Artículo de publicación ISIA high proportion of plant species is predicted to be threatened with extinction in the near future. However, the threat status of only a small number has been evaluated compared with key animal groups, rendering the magnitude and nature of the risks plants face unclear. Here we report the results of a global species assessment for the largest plant taxon evaluated to date under the International Union for Conservation of Nature (IUCN) Red List Categories and Criteria, the iconic Cactaceae (cacti). We show that cacti are among the most threatened taxonomic groups assessed to date, with 31% of the 1,478 evaluated species threatened, demonstrating the high anthropogenic pressures on biodiversity in arid lands. The distribution of threatened species and the predominant threatening processes and drivers are different to those described for other taxa. The most significant threat processes comprise land conversion to agriculture and aquaculture, collection as biological resources, and residential and commercial development. The dominant drivers of extinction risk are the unscrupulous collection of live plants and seeds for horticultural trade and private ornamental collections, smallholder livestock ranching and smallholder annual agriculture. Our findings demonstrate that global species assessments are readily achievable for major groups of plants with relatively moderate resources, and highlight different conservation priorities and actions to those derived from species assessments of key animal groupsConsejo Nacional de Ciencia y Tecnologia 000000000011820

Epiphytes are one of the most ubiquitous elements of tropical forest canopies, including seasonally dry tropical forests. Given the temporal variation in weather conditions in the latter, epiphyte populations may be subject to wide temporal variation in seedling recruitment, reproductive success, vegetative propagation and mortality rate. In this study, we use a 3-y demographic data set for Tillandsia brachycaulos to project its long-term population dynamics through the use of average and periodic matrices, as well as stochastic simulations. The results show that demographic behaviour varied over the 3 years of study, apparently in relation to rainfall. The first 2 years yielded a low λ value (0.79 and 0.80 – although only the former was significantly lower than unity), while the third year resulted in a λ = 1.08 (not significantly different from 1.0). When incorporating this demographic variation in an average matrix, a periodic matrix and stochastic simulations, the resulting overall λ was below unity in all three cases. The projections of the stochastic simulations suggest that the population would be able to persist in the long run only if the frequency of “good” years (defined here as those with an August rainfall above 200 mm) was above 0.6, which appears unlikely given that global warming might result in a lower frequency of rainy years in tropical dry forests.

Aim The purpose of this study was to examine the biogeographical relationships of the tree flora of the Yucatan Peninsula (YP2). To this aim we: (1) evaluated the affinities of political entities of tropical America with the Yucatan Peninsula, considering the distribution of tree species occurring in the latter region; (2) assessed floristic affinities between political entities of the Yucatan Peninsula based on endemic species; (3) defined biogeographical districts for the Mexican portion of the Yucatan Peninsula; and (4) evaluated the conservation status of endemic species in the area. Location The Yucatan Peninsula is a biogeographical area comprising the entire territory of the Mexican states Campeche, Quintana Roo, and Yucatan, adjacent small portions of Tabasco and Chiapas, the El Petén department in Guatemala, and the northern half of Belize. Because of heterogeneous data availability some analyses were restricted to the first three above listed Mexican states (YP1), which comprise the core of the Yucatan Peninsula. Methods Distributional data of 434 tree species were obtained from three sources: inspection of 7640 herbarium specimens, specialist advice regarding the taxonomic status of the tree species, and an extensive review of taxonomic and floristic literature. We based the various analyses of phytogeographical affinities on Jaccard's Index. Information on individual species distributions was subjected to a multivariate analysis. Occurrence of endemic species in five existing protected areas in the Yucatan Peninsula was analysed by examining floristic checklists available for them. Results Affinities of the tree flora of YP1 with twenty‐four political entities of tropical America generally decreased as geographical distances from this region increased. Distributional patterns of the seventy‐two tree species endemic to YP2 showed the strongest affinities to exist between Campeche, Quintana Roo and Yucatan, and in turn these entities displayed a large similarity with Belize and Guatemala. Regionalization of YP1, based on the distributions of both all species and the endemic ones, led to the distinction of two districts: a smaller one in the north‐western corner, and a larger one comprising the remaining areas. Although the distributions of numerous species in the two groups matched the limits of these districts, ubiquitous species of panpeninsular distribution also occurred. For YP1 we identified nineteen endemic trees, indicating a percent endemism of 4.4 for this area. Of the sixty‐four species endemic to YP2 which occur in YP1, fifty‐two (81.2%) have been recorded in at least one of the five protected areas of this territory (three occurred in the five preserves and nineteen did so in a single one), whereas twelve (18.8%) were not found in any protected area. Main conclusions The definition of the Yucatan Peninsula as a biogeographical province was confirmed. The strongest floristic affinities of YP1 were with Mesoamerican entities, whereas affinities with the Antilles were much weaker. The distincti...

We conducted a demographic examination of Pterocereus gaumeri, a rare and endemic columnar cactus of the Yucatan peninsula, Mexico. Growth, survival, and fecundity of individuals were recorded in two populations from 1997 to 1999. Size‐based population projection matrices were constructed to document the population dynamics. Seed germination and seedling establishment experiments were conducted in the field to estimate the rate of seed and seedling survival. Our results show that P. gaumeri did not reproduce by asexual means or vegetative growth and thus relies wholly on sexual reproduction for population growth. Low reproductive success, seed predation, and low seedling survival appear to be important factors that contribute to the rarity of this species. The population growth rate (X) varied between 0.9545 and 1.0316. According to the matrix elasticity values, population dynamics of this species depend mainly on adult survival, with low values in fecundity and survival for the lowest size categories. Our results did not indicate that the population size of P. gaumeri was decreasing; however, increasing pressure on land use transformation is one of the most important factors that may threaten the persistence of this species.RESUMENSe presenta un estudio demográfico de Pterocereus gaumeri, un cactus raro, y endémico columnar de la Peninsula de Yucatán, México. Desde 1997 a 1999, se registró el crecimiento, la sobrevivencia y la fecundidad de individuos en dos poblaciones. Se construyeron marrices de proyección basadas en tamano poblacional para documentar la dinámica de las poblaciones. Se realizaron experimentos de germinación de semillas y establecimiento de plántulas en condiciones naturales, para estimar la tasa de sobrevivencia de semillas y plántulas. Nuestros resultados sugieren que P. gaumeri no se reproduce asexualmente o por crecimiento vegetative, por lo tan to el crecimiento poblacional depende completamente de la reproducción sexual. El bajo éxito reproductivo, la depredación de semillas y la baja tasa de sobrevivencia parecen ser factores importantes que contribuyen a la rareza de esta especie. La tasa de crecimiento poblacional (λ) varia entre 0.9545 y 1.0316. De acuerdo con los valores de las matriz de elasticidad, la dinámica poblacional de esta especie depende principalmente de la sobrevivencia de los adultos, con valores bajos en fecundidad y sobrevivencia de las categorias de tamanos menores. Nuestros resultados no indican que el tamano poblacional de P. gaumeri esté decreciendo, sin embargo, el incremento de presion por el cambio de uso de la tierra es uno de los factores más significativos que puede amenazar la continuidad de esta especie.

Abstract. The distribution of plant taxa endemic to the Yucatán Peninsula was studied using Parsimony Analysis of Endemicity (PAE). The known distribution of 162 endemic plant taxa was plotted and the DOMAIN method together with environmental data were used to model the potential distribution for each taxon. The Peninsula was divided into a grid of quarter‐degree cells for the purpose of identifying distribution patterns. A total of 294 cells were analysed using known collection records and potential distribution of endemic taxa data. Two data matrices were constructed, a matrix of known distribution and a matrix of both the known and potential distribution. The two matrices were included in the PAE to identify areas of endemism. The areas determined with the known distribution were restricted and almost half of them remained unresolved, whereas with the potential distribution, approximately 90% of the cells were assigned to any one of the endemicity areas. Four endemism areas were identified: the Yucatán dry zone, Yucatán, El Petén and Belize. The areas of Yucatán and El Petén could be explained by current and Pleistocene climatic conditions and their congruence with other biological groups. Analysis of the potential distribution identified areas with patterns that share current environmental characteristics and a palaeoclimate history. Potential distribution modelling can eliminate uncertainties in biogeographical analysis caused by lack of data distribution and sample variation and produce information about the relationships between areas and taxa as well as the environmental affinities of taxa.