Columnar cacti-shrub relationships in an Andean semiarid valley in western Venezuela

Abstract

Spatial associations between columnar cacti and mimosoid shrubs were evaluated in an Andean semidesert enclave. An analysis on the capacity of other deciduous shrub species and medium-sized ephemeral plants to modify the spatial distribution of cacti was also included. The number of Stenocereus griseus (Haw.) F. Buxb., Cereus repandus (L.) Backeb. and Pilosocereus tillianus Gruber & Schaftzl that grow below the canopies of perennial plants were assessed and compared with open areas. Comparison of observed and expected number of cactus individuals shows a positive spatial association between S. griseus and Prosopis juliflora DC. Moreover, abundance of C. repandus and P. tillianus under the canopies of mimosoid shrubs were not statistically different from what was expected by chance. Positive spatial association between S. griseus and Capparis odoratissima Jacq., Cassia emarginata L., Cordia curassavica (Jacq.) Roem. & Schult., Croton rhamnifolius H.B.K. and Jatropha gossypifolia L. was also found. Evidence suggests that positive columnar cacti-shrub spatial association may occur either in the cactus thickets or in the thornscrubs. Due to the clumped distributions of S. griseus beneath P. juliflora and other perennial plants, we here postulate that S. griseus is the primary nursed columnar cactus of the enclave. The presence of cacti in open areas suggests that facilitation may be less important for establishment of columnar cacti species in this Andean semidesert landscape than in other temperate and tropical semiarid zones. We here discuss the importance of the nurse syndrome phenomenon for recruitment of S. griseus and for the conservation of this Andean semiarid environment.

Dinâmica espaço-temporal de Melocactus ernestii subsp. ernestii (Cactaceae) no Nordeste do Brasil

“…nurse plants ou plantas berçário (Flores & Jurado 2003, López & Valdivia 2007, Larrea-Alcázar & Soriano 2008. Embora associações entre cactos e plantas perenes tenham sido documentadas (Franco & Nobel 1989, Valiente-Banuet & Ezcurra 1991, Arriaga et al 1993, Reyes-Olivas et al 2002, Godínez-Álvarez & Valiente-Banuet 2004, Godínez-Álvarez et al 2005, Larrea-Alcázar & Soriano 2008, a importância destas associações na distribuição espacial de cactos globosos é pouco estudada (Mandujano et al 2002, Reyes-Olivas et al 2002, Larrea-Alcázar & Soriano 2008.…”

ESTRUCTURA ESPACIAL DE Pachycereus weberi (Coult.) Backeb. EN LA CAÑADA DEL ZOPILOTE, GUERRERO

“…Se puede observar que tanto los juveniles como los adultos presentan un patrón agregado en el terreno prácticamente en todas las distancias analizadas (0-25 m), aunque el grado de intensidad de agregación es ligeramente mayor en los juveniles (Figura 3). La mayoría de las especies de Cactaceae muestran una distribución espacial agregada, lo cual es un reflejo de la alta variación en la distribución de los recursos ambientales y del sitio a lo largo de su distribución (Valiente-Banuet y Ezcurra, 1991; Larrea-Alcázar y Soriano, 2008;ZentenoRuiz et al, 2009).…”

“…En la of a clumped pattern. It may be due to intrinsic or extrinsic factors; these two kinds of factors can also interact in many ways, affecting the evolutionary trajectory of the population or species at all levels of organization (Larrea-Alcázar and Soriano, 2008).…”

“…Cactus species have a well-documented relationship with bush and tree species that act as facilitators through the so-called nurse plant syndrome (Reyes-Olivas et al, 2002;López et al, 2007;Larrea-Alcázar et al, 2008;Larrea-Alcázar and Soriano, 2008;Zenteno-Ruiz et al, 2009). The fact that there is a positive spatial correlation at short distances (0-3 m) between P. weberi juveniles and Figura 4 se presenta la correlación espacial entre juveniles y adultos de P. weberi y Acacia tenuifolia.…”

“…En especies de cactáceas está ampliamente documentada la relación con especies arbustivas y arbóreas que funcionan como facilitadoras a través del síndrome de nodricismo (Reyes-Olivas et al, 2002;López et al, 2007;Larrea-Alcázar et al, 2008;Larrea-Alcázar y Soriano, 2008;Zenteno-Ruiz et al, 2009). El hecho de que se presente una correlación espacial positiva a distancias cortas (0-3 m) entre juveniles de P. weberi e individuos de Acacia tenuifolia, puede ser un indicio de la existencia de dicho síndrome.…”