Ecological genetics of resource specialization in Polysphondylium pallidum

The cellular slime molds (CSMs) are amebal predators of forest soil bacteria; it has been hypothesized that abundances of CSM species are determined by specialization on different bacterial prey and by the availability of these resources in the soil (Horn 1971). Previous studies have not taken intraspecific variation into account when characterizing species.; Genet diversity in natural populations of Polysphondylium pallidum was assessed using a resource consumption rate (RCR) assay under common garden conditions. Genet diversity was present in soil samples as small as a single soil core 1.1 cm in diameter x 1 cm deep; diversity was abundant in all samples collected from 1 m{dollar}sp2{dollar} plots. Change in P. pallidum diversity was recorded in one m{dollar}sp2{dollar} plot over a 20 month period. Differences among spatially separated sample plots were found also. Populations in two m{dollar}sp2{dollar} plots separated by 50 m were differentiable; differences among samples from woodlands up to 10 km apart were no greater than those between plots within a woodland. Bacterial type used in RCR assays had a strong impact on the distributions obtained.; Evidence for resource specialization equivalent to the evidence for species level specialization was obtained at the genet level; relative RCR of isolates reversed on different prey. Comparison of four CSM species revealed interspecific differences in excess of variation within species.; Resource specialization at both intra- and interspecific levels was tested in the field by manipulation of the diversity of bacterial resources. Three types of bacteria were added to field plots once a week for twelve weeks. No evolutionary responses within P. pallidum were found; no significant community level changes occurred either. The CSM guild did not appear to be resource limited during the time of the experiment.