comparative demographic analysis of three neobuxbaumia species (cactaceae) with differing degree of rarity

In this study we use a demographic approach to analyse the differing abundance of three congeneric columnar cacti: Neobuxbaumia macrocephala ( the rarest), Neobuxbaumia tetetzo ( intermediate), and Neobuxbaumia mezcalaensis ( the most common). Populations of these species were studied in the Tehuacan Valley ( Central Mexico) over a 3-year period. We employed traditional models and life table response experiments (LTRE) to explore the association between particular demographic traits and the degree of rarity of each species. Most matrices showed population growth rate (lambda) values close to unit

demographic analysis of a rare columnar cactus (neobuxbaumia macrocephala) in the tehuacan valley, mexico

In this study we used population projection matrices to evaluate the conservation status of Neobuxbaumia macrocephala, a columnar cactus endemic to a small region in the Tehuacan Valley, in central Mexico. Demographic data included 2-year observations on growth, fecundity and survival of individuals classified by size. Our results indicate that the population is comprised of 70% juveniles. Population growth rate was 0.979 and 0.994 for the 1997/1998 and the 1998/1999 periods, respectively. The slight increase in A in 1998/1999 was a result of increased fecundity and seedling survival. The highest elasticity values correspond to the survival of large/old individuals. Numerical simulations were performed by changing the value of particular matrix entries and directly evaluating their effect on lambda. Population growth rate reached values above unity only when either fecundity or seedling survival probability were increased 10-fold. Given these limitations for population growth, along with its limited distribution range and low population densities, we propose N. macrocephala to be classified as a rare species and to promote its conservation by favoring management practices aimed to increase germination and seedling establishment success. (C) 2001 Elsevier Science Ltd. All rights reserved