SPATIAL HETEROGENEITY IN 8 CENTRAL TEXAS GRASSLANDS

1 Spatial heterogeneity in the environment has important consequences for the population biology of plants. In order to test hypotheses abou t how spatial heterogeneity affects natural plant populations, we need to be able to compare the amount and pattern of environmental spatial heterogeneity between sites. 2 Spatial heterogeneity between and with in eight grassland sites was documented using the performance of Boute loua rigidiseta (a perennial bunchgrass) transplants as indicators of microsite quality. Spatial heterogeneity was found to be consistently greater within sites than between sites. 3 Two components of within-si te spatial heterogeneity were recognized: (1) overall variation and (2 ) the degree of spatial autocorrelation. These components were not cor related with each other, suggesting they provide independent measures of spatial heterogeneity. Spatial autocorrelation was detected within most sites, however, mosaics may be the more common pattern of spatial heterogeneity, as indicated by the many more instances where spatial autocorrelation was not detected. 4 Spatial heterogeneity was characte rized using four different plant characters. The results were characte r-specific, which agrees with studies of phenotypic plasticity where e nvironmentally induced responses are specific to particular characters and specific to the environmental factor being considered. 5 In gener al, spatial heterogeneity was not related to transplant performance or characteristics of the vegetation. However, within-site variation in plant size was negatively correlated with survival, indicating that wi thin-site variation may be, in part, a measure of the number of favour able microsites within a site.