Simón Bolívar University

About: Simón Bolívar University is a education organization based out in Caracas, Venezuela. It is known for research contribution in the topics: Population & Crystallization. The organization has 5912 authors who have published 8294 publications receiving 126152 citations.

Responses to drought of five Brachiaria species. I. Biomass production, leaf growth, root distribution, water use and forage quality

Abstract: The introduction of African grasses in Neotropical savannas has been a key factor to improve pasture productivity. We compared the response of five Brachiaria species to controlled drought (DT) in terms of biomass yield and allocation, pattern of root distribution, plant water use, leaf growth, nutrient concentration and dry matter digestibility. The perennial C4 forage grasses studied were B. brizantha (CIAT 6780), B. decumbens (CIAT 606), B. dictyoneura (CIAT 6133), B. humidicola (CIAT 679) and B. mutica. Two DT periods, which mimic short dry spells frequent in the rainy season, were imposed by suspending irrigation until wilting symptoms appeared. They appeared after 14 days in B. brizantha, B. decumbens and B. mutica, and after 28 days in B. humidicola and B. dictyoneura. The impossed drought stress was mild and only the largest grass, B. brizantha, showed reduced (23%) plant yield. The other grasses were able to adjust growth and biomass allocation in response to DT leaving total plant yield relatively unaffected. Brachiaria mutica, had a homogeneous root distribution throughout the soil profile. In the other species more than 80% of root biomass was allocated within the first 30 cm of the soil profile. Brachiaria brizantha and B. decumbens had the lowest proportion of roots below 50 cm. Drought caused a general reduction in root biomass. The shoot:root ratio in B. mutica and B. humidicola increased in response to DT at the expense of a reduction in root yield down to 50 cm depth. Although the total water volume utilized under DT was similar among grasses, the rate of water use was highest (0.25 l day−1) in B. brizantha, B. decumbens and B. mutica and lowest (0.13 l day−1) in B. humidicola and B. dictyoneura. In all species leaf expansion was reduced by DT but it was rapidly reassumed after rewatering. Drought increased specific leaf mass (SLM) only in B. brizantha compensating for leaf area reduction, but leaf area ratio (LAR) was unaffected in all species. In almost all grasses DT increased leaf N and K concentration and in vitro dry matter digestibility. The results indicate that B. brizantha, B. decumbens and to a lesser extent, B. mutica are better adapted to short dry periods, whereas B. humidicola and B. dictyoneura are better adapted to longer dry periods.

Growth rate variation among passerine species in tropical and temperate sites: an antagonistic interaction between parental food provisioning and nest predation risk

Abstract: Causes of interspecific variation in growth rates within and among geographic regions remain poorly understood Passerine birds represent an intriguing case because differing theories yield the possibility of an antagonistic interaction between nest predation risk and food delivery rates on evolution of growth rates We test this possibility among 64 Passerine species studied on three continents, including tropical and north and south temperate latitudes Growth rates increased strongly with nestling predation rates within, but not between, sites The importance of nest predation was further emphasized by revealing hidden allometric scaling effects Nestling predation risk also was associated with reduced total feeding rates and per-nestling feeding rates within each site Consequently, faster growth rates were associated with decreased per-nestling food delivery rates across species, both within and among regions These relationships suggest that Passerines can evolve growth strategies in response to predation risk whereby food resources are not the primary limit on growth rate differences among species In contrast, reaction norms of growth rate relative to brood size suggest that food may limit growth rates within species in temperate, but not tropical, regions Results here provide new insight into evolution of growth strategies relative to predation risk and food within and among species

Chemical ecology of the palm weevil Rhynchophorus palmarum (L.) (Coleoptera: Curculionidae): Attraction to host plants and to a male-produced aggregation pheromone

Abstract: Attraction to host plants by adultRhynchophorus palmarum (L.) palm weevils was studied in the field and in the laboratory. Chemical analysis revealed the presence of ethanol and ethyl-acetate in stems of coco palms and in pineapple fruits and of pentane, hexanal, and isopentanol in coco stems. In the olfactometer, the first two compounds and isoamyl-acetate were attractive to the insects and the last three compounds, although not attractive by themselves, increased attractiveness when mixed with the first two compounds. Mixtures of these compounds, in proportions similar to the one occurring in attractive plant tissue, were as attractive as natural coconut tissue. In the field, the chemical compounds, either presented alone or as a mixture, did not attract the weevil. Males produce an aggregation pheromone when smelling ethyl-acetate. Rhynchophorol, 2(E)-6-methyl-2-hepten-4-ol, the known active component of the aggregation pheromone, attracts weevils in the olfactometer and in the field only if plant tissue, ethyl-acetate, or the above-mentioned odor mix are present. We propose that a complex mix of ethanol, ethyl-acetate, pentane, hexanal, isolamyl-acetate, and/or isopentanol serve as a short-range orientation cue to fresh wounds on the plant and that additional host odors, attracting weevils from a distance, have still to be discovered. Rhynchophorol can be considered to be a Synergist, having an anemotactic action at a distance. We recommend the use of retention traps baited with rhynchophorol, ethyl-acetate, and sugar cane as an alternative control method for the pest.