Fig. 1. Photosynthetically active incident radiation in an open space (diamonds) and under the crown of a Mimosa luisana shrub (squares). Data shown were recorded in a dry season, on April 18, 1999. In wet season, PAR differences between microenvironments are increased since shrub cover increase too.

Fig. 2. Mean (diamonds), maximum (squares) and minimum (triangles) soil temperature (5 cm deep) under the crown of a Mimosa luisana shrub (a) and in an open place (b). Data shown were recorded on April 18, 1999, but the differences between microenvironments were similar on all other days of measurement.

Fig. 3. Time to the onset of seedling emergence for species of three contrasting life-forms in the Tehuacán Desert under various experimental treatments (OE=open space with predator exclusion; O/E=open space without predator exclusion; SE=under shrubs with predator exclusion, and S/E=under shrubs without predator exclusion). Seeds of shrub species were scarified manually in order to simulate the natural conditions necessary for germination. The bar indicates ±1 standard error around the mean.

Fig. 4. Proportion of emerged seedlings for species of three contrasting life-forms in the Tehuacán Desert under various experimental treatments (OE=open space with predator exclusion; O/E=open space without predator exclusion; SE=under shrubs with predator exclusion, and S/E=under shrubs without predator exclusion). The bar indicates ±1 standard error around the mean.

Fig. 5. Survivorship curves for different species of three contrasting life-forms in the Tehuacán Desert under various experimental treatments (OE=open space with predator exclusion; O/E=open space without predator exclusion; SE=under shrubs with predator exclusion, and S/E=under shrubs without predator exclusion).

Fig. 6. Median survival time (st₅₀) for species of three contrasting life-forms in the Tehuacán Desert under various experimental treatments (OE=open space with predator exclusion; O/E=open space without predator exclusion; SE=under shrubs with predator exclusion, and S/E=under shrubs without predator exclusion). The bar indicates ±1 standard error around the mean.

Table 1. Monthly records of maximum and minimum air temperatures and total rainfall for the experimental period

Table 2. Analyses of variance from the onset of emergence of seedlings of different life-forms from Tehuacán Desert

Table 3. Analyses of variance from the final proportion of emerged seedlings of different life-forms from Tehuacán Desert

Table 4. Analyses of variance from the seedling survival of different life-forms from Tehuacán Desert