo de tres especies de plantas: Nectandra cf. cuneatocordata, Symplocos cf. cernua y Gaultheria vaccinioides. Sus semillas se encontraron ilesas y viables después de haber sido ingeridas. Las semillas de Gaultheria vaccinioides consumidas por el oso, germinaron en un porcentaje y tiempo similar a las muestras control. De igual forma, el porcentaje de viabilidad de las semillas de Symplocos cf. cernua no mostraron diferencias entre heces y frutos. En el caso de las semillas de Nectandra cf. cuneatocordata el porcentaje de germinaci ón fue similar a las muestras control, sin embargo las semillas ingeridas germinaron en menor tiempo. Los frutos de Gaultheria vaccinioides fueron consumidos en la zona de estudio también por otros animales como aves y zorro andino (Pseudalopex culpaeus). Comparando la germinación de las semillas de las heces de estos animales con las del oso, se encontró que no existían diferencias en el porcentaje de germinación pero sí en la rapidez. Las semillas consumidas por el oso y zorro germinaron en menos tiempo que aquellas consumidas por las aves. A partir del análisis de heces y de otros rastros indirectos de alimentación, la dieta del oso andino para la región de Apolobamba en términos de frecuencia consta en un 57,5% de especies de la familia Bromeliaceae: Puya atra, Puya sp., Tillandsia rubella; en un 34,8 % por frutos de Gaultheria vaccinioides, Symplocos cf. cernua y Nectandra cf. cuneatocordata; en 7,5% se observó el consumo de ganado (Bos taurus y Equs caballus) y en 1,5 % de aves.
Little is know on Andean bear ecology and the role that this species could play in the ecosystems in which it is found. The objective of this study is to increase ecological knowledge of this species by evaluating if the Andean bear is a legitimate seed disperser and examining its dietary elements. During July and October of 1988 and April and June of 1999, seeds, plants and Andean bear feces were collected. To determine the effects of ingestion, seed germination and viability were tested. The results suggest that Andean bear is a legitimate dispersing agent of three species of plants: Nectandra cf. cuneatocordata, Symplocos cf. cernua, and Gaultheria vaccinioides, since their seeds were found unharmed and viable after having passed through the bear's digestive tract. The seeds from Gaultheria vaccinioides that were consumed by the bear germinated in a similar percentage and time to those of test samples. Likewise, the percentage of viability in Symplocos cf. cernua seeds did not show any differences between those found in feces and those collected from ripe fruits. In the case of Nectandra cf. cuneatocordata seeds the percentage germination was similar to the test samples, but the time for germination of seeds that were extracted from the feces was significantly shorter. The fruits of Gaultheria vaccinioides were also consumed in the study zone by other animals such as birds and Andean foxes (Pseudalopex culpaeus). Comparing the germination of seeds from the fecal samples of these animals with those of bears, it was found that there was no difference in the percentage of germination, but there was in the speed. The seeds consumed by bears and foxes germinated in less time than those consumed by birds. Based on the feces analysis and other indirect food traces, the Andean bear's diet in the Apolobamba region in terms of frequency of occurrence consists of 57.5% species from the Bromeliaceae family: Puya atra, Puya sp., Tillandsia rubella; 34.8 % of Gaultheria vaccinioides, Symplocos cf. cernua and Nectandra cf. cuneatocordata fruits; 7.5% of cattle (Bos taurus and Equs caballus), and 1.5 % of birds.
Little is know on Andean bear ecology and the role that this species could play in the ecosystems in which it is found. The objective of this study is to increase ecological knowledge of this species by evaluating if the Andean bear is a legitimate seed disperser and examining its dietary elements. During July and October of 1988 and April and June of 1999, seeds, plants and Andean bear feces were collected. To determine the effects of ingestion, seed germination and viability were tested. The results suggest that Andean bear is a legitimate dispersing agent of three species of plants: Nectandra cf. cuneatocordata, Symplocos cf. cernua, and Gaultheria vaccinioides, since their seeds were found unharmed and viable after having passed through the bear's digestive tract. The seeds from Gaultheria vaccinioides that were consumed by the bear germinated in a similar percentage and time to those of test samples. Likewise, the percentage of viability in Symplocos cf. cernua seeds did not show any differences between those found in feces and those collected from ripe fruits. In the case of Nectandra cf. cuneatocordata seeds the percentage germination was similar to the test samples, but the time for germination of seeds that were extracted from the feces was significantly shorter. The fruits of Gaultheria vaccinioides were also consumed in the study zone by other animals such as birds and Andean foxes (Pseudalopex culpaeus). Comparing the germination of seeds from the fecal samples of these animals with those of bears, it was found that there was no difference in the percentage of germination, but there was in the speed. The seeds consumed by bears and foxes germinated in less time than those consumed by birds. Based on the feces analysis and other indirect food traces, the Andean bear's diet in the Apolobamba region in terms of frequency of occurrence consists of 57.5% species from the Bromeliaceae family: Puya atra, Puya sp., Tillandsia rubella; 34.8 % of Gaultheria vaccinioides, Symplocos cf. cernua and Nectandra cf. cuneatocordata fruits; 7.5% of cattle (Bos taurus and Equs caballus), and 1.5 % of birds.
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Vol. 43, No. 1