The Relationship Between Cellular Slime Molds and Bacteria in Forest Soil

Abstract

Observations of natural and manipulated populations were used to investigate the regulation of population sizes and community structure in a group of soil amoebae, the cellular slime molds (Dictyosteliida). Correlations of slime mold abundance and distributional patterns with soil bacteria in the field suggest that food supply is a potential factor in the regulation of these species' numbers. One species, Dictyostelium mucoroides, responds most visibly to seasonal changes, spring and fall being peak seasons. When total slime mold number are partitioned into active and encysted forms, amoebae account for as much as 51% and 24% of the population in the fall and spring, respectively, vs. only 10—12% of the population during the summer and winter months. Large additions of various bacteria to field plots caused significant increases in D. mucoroides numbers. Moreover, the ability of this species to respond to a second addition of bacteria, made several days later, depended on its density. High—density populations failed to respond to additional food, whereas those which had already returned to base levels showed increases. These findings support the hypotheses that cellular slime molds are food limited in nature, and that community diversity is due, at least in part, to differential resource utilization by the species in nature.