ORIGINAL ARTICLE

Abstract In this study we use a demographic approach to analyse the differing abundance of three congeneric columnar cacti: Neobuxbaumia macrocephala (the rar-est), Neobuxbaumia tetetzo (intermediate), and Neobux-baumia 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 spe-cies. Most matrices showed population growth rate (k) values close to unity; the only exception was N. mezcal-aensis in 2001–2002 (k=1.091±0.088). In the three species the highest elasticity values corresponded to en-tries referring to the stasis of pre-reproductive plant and small adults. However, the LTRE indicated that most important differences in the k values between years and species were associated with variation in fruit production and seedling recruitment. N. mezcalaensis yielded the highest mean k due to its high fecundity in 2001–2002. This result suggests that the variation in demographic behaviour observed between species is sufficient to explain the higher abundance of N. mezcalaensis com-pared to the rare N. macrocephala. The high fecundity values and recruitment success observed in the former, even if they occur only seldom, may result in higher average k values accounting for its high population densities