Photosynthetically active radiation and carbon gain drives the southern orientation of Myrtillocactus geometrizans fruits.

The equatorial orientation of reproductive structures is known in some columnar cacti from extratropical deserts. It has been hypothesised that photosynthetically active radiation (PAR) interception is the main reason for this orientation, because of its key effect on nocturnal CO2 uptake. However, there are no studies addressing both the effect of PAR and its consequence, carbon gain, on fruit orientation. Accordingly, we tested whether PAR and carbon gain could explain the southern fruit orientation of Myrtillocactus geometrizans, an inter-tropical columnar cactus. We studied three populations of M. geometrizans in Mexico. For each population, azimuth of fruits, total daily PAR, nocturnal acid accumulation (NAA) and fruit production were measured. The relationships between rib orientation and number of fruits, as well as total daily PAR, were evaluated using periodic regressions. The effect of total daily PAR and NAA on number of fruits was assessed using generalised linear models. During spring, mean fruit orientation had a south azimuth for three populations. Likewise, rib orientation had a significant effect on fruit production, with the south-facing ribs having the maximum number of fruits. Total daily PAR was highest in the south-facing ribs, at least for those in the northern and central populations. Furthermore, during spring, there was a significant positive effect of total daily PAR and NAA on fruit production. Our results provide strong evidence that the higher carbon gain in equatorial ribs, through a highest interception of PAR, would be the responsible factor for equatorial orientation of fruits in an inter-tropical columnar cactus.

Diversidad de escarabajos necrófilos (Coleoptera: Scarabaeidae, Silphidae, Staphylinidae y Trogidae) en una región semiárida del valle de Zapotitlán de las Salinas, Puebla, México / Necrophilous beetles diversity (Coleoptera: Scarabaeidae, Silphidae, Staphylinidae and Trogidae) in a semiarid area of Zapotitlán de las Salinas valley, Puebla, Mexico

Mexico is constituted of arid and semiarid areas in more than half of its land extension, where most of their resources are available only during the rainy season. For those species that recycle resources, such as the carrion fauna, this represents a highly active season; however, the biological and diversity patterns of carrion fauna are poorly understood in these areas. Here, we studied the abundance, diversity and richness of the Scarabaeidae, Silphidae, Staphylinidae and Trogidae families in the Zapotitlán de las Salinas Valley in Puebla, Mexico. Over a one-year period, monthly samples were collected from five different vegetation systems that included the scrublands, a columnar cactus landscape, and altered vegetation. Samples were collected with the use of NTP-80 traps baited with squid, and data on abundance and richness were obtained and evaluated, with respect to monthly precipitation and sampling site location. We collected a total of 613 insects from 12 genera and 15 species. Across systems, Staphylinidae showed the greatest richness (nine species) and abundance (74.2%), followed by Scarabaeidae (21.9%), Silphidae (2.9%) and Trogidae (1%). Significant differences were observed between sites and months; nevertheless, no relationship was observed between abundance and temperature or precipitation. Across taxonomic groups, abundance and richness were most evident for scrub sites, while a greater abundance during the dry season was obtained. The results of this study indicated that the carrion faunal community composition is closely related to the type of vegetation and did not depend on the rainy season. In spite that lesser carrion fauna was observed in this area when compared to other regions of Mexico, this report constitutes a significant contribution to our understanding of the ecological role of this fauna in arid areas.

Las zonas áridas y semiáridas ocupan más de la mitad del territorio de México, sin embargo, son ambientes donde los escarabajos necrófilos han sido escasamente estudiados. En esta investigación se presenta la diversidad y fenología de Scarabaeidae, Silphidae, Staphylinidae y Trogidae en el valle de Zapotitlán de las Salinas, Puebla. Se realizaron muestreos mensuales durante un año de abril de 1998 a marzo de 1999 empleando trampas tipo NTP-80 cebadas con calamar, distribuidas en un mezquital y matorral espinoso, en cactáceas columnares y vegetación alterada. Se capturaron 613 individuos de 12 géneros y 15 especies. Staphylinidae tuvo la mayor riqueza (9 especies) y abundancia (74.2%), le siguieron Scarabaeidae (21.9%), Silphidae (2.9%) y Trogidae (1%) con dos especies cada una. La fauna para las dos primeras fue inferior a la observada en otras zonas de México. La máxima abundancia y riqueza estuvieron en la época seca y las comunidades de escarabajos necrófilos prefirieron los sitios con mezquital y matorral, donde permanecieron más tiempo y se registraron todas las especies, por lo tanto los tipos de vegetación presentes fueron el factor más importante que determinó las variaciones locales de abundancia, diversidad y riqueza y no la época de lluvias.

Factors affecting establishment success of the endangered Caribbean cactus Harrisia portoricensis (Cactaceae)

Early plant stages may be the most vulnerable within the life cycle of plants especially in arid ecosystems. Interference from exotic species may exacerbate this condition. We evaluated germination, seedling survival and growth in the endangered Caribbean cactus Harrisia portoricensis, as a function of sunlight exposure (i.e., growing under open and shaded areas), different shade providers (i.e., growing under two native shrubs and one exotic grass species), two levels of predation (i.e., exclusion and non-exclusion) and variable microenvironmental conditions (i.e., temperature, PAR, humidity). Field experiments demonstrated that suitable conditions for germination and establishment of H. portoricensis seedling are optimal in shaded areas beneath the canopy of established species, but experiments also demonstrated that the identity of the shade provider can have a significant influence on the outcome of these processes. Harrisia portoricensis seedlings had higher probabilities of survival and grew better (i.e., larger diameters) when they were transplanted beneath the canopy of native shrubs, than beneath the exotic grass species, where temperature and solar radiation values were on average much higher than those obtained under the canopies of native shrubs. We also detected that exclusión from potential predators did not increase seedling survival. Our combined results for H. portoricensis suggested that the modification of microenvironmental conditions by the exotic grass may lower the probability of recruitment and establishment of this endangered cactus species. Rev. Biol. Trop. 60 (2): 867-879. Epub 2012 June 01.

Las etapas iniciales de las plantas parecen ser las más vulnerables de su ciclo de vida, especialmente en ecosistemas áridos. Interferencias de especies exóticas pueden exacerbar esta condición. Evaluamos la germinación, supervivencia y crecimiento de plántulas del cactus en peligro de extinción Harrisia portoricensis, en función de la exposición a la luz solar, diferentes proveedores de sombra, exclusión de potenciales depredadores y condiciones micro-ambientales variables. Los experimentos demostraron que las condiciones adecuadas para la germinación y el establecimiento de plántulas de H. portoricensis son óptimas en áreas de sombra, bajo el dosel de especies establecidas, pero también demostraron que la identidad de los proveedores de sombra puede tener una influencia significativa sobre los resultados de estos procesos y que la exclusión de depredadores no aumentó la probabilidad de supervivencia de las plántulas. Las plántulas de H. portoricensis tuvieron mayores probabilidades de supervivencia y crecieron mejor cuando fueron transplantadas bajo la sombra de los arbustos nativos que bajo la sombra del pasto exótico, donde la temperatura y la radiación solar fueron en promedio mucho mayores que las obtenidas bajo la sombra de los arbustos nativos. Nuestros resultados sugieren que las modificaciones de las condiciones micro-ambientales por este pasto exótico pueden disminuir la probabilidad de reclutamiento y establecimiento de esta especie en peligro.

Preliminary notes on yeasts associated with necrotic cactus stems from different localities in Brazil

The yeast species found in necrotic stems of three columnar cacti (Pilosocereus machrisii, Pilosocereus vilaboensis, and Praecereus euchlorus)at eight localities in Brazil were described and a similarity analysis using Sorensen distances was used to compare the composition of yeast species at these localities. Of 56 necrotic cactus stems sampled,32 produced yeast colonies. Ten species of yeast or yeast-like microorganisms were identified from 53 isolates, with Pichia cactophila, Candida sonorensis, Geotrichum sp., and Sporopachydermia cereana being the most common. The remaining species occurred in low proportions in the cacti surveyed. The similarity analysis provided a dendogram (UPGMA) that clustered the yeast communities from different cactus species and indicated that host cactus species was unimportant in this clustering.

As leveduras encontradas em cladódios necrosados de três cactos colunares (Pilosocereus machrisii, Pilosocereus vilaboensis and Praecereus euchlorus) em oito localidades no Brasil foram identificadas e uma análise de similaridade baseada na distância Sorensen foi usada para comparar as comunidades nas diferentes localidades. Dos 56 cladódios necrosados amostrados, 32 produziram colônias de leveduras. Dez espécies de leveduras foram identificadas a partir de 53 isolados, com as espécies Pichia cactophila, Candida sonorensis, Geotrichum sp. e Sporopachydermia cereana sendo as mais comuns. As espécies restantes ocorreram em baixas freqüências. O dendograma (UPGMA) construído a partir da análise de similaridade agrupou comunidades de leveduras obtidas em diferentes espécies de cactos e indicou que as espécies de cactos hospedeiros não foram determinantes nesse agrupamento.