Showing papers by "University of Costa Rica published in 1975"

Innate Recognition of Coral Snake Pattern by a Possible Avian Predator

Abstract: Inexperienced hand-reared motmots avoided a pattern of red and yellow rings but readily attacked a pattern of green and blue rings and also one of red and yellow stripes. The motmots' avoidance of the "coral snake%" pattern indicates that mimic snake species can derive protection from some potential predators.

Efecto de la ceniza del Volcán: Irazú (Costa Rica) en algunos insectos

Abstract: A study of the 1963-1965 eruptions of the Irazu volcano (Costa Rica) showed that the ashes altered the ecological conditions of a great number of insects. Experiments suggest a mechanical action of the abrasive particles on the epicuticle, making it permeable, and thus accelerating dehydration. Other insects, such as the honey bee (Apis mellifera), were not affected externally but through the ingestion of ash-contaminated nectar and by the massive destruction of the vegetation on which they depended. Great destruction of bee populations was observed during 1964 and 1965-66 in the San Jose area. On the other hand, the volcanic ash apparently favored other insects, especially those protected by a waxy secretion, and by the possible elimination of their natural enemies, to such proportions that they became pests of economic significance.

Algunos aspectos de anatomía foliar comparada de dos especies de Bromeliaceae (Aechmea mexicana Baker y Hechtia glomerata Zucc.)

Abstract: The leaf anatomy of two Bromeliaceae, Hechtia glomerata Zucc., a terrestrial xerophyte of arid zones, and Aechmea mexicana Baker, a tropical moist forest epiphyte, is compared; these species show adaptations to different extremes of adverse environmental conditions as to water uptake. The leaves of A. mexicana have more water storage tissue than those of H. glomerata; on the other hand, H. glomerata is capable of root absorption. In A. mexicana, modified nonfunctional stomata increase transpiration resistance. Also, this species shows more specialized foliar trichomes which permit the uptake of water and possibly of nutrients. The balance between transpiration and absorption rates is regulated in both species by the combined presence of peltate scales and stomata. The degree of adaptation to drought presented by epiphytic species is more complicated than that shown by terrestrial species. Epiphytic plants like A. mexicana may be derived from xerophytic species that have undergone readaptation to a humid climate. The conspicuous negative geotropism in the leaves of A. mexicana causes the formation of basal deposits of water, which play an important functional role in survival.

Descripción de un método simple y económico para el estudio de cariotipos en serpientes

Abstract: We describe a method for the preparation of snake chromosomes in metaphase, based on the in vivo stimulation of leucocytes with crude phytohemagglutinin from Phaseolus lunatus and the in vitro blocking of mitosis with colchicine. It has the advantage of preserving the specimen alive without the complications of cell culture, and can be performed under field conditions.

Formas en la tenencia de la tierra en Costa Rica durante el régimen colonial

Abstract: Introduccion El territorio actual de Costa Rica comprende alrededor de cincuenta mil kilometros cuadrados de superficie y dentro de el es posible hallar diversas condiciones ecologicas. Predominan las llanuras humedas y calidas en la region oriental y el sureste y mas al norte, o sea en las margenes meridionales del Lago de Nicaragua y la ribera derecha del rio San Juan. Son calidas y secas durante parte del ano, las del noroeste, que comprende la actual provincia de Guanacaste y el area oriental del Golfo de Nicoya. El Valle Central ocupa una depresion estructural divergente, y se caracteriza por su clima templado; hay en las marcadas diferencias que son el resultado de las influencias oceanicas. Por el este son las que provienen del Caribe; las del oeste del Pacifico. No en vano ha dejado senalado el sabio Pittier, que el clima general de pais es maritimo mas que continental, como resultado de hallarse dentro de la franja istmica del continente americano.