Luis Hernández-Sandoval

Management and Extraction of Lippia graveolens in the Arid Lands of Queretaro, Mexico

Posgrado en Ciencias Biologicas, Universidad Nacional Autonoma de Mexico, Mexico D.F., Mexico Semidesierto de Penamiller Asociacion Rural de Interes Colectivo, Queretaro, Mexico Facultad de Ciencias Naturales, Escuela de Biologia, Universidad Autonoma de Queretaro, Queretaro, Mexico Laboratorio de Ecologia de Restauracion, Centro de Investigaciones en Ecosistemas, Universidad Nacional Autonoma de Mexico, Morelia( Michoacan, Mexico *Corresponding author; e-mail: rlindig@oikos.unam.mx

Hybrid corrosion‐resistant coatings analyzed using electrochemical noise

Purpose – The purpose of this paper is to study the corrosion of carbon steel without coating and when protected using three different hybrid coatings, i.e. a bi‐component polyurethane with nano‐particles of SiO2 with and without sacrificial anode particles, and a mono‐component polyurethane with SiO2 particles.Design/methodology/approach – In this investigation three different nano‐structured coatings are developed and applied to steel substrates and then tested for their corrosion resistance (defined as “Rn”), under a very aggressive medium (pH=1.5) in a dynamic system (loop reactor). Their performance is evaluated using an electrochemical noise (EN) resistance technique. The electrodes are connected to a potentiostat and measurements are recorded as per the EN technique over a 2,048 s duration at 0, 24, and 48 h intervals. Scanning electron microscopy (SEM) are obtained before and after the corrosion trials to characterize the control and the different coating systems.Findings – The results show that a...

A measure of regularity for polygonal mosaics in biological systems

BackgroundThe quantification of the spatial order of biological patterns or mosaics provides useful information as many properties are determined by the spatial distribution of their constituent elements. These are usually characterised by methods based on nearest neighbours distances, by the number of sides of cells, or by angles defined by the adjacent cells.MethodsA measure of regularity in polygonal mosaics of different kinds in biological systems is proposed. It is based on the condition of eutacticity, expressed in terms of eutactic stars, which is closely related to regularity of polytopes. Thus it constitutes a natural measure of regularity. The proposed measure is tested with numerical and real data. Numerically is tested with a hexagonal lattice that is distorted progressively and with a non-periodic regular tiling. With real data, the distribution of oak trees in forests from three locations in the State of Querétaro, Mexico, and the spiral pattern of florets in a flowering plant are characterised.ResultsThe proposed measure performs well and as expected while tested with a numerical experiment, as well as when applied to a known non-periodic tiling of the plane. Concerning real data, the measure is sensitive to the degree of perturbation observed in the distribution of oak trees and detects high regularity in a phyllotactic pattern studied.ConclusionsThe measure here proposed has a clear geometrical meaning, establishing what regularity means, and constitute an advantageous general purposes alternative to analyse spatial distributions, capable to indicate the degree of regularity of a mosaic or an array of points.

Beaucarnea sanctomariana (Nolinaceae), a New Micro-Endemic Species of Ponytail Palm from the Isthmus of Tehuantepec, Oaxaca, Mexico

A new species of ponytail palm, Beau- carnea sanctomariana (Nolinaceae), is described and illustrated. With this addition, the neotropical genus Beaucarnea now has 10 species. It occurs in tropical deciduous forests in the biodiversity hot- spot area known as the Chimalapas in the Tehuan- tepec Isthmus, Oaxaca, Mexico. The new taxon is similar to Beaucarnea recurvata Lemaire and to Beaucarnea hiriartiae L. Hernindez, but differs from both in its smaller flowers and fruits (the smallest in the entire genus), and in the articulation of the pedicel in both staminate and pistillate flow- ers. In addition, B. sanctomariana differs from B. recurvata in the smaller trunk bases without but- tresses, shorter leaves, and undulate bracts of the inflorescence, and from B. hiriartiae in having widely conical trunk bases, rugose bark, smooth leaf surface, larger inflorescence stalks, and shorter inflorescence branches. A discussion of field char- acters is presented.

Chronic Disturbance Affects the Demography and Population Structure of Beaucarnea inermis, a Threatened Species Endemic to Mexico:

Beaucarnea inermis is a threatened plant of the seasonally dry tropical forests of the northeastern Sierra Madre Oriental mountains. It has been affected by habitat loss and fragmentation, mainly from changes in land use and poaching. The number of B. inermis plants, sexual proportion, and structural parameters were recorded in natural populations inside the Sierra del Abra Tanchipa Biosphere Reserve and unprotected sites. Effects of chronic disturbance on demography parameters and asymmetry coefficient were estimated. Average population density is 280 ind*ha−1 inside the protected area and 186 ind*ha−1 in unprotected sites. Life tables indicate a high seedling to juvenile mortality rate, but life expectancy increases in juveniles, suggesting a survival type III curve. Population size distribution skewness indicates differences associated with disturbance. Sex ratio was 0.93:1 (m:f) inside the protected area and 0.76:1 (m:f) in unprotected sites. Anthropogenic disturbance affects life expectancy and the survival and mortality rates mainly in early life classes; however, once the adult stage is reached, mortality rate is reduced and survival rate increases. The natural protected area represents a refuge for the species from the effects of anthropogenic disturbance and illegal poaching. Additional studies are needed to evaluate the genetic diversity in B. inermis in protected and unprotected sites, and how it is affected by disturbance. Also, it is important to highlight other species inside the protected area such as Dioon edule, Zamia fischeri, and Stanhopea tigrina, which are considered as endangered or threatened.

Epiphytic Mosses in the Humid Mountain Forests of the Sierra Madre Oriental, Mexico — Species Richness, Rarity and Composition

Abstract The Humid Mountain Forests of Mexico (HMFs) harbor high species diversity and are subject to continuous fragmentation and disturbance. We inventoried the epiphytic mosses in forest fragments and on isolated trees located in the Eastern Sierra Madre (Sierra Madre Oriental). We determined the size and canopy openness of 60 trees and recorded the occurrence of epiphytic mosses on trunks. Ninety-three species and five varieties of mosses were detected, distributed among 61 genera and 26 families. Thirty-two moss taxa were strictly epiphytic and 61 were facultative. Eighteen percent (17 species) of all recorded species were rare and only 3% (3 species) were common. Nineteen genera of phorophytes were sampled. Quercus had the highest epiphytic richness. Species richness and epiphytic mosses assemblages differ between forest fragments and isolated trees. Canopy openness and mean host tree height determine the epiphytic moss richness and species assemblages. Our study further underlines the importance of the Mexican HMFs as a reservoir of epiphytic mosses.

Agave doctorensis (Agavaceae), a new species from Sierra El Doctor, Querétaro, Mexico

Agave doctorensis, a new species from Sierra El Doctor, Querétaro, Mexico is described and illustrated. It is similar to Agave montium-sancticaroli but differs in having a dense, conical panicle; reflexed bracts; and filaments inserted at two levels. The new species occurs in rosette scrub and Juniperus forest.ResumenSe describe e ilustra Agave doctorensis, una especie nueva de la Sierra El Doctor en Querétaro, México. Es similar a Agave montium-sancticaroli, pero con panículas densas, cónicas, brácteas reflejas y filamentos insertos en dos niveles. Crece en matorral rosetófilo y bosque de Juniperus.

Foliar anatomy of Beaucarnea Lemaire (Nolinaceae ss)

Beaucarnea (Nolinaceae) is a Mexican and Guatemalan genus that inhabits dry tropical areas. Most of the species are endangered under the Mexican legislation because they have a high horticultural demand and are threatened by habitat destruction. Species are difficult to recognize, since their differences are a mixture of trunk, inflorescence and fruit characters frequently absent in herbarium specimens. The aim of this work is to describe the foliar anatomy of the 11 species of Beaucarnea in search of characters with taxonomic value to sustain the generic subdivision, and to provide a key for specimens determination based on leaf and growth form. We found that four species (B. compacta, B. gracilis, B. purpusii and B. stricta) have a grooved leaf outline in transverse section, whereas the rest of the species are undulated. Other characters, such as epicuticular waxes, stomatal distribution and density, marginal teeth length and leaf apex provide valuable characters for species determination.