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

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. In this study, we report an analysis of the population dynamics of the shrub Acacia bilimekii. We followed a population sample (N=314) for a one-year period (2001–02) and built a projection matrix. We also carried out germination and seedling establishment experiments in two contrasting conditions: a well preserved and an eroded site, and both under the shade of shrubs and in the open. The results of these experiments were used to calculate the fecundity entries for the transition matrix. Germination was not affected by microhabitat (shade vs. open conditions) or site (eroded vs. well-preserved). However, seedling establishment after 7 months was significantly higher under the shade than in exposed conditions. Finite population growth rate was significantly higher than unity (λ=1.23±0.173). Stasis was the demographic process that contributed mostly to λ (ca. 60%), followed by growth and fecundity. Even with a simulated decrease in fecundity values due to increased erosion, the A. bilimekii population would maintain a high λ-value. Thus, our results suggest that this population has the potential to persist even under relatively high disturbance levels.