Isolda Luna-Vega

Species richness, endemism and conservation of Mexican gymnosperms

An analysis of the distribution patterns of 124 Mexican gymnosperm species was undertaken, in order to detect the Mexican areas with high species richness and endemism, and with this information to propose areas for conservation. Our study includes an analysis of species richness, endemism and distributional patterns of Mexican species of gymnosperms based on three different area units (states, biogeographic provinces and grid-cells of 1° × 1° latitude/longitude). The richest areas in species and endemism do not coincide; in this way, the Sierra Madre Oriental province, the state of Veracruz and a grid-cell located in the state of Oaxaca were the areas with the highest number of species, whereas the Golfo de México province, the state of Chiapas and a grid-cell located in this state were the richest areas in endemic species. A weighted endemism and corrected weighted endemism indices were calculated, and those grid-cells with high values in both indices and with high species richness were considered as hotspots; these grid-cells are mainly located in Southern and Central Mexico.

Conservation biogeography of red oaks (Quercus, section Lobatae) in Mexico and Central America

PREMISE OF THE STUDY Oaks are dominant trees and key species in many temperate and subtropical forests in the world. In this study, we analyzed patterns of distribution of red oaks (Quercus, section Lobatae) occurring in Mexico and Central America to determine areas of species richness and endemism to propose areas of conservation. METHODS Patterns of richness and endemism of 75 red oak species were analyzed using three different units. Two complementarity algorithms based on species richness and three algorithms based on species rarity were used to identify important areas for conservation. A simulated annealing analysis was performed to evaluate and formulate effective new reserves for red oaks that are useful for conserving the ecosystems associated with them after the systematic conservation planning approach. KEY RESULTS Two main centers of species richness were detected. The northern Sierra Madre Oriental and Serranías Meridionales of Jalisco had the highest values of endemism. Fourteen areas were considered as priorities for conservation of red oak species based on the 26 priority political entities, 11 floristic units and the priority grid-cells obtained in the complementarity analysis. In the present network of Natural Protected Areas in Mexico and Central America, only 41.3% (31 species) of the red oak species are protected. The simulated annealing analysis indicated that to protect all 75 species of red oaks, 12 current natural protected areas need to be expanded by 120000 ha of additional land, and 26 new natural protected areas with 512500 ha need to be created. CONCLUSIONS Red oaks are a useful model to identify areas for conservation based on species richness and endemism as a result of their wide geographic distribution and a high number of species. We evaluated and reformulated new reserves for red oaks that are also useful for the conservation of ecosystems associated with them.

Distribución de Taxus globosa (Taxaceae) en México: Modelos ecológicos de nicho, efectos del cambio del uso de suelo y conservación

Taxus globosa es una gimnosperma que habita principalmente en los bosques templados de Mexico y el norte de America Central, y que esta considerada como amenazada por las agencias de conservacion tanto mexicanas como internacionales. En Mexico, una de las mayores amenazas para la mayoria de las especies de los bosques nublados es la perdida de habitat, la cual se propicia por la modificacion de la cobertura vegetal por factores antropogenicos. Con base en 73 registros de herbario se obtuvo la distribucion potencial de la especie mediante el algoritmo Maxent. Asimismo, a partir del modelo obtenido se analizo la modificacion de la cobertura vegetal durante tres periodos (1976, 1996 y 2000) y su influencia en la distribucion potencial de esta especie. Su distribucion potencial fue evaluada en relacion con el actual Sistema Nacional de Areas Naturales Protegidas a nivel federal (ANPs) de Mexico y las Regiones Terrestres Prioritarias para la Conservacion (RTPs), con el fin de determinar el papel de estas areas en su conservacion y manejo. Los modelos de distribucion potencial muestran que existe una reduccion importante del area de distribucion (hasta el 84 %) al existir un cambio de uso de suelo. La especie esta mal representada en las ANPs, pues menos del 10 % de su area potencial se encuentra dentro de estas areas de proteccion federal. Este tipo de analisis representa una herramienta importante en biogeografia y conservacion, asi como en otras areas del quehacer biologico, debido a su habilidad predictiva. Nuestros resultados muestran la urgencia que existe de conservar algunos parches de bosques templados mexicanos (principalmente los bosques nublados) para garantizar la existencia de esta especie.

Species richness, endemism, and conservation of American tree ferns (Cyatheales)

Analyses of richness and endemism of Cyatheales (tree ferns) in tropical America were performed and evidence of a diversity gradient is presented. For this, the occurrence ranges of 239 species were plotted into a 5° × 5° grid-cell map and then analyzed using species richness and endemism indices. Here we show that species richness and endemism are not distributed randomly over the landscape, but do aggregate into defined regions of high diversity in tropical America: the northern Andes, lower Central America, upper Central America and Mexico, the Guyana Highlands, southeastern Brazil, and the Antilles. These distributional patterns are congruent with the geographical distribution of cloud forest, which in turn is determined by topography, high humidity, and persistent cloud immersion. The mountain regions of tropical America, especially the cloud forests, harbour most of the species of American Cyatheales and have high levels of habitat loss and climatic fragility. Conservation policies for Cyatheales are centred on the local use and trade of many tree fern species, but none such policies focus on cloud forest habitat loss. This makes tree ferns a critically endangered group of plants. In the face of the current environmental crisis and global climate change, the presence of Cyatheales in these regions sounds the alarm on their conservation priorities.

New Approaches to the Biogeography and Areas of Endemism of Red Oaks (Quercus L., Section Lobatae)

An area of endemism is defined by the spatial congruence among two or more species with distributions that are limited by barriers. In this study, we explored and discussed the use of the network analysis method (NAM) and neighbor-joining (NJ) to analyze the areas of endemism of Quercus sect. Lobatae (red oak species) in Mexico and Central America. We compared the NAM and NJ with other methods commonly used in biogeographic studies to show the advantages of these new approaches and to identify the shortcomings of other approaches. The NAM used in this study is based on notions of centrality measures, such as betweenness. We incorporated the strength of the ties within the internal networks through p-cores and aggregate constraints in iterative analyses. The NAM based on betweenness is ideal for recognizing completely allopatric areas of endemism. The iterative NAMs increase the number of possible areas of endemism because they minimize the effect of minimal overlap, and the p-core is efficient at identifying the closest relationships among species in the cases in which betweenness is not informative. The number of areas of endemism increases when the sympatry matrix minimizes the dispersal effect and the sample effort is maximized, allowing the identification of the greatest number of these areas. The NJ method supports the idea that areas diverge among themselves in a differential way; the long branches correspond to zones with high speciation rates and complex histories (biotic and tectonic), and the short branches correspond to zones with low speciation rates and simple histories. In a classification scheme, NJ was capable of identifying the areas that are considered biotically complex because of their high speciation rates. The results obtained with the NAM and NJ showed that the physiographic regions of Mexico are not natural units and that many of them are composed of at least two different biotic components.

Geographical patterns and determinants of species richness in Mexico across selected families of vascular plants: implications for conservation

Mexico is considered a megadiverse country containing more than 10% of the worlds biodiversity. The distribution of this species richness and endemism is different among the different Mexican states. We examined the species richness patterns of 13 families of vascular plants (including ferns, gymnosperms and angiosperms) in Mexico using political divisions (states) as units of analysis. We analysed the species richness values (absolute richness, endemic richness and restrictive richness) of these plant families using stepwise multiple regression analysis, assessing their relationship with a set of 10 environmental variables (expressed as heterogeneity coefficients). A combined cluster analysis with multidimensional scaling analysis (MDS) and an analysis of similarities were also undertaken to define the spatial–geographical patterns. Additionally, we proposed a methodological strategy to determine which states of Mexico have priorities for conservation. Our results suggested that the three species richness values used were significantly predicted by environmental factors, especially by climatic heterogeneity. Notwithstanding that a linear pattern was recognized, the Mexican states were gathered in four groups, which were confirmed by the MDS and the cluster analysis: (1) the Yucatan Peninsula, (2) arid Mexico, (3) the Mexican Transition Zone and (4) the megadiverse states. We proposed that 12 Mexican states include all the environmental conditions and are candidates for developing conservation programmes: (1) Quintana Roo, Tabasco and Yucatán, (2) Baja California, Chihuahua and Sinaloa, (3) Guerrero, Jalisco and Nuevo León and (4) Chiapas, Oaxaca and Veracruz.

Diversity, endemism and conservation of ferns (Polypodiales) in the Mexican Mountain Component

We analyzed the distributional patterns of 95 selected species of leptosporangiate ferns inhabiting the Mexican Mountain Component, using grid-cells of one geographical degree as unit areas, applying endemism indices and richness and beta diversity analyses. Distributional data were obtained from several herbaria and specialized literature. Five grid-cells appear to be important for fern species richness, as they contain 35 to 49 species. These grid-cells are located in the Sierra Madre Oriental (SMO), Trans-Mexican Volcanic Belt (TMVB) and the Sierra Madre del Sur (SMS). Mean richness by latitudinal belts of one degree showed that the belts with highest values are related to the TMVB and SMS. A total of 13 grid-cells were recognized as important from the perspective of endemism; most of them are located also in the SMO, TMVB and SMS. The richest gridcells coincided with one of the main centres of endemism for ferns obtained in this study, located in the convergence of the southern part of the SMO, the eastern portion of the TMVB and the northern part of the SMS, reflecting the high humidity existing on the mountain slopes facing the Gulf of Mexico. Some important grid-cells recognized from richness and endemism analyses coincide with Mexican Natural Protected Areas. The beta diversity analysis showed a low degree of similarity among grid-cells, implying a high species replacement, as the result of environmental heterogeneity occurring in the Mexican mountain systems. On the other hand, the spatial analysis suggested a pattern of phytogeographical regionalization comprising two main areas: the Mexican Transition Zone and the Mexican Central Plateau. Ferns play an important role in the Mexican biodiversity and contributing to the beta diversity of Mexico.

Geographic Differentiation of Tree Ferns (Cyatheales) in Tropical America

Abstract The patterns of geographic differentiation in fern species have been linked to climatic differences across regions and the distribution of available habitat. In this paper, the association between some climatic features and patterns of geographic differentiation in American tree ferns was evaluated. For this, the occurrence ranges of 190 species were plotted and then analysed using track analysis. Here we identify six generalised tracks that span the main highland regions of tropical America: the Andes, the Guyana Highlands, the Brazilian Atlantic coast, lower Central America, the Greater Antilles, and upper Central America-Mexico. We did not find an association between cloud forest habitat and the differentiation pattern revealed by generalised tracks in Central America. Instead, these patterns are congruent with well-documented geological boundaries in the region. Climatic variables associated with cloud forest habitat were extracted from each generalised track and subjected to ANOVA, showing that most tracks have equivalent climates. The Andean track showed significant climatic differences with the Brazilian and Guyanan tracks, which were associated with main habitat discontinuities. From these results, we propose that historical isolation has been important in promoting geographical differentiation in tree ferns and that differentiation by dispersal cannot fully explain the large-scale geographical patterns observed in tree ferns.

Current knowledge and importance of the order Gomphales (Fungi: Basidiomycota) in Mexico

Those species belonging to the order Gomphales (Fungi: Basidiomycota) are widely distributed, but most of them have been recorded in temperate areas of the northern hemisphere. This study presents the current knowledge and importance of this taxon in Mexico. Herbarium records, published works, institutional databases and personal collections in Mexico show that this order is represented in the country by 10 genera and 92 species, which chiefly inhabit temperate montane forests, although it is also represented at low altitudes. Traditionally, more than half of the species have a nutritional value among the different ethnic groups that inhabit Mexico. It is also known that many of the species are ectomycorrhizal. In comparison with other groups of Basidiomycota, there is little taxonomic knowledge about the species of this order, due chiefly to the lack of specialists on the group. Conservation of the members of this order is important for maintaining the delicate balance of temperate Mexican forests, mainly coniferous ones, which require association with fungi for their survival.

Contributions of Cladistic Biogeography to the Mexican Transition Zone

The Mexican Transition Zone (MTZ) was defined by Halffter (1987) as the complex area where Neotropical and Nearctic biotic elements overlap, including the southern United States, Mexico and adjacent areas of Central America. The biota of this area has received the attention of several naturalists since the mid 19th century (e.g. Sclater, 1858) due to its placement between the Nearctic and Neotropical regions and its “hybrid” character (Morrone, 2005 and references therein), associated with high biotic diversity and a high degree of endemism of plant and animal taxa. This area also has received attention in conservation and biodiversity plans at a worldwide level, because its central portion, the Mesoamerican hotspot, was considered one of the main biodiversity hotspots recognized in the world (Flores-Villela & Gerez, 1994; Luna-Vega and Contreras-Medina, 2010; Mittermeier et al., 1998; Myers et al., 2000).