Biología

Abstract. Pattern analysis and association analysis showed that recruitment of the giant columnar cactus Neobuxbaumia tetetzo in the semi-arid valley of Zapotitlán is largely limited to areas beneath the canopies of perennial shrubs, acting as nurse plants. Chi-square and Haberman tests revealed that young cacti were more frequently found beneath canopies of leguminous shrubs, especially Mimosa luisana, than were older cacti. Segregation analysis indicated a positive association (= negative segregation) of young cacti and M. luisana canopies, but older cacti were randomly distributed with respect to M. luisana. This, and the height class distributions of cacti associated withM luisana or not, suggested the replacement of M. luisana by N. tetetzo. Mimosa luisana plants in association withiV. tetetzo had greater amounts of dead basal area thanM luisana lacking associated N tetetzo. This suggested competition from JV. tetetzo promotes the replacement process.The roots of N tetetzo are ≤ 30 cm deep. Interception of soil water before penetration to deeper roots of M luisana may be the mode of competition between the two species.

... may be described as an extremely rare species (Rabinowitz, 1981) because it exhibits narrow geographic range (Meyrán, 1973; Bravo-Hollis, 1991; Bravo-Hollis and Sánchez ... Part of this area is now a Biosphere Reserve (Zavala-Hurtado and Hernández-Cárdenas, 1998). ...

Loss of shoot-tip because of severe, but non-lethal, injury is a common event in the life-cycle of giant columnar cacti. Repair (reiteration) could adversely affect further growth and reproduction because of a reassignment of resources. We studied a population ofCephalocereus hoppenstedtiiin Central Mexico, comparing growth rates, age of first reproduction and number of flowers produced per individual in repaired and

Resumo: Taking the view that morphological characteristics represent behavioral strategies of plants to cope with environmental pressures, we defined 18 life-forms, using multivariate classification techniques in a tropical semiarid ecosystem in Central Mexico. A multiple ...