Resumo

VALENCIA-DIAZ, Susana; FLORES-PALACIOS, Alejandro  e  CASTILLO-CAMPOS, Gonzalo. Population size and habitat characteristics of Mammillaria eriacantha, an endemic species of central Mexico. Bot. sci [online]. 2012, vol.90, n.2, pp.195-202. ISSN 2007-4476.

Habitat fragmentation reduces populations and can cause disappearance in species of restricted distribution. High degrees of endemism make many cacti species vulnerable to fragmentation Mammillaria eriacantha, a cactus endemic to central Veracruz, is restricted mainly to 22 isolated vegetation fragments each surrounded by cultivated land. The objective of this study was to estimate the population size of M. eriacantha and describe certain characteristics of the population and its habitat, considering fragmentation as a variable in the sampling design. Based on two-stage cluster sampling, six fragments of vegetation were randomly chosen. Within each fragment, ten plots of 5 × 5 m were randomly selected and the abundance of M. eriacantha within each plot was recorded, along with number of flowering adults, height of each individual and distance to the closest neighbouring M. eriacantha. In each plot, percentage of rockiness and coverage of grasses and canopy was recorded. Size structure of M. eriacantha was described, as well as its density, population size, number of adults, and spatial distribution pattern. Population variables were correlated with those of habitat. The estimated M. eriacantha population size for the total fragment area (9.53 km²) was 1,081,125.7 plants. Mammillaria eriacantha distribution was homogeneous, and no habitat variable was found to correlate with the measured M. eriacantha population characteristics. Notwithstanding the considerable size of the M. eriacantha population, the ongoing transformation of its habitat by exploitation and modification for agriculture could modify its population structure and abundance, so the establishment of sound management and conservation of this species is an important issue.

Palavras-chave : fragmentation; Mexico; population size; population structure; tropical dry forest; Veracruz.

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