PARENT SESSION
Poster Session # 21: Biogeography, Biodiversity, Populations, and Genetics.

Thursday, August 7 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Population dynamics of the shrub Acacia bilimekii in a semi-desert region in Central Mexico.

Jiménez-Lobato, Vania¹, Valverde, Teresa¹, ¹ Lab. Especializado de Ecología, Mexico, D.F., Mexico

ABSTRACT- Shrubs are important elements of semi-desert vegetation. They provide microhabitats for the establishment of many species under their canopies thus maintaining community structure and diversity. Yet, little is known regarding their population processes and the factors that affect them. Recent soil erosion resulting from habitat degradation related to human activities may potentially affect the regeneration of shrub populations, thus altering the dynamics of complete semi-desert communities. We studied the population dynamics of the shrub Acacia bilimekii in the Tehuacan Valley through the analysis of population projection matrices (2001-2002). Additionally, we carried out germination and seedling establishment experiments in two sites: a well preserved and a relatively eroded one; in each site, experiments were performed both under the shade of shrubs and in the open. The results of these experiments were used to calculate the fecundity entries for transition matrices and project population dynamics in different theoretical scenarios (i.e. different disturbance degrees, and presence/absence of clonal propagation). Germination was higher in the eroded than in the well preserved site, and germination percentages were similar under the shade and in the open. However, seedling establishment followed the opposite trend, with highest values in the well preserved site and under the shade of shrubs. Population growth rate was significantly higher than unity in all cases. Stasis was the demographic process that contributed mostly to (c.a. 60%), followed by growth and fecundity. According to the germination and establishment result, the population would grow slightly faster (=1.23) in the well preserved site compared to the eroded site (=1.20). The scenario that incorporated clonal propagation projected a population with a slightly higher growth rate (1.29 and 1.26 respectively). These results suggest that A. bilimekii populations have the potential to persist, withstanding relatively high levels of disturbance conferring semi-desert communities a certain degree of ecological resistance.

Key words: Acacia bilimekii, demography, semi-desert shrubs, matrix models