PARENT SESSION
Poster Session # 7: Restoration, Resource Management, and Conservation.
Monday, August 4 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Distribution and abundance of three sympatric columnar cacti (Neobuxbaumia sp.) with different degrees of rarity.
Ruedas, Marcela1, Valverde, Teresa 1, 1 Lab. Especializado de Ecologia, Mexico, D.F., Mexico
ABSTRACT- The genus Neobuxbaumia includes nine species of columnar cacti endemic to the semi-arid regions of Mexico. In the Tehuacan-Cuicatlan region, well-known for its high floristic diversity regarding xerophytic vegetation, this genus is represented by three species which differ in their degree of rarity: Neobuxbaumia macrocephala (the rarest), N. tetetzo (intermediate), and N. mezcalaensis (the most common). We carried out a survey of 80 localities within the Tehuacan-Cuicatlan region in order to investigate the ecological factors that may be limiting their distribution and abundance, with the aim of understanding their differing degree of rarity. At each locality we recorded several biotic and abiotic variables, as well as the density of the Neobuxbaumia sp. population present. We subjected the data to a Principal Component Analysis (PCA) and a Canonical Correspondence Analysis (CCA) to identify the factors that account for the variation in the distribution and abundance of each of the three species. The results show that the factors that explain the distribution of the most common species (N. mezcalaensis and N. tetetzo) are mean annual temperature, altitude, rainfall, and soil properties such as texture and organic matter content. N. mezcalaensis reaches population densities of 5000-16000 plants/ha, coexists with Tecoma stans, Caesalpinia sp. and Aeschynomene sp., and is associated to localities with relatively abundant rainfall. N. tetetzo shows population densities of 8000-14000 plants/ha, coexists with Cercidium praecox, Leucaena sp. and Acacia cocliacantha, and is associated to high lalitudes and high phosphorous content in the soil. The rarest species N. macrocephala shows low densities (500-1200 plants/ha) and is associated to localities with high soil calcium content; it coexists with Calliandra sp. and Aeschynomene sp. Its distribution is limited to localities with specific values of the abiotic variables recorded, conferring it a high habitat specificity. This accounts for its higher degree of rarity.
Key words: Multivariate analysis, Rarity, Neobuxbaumia, Cacti