enero - junio 2009 http://www.saber.ula.ve/handle/123456789/30059 2026-04-26T10:14:37Z 2026-04-26T10:14:37Z - http://www.saber.ula.ve/handle/123456789/31064 2018-03-15T01:45:55Z 2010-05-20T15:20:56Z

Resúmenes de tesis -

2010-05-20T15:20:56Z Gamboa, Maribet Chacón, Marleny Segnini, Samuel http://www.saber.ula.ve/handle/123456789/30063 2018-03-15T01:45:34Z 2009-12-08T12:24:52Z

Ritmo diario de alimentación y tamaño de presa en cuatro especies simpátricas de plecoptera (insecta) en un río tropical andino Gamboa, Maribet; Chacón, Marleny; Segnini, Samuel Se comparó la actividad diaria de alimentación y el tamaño de presas consumidas por las ninfas de Plecoptera de Anacroneuria chorrera, A. cacute, A. paleta y A. tachira, especies que viven en simpatría en el río La Picón en Mérida, Venezuela. Se tomaron muestras del fondo del río cada cuatro horas en tres ciclos de 24 horas. De cada muestra se seleccionaron las ninfas maduras de Plecoptera. A cada ninfa se le midió el ancho cefálico y se analizó su contenido estomacal para determinar la condición de llenura del estómago y estimar el tamaño promedio de las presas consumidas. Los resultados de llenura estomacal muestran que las cuatro especies se alimentaron constantemente durante 24 horas diarias, aunque dos de ellas, A. tachira y A. paleta, exhibieron cierto grado de periodicidad en el ritmo diario de alimentación. El tamaño de las presas ingeridas estuvo asociado al tamaño de las ninfas de las cuatro especies. Las ninfas de mayor tamaño (A. chorrera) consumieron las presas más grandes y las ninfas de menor tamaño (A. paleta) se alimentaron de las presas más pequeñas. Las especies A. tachira y A. cacute, con tamaños intermedios entre las dos especies anteriores, se alimentaron de presas con tallas también intermedias. Se concluye que tanto la actividad diaria de alimentación y el tamaño de las presas consumidas contribuyen a la separación del nicho trófico de las cuatro especies de Plecoptera presentes en el río La Picón.

2009-12-08T12:24:52Z Schwarzkopf Kratzer, Teresa Trevisan, María Cristina Silva Armas, Juan F. http://www.saber.ula.ve/handle/123456789/30062 2018-03-15T01:45:33Z 2009-12-08T12:20:36Z

A matrix model for the population dynamics of Hyptis suaveolens, an annual weed Schwarzkopf Kratzer, Teresa; Trevisan, María Cristina; Silva Armas, Juan F. Hyptis suaveolens is a neotropical annual weed that invades savanna agricultural systems. Although fire, grazing and soil disturbances have been proposed to cause its local dominance, these factors have not been experimentally tested. A field experiment was carried out in a savanna in the Venezuelan Llanos. Six treatments were meant to simulate proposed disturbances and explore underlying causes of the species’ local dominance. A matrix population model was developed and for each treatment demographic and perturbation analyses were performed. Results indicate that population growth rate is promoted by all simulated disturbances but fire and nearby vegetation removal, increasing with disturbance intensity, especially under plowing. Demographic analyses show that the increase in population growth rate is mainly due to fecundity. However, germination is the most sensitive parameter. Fire and digging produced a strong reduction in germination, although this negative contribution is smaller than the positive contribution made by fecundity in the digging treatment. Matrix population model analyses allowed a better understanding of the processes leading to increases in the weed’s growth rate, and allow development of more effective control measures. Some of them include avoiding soil disturbance and increasing control over germination. We also discuss the constraints of the developed model.

2009-12-08T12:20:36Z Díaz Díaz, Oscar Liñero Arana, Ildefonso Villafranca, Siolíz Allen, Thays http://www.saber.ula.ve/handle/123456789/30061 2018-03-15T01:45:32Z 2009-12-08T12:15:31Z

Epizoic polychaetes (annelida: polychaeta) on Crassostrea rhizhophorae (guilding, 1828) from la restinga lagoon, Margarita island, Venezuela Díaz Díaz, Oscar; Liñero Arana, Ildefonso; Villafranca, Siolíz; Allen, Thays Species richness of epizoic polychaetes on the mangrove oyster, Crassostrea rhizophorae (Guilding 1828), was studied. Monthly collections (January-August, 2001) were made. Oysters were separated from mangroves roots by hand in La Restinga lagoon and put into plastic bags with seawater, taken to the laboratory and placed in aquariua. Two hundred and forty five oysters were examined, having 1229 polychaetes belonging to 56 species. The biogeographic composition of the species allows some grouping as cosmopolitan (32.3%), Atlantic Ocean (23.3%), amphiamericans (18.6%), pantropical (9.3%) and disjunct species (2.3%).

2009-12-08T12:15:31Z Valois Cuesta, Hamleth López Perea, Diana Y. Quinto Valoyes, Zulay http://www.saber.ula.ve/handle/123456789/30060 2018-03-15T01:45:30Z 2009-12-08T12:07:28Z

Reproductive ecology of Psychotria poeppigiana (RUBIACEAE): a comparative analysis between long-styled and short-styled plants Valois Cuesta, Hamleth; López Perea, Diana Y.; Quinto Valoyes, Zulay We investigate morph-specific patterns in flower morphology, nectar concentration, and foraging behavior of flower visitors in a population of Psychotria poeppigiana (Rubiaceae), a distylous species of secondary forests in the Chocó, Colombia. The studied population had 1:1 ratio between morphs. We did not observe strict reciprocity in the position of stigma and anthers between short-styled and long-styled flowers, since the space separation between anther and stigma was greater in long-styled flowers. We did not observe differences between floral morphs in flowering and fruiting patterns. Nectar concentration was not different between floral morphs throughout the day. The relation between nectar concentration and floral visits experienced by plants of both morphs was evident. Trigona spinipes (bees) was the most frequent floral visitor of P. poeppigiana. However, Phaethornis striigularis (hummingbird) and Heliconius erato venus (butterfly) probably are more effectives as pollinators. Our results suggest that floral morphs of P. poeppigiana don’t presented reproductive conflicts or functional gender specialization based on the manifestation of reproductive phenology, patterns of nectar concentration, and floral visits.

2009-12-08T12:07:28Z