The bacteria are the first to multiply in great numbers, as evidenced by microscopic examination and the increasing turbidity of the medium. Although spores of other organisms are present, they will not develop as rapidly.
Bacterial decomposition converts the organic materials in the medium into food which will support the growth of a variety of protozoa.
Each different form of protozoa will make its appearance in stages, as environmental conditions become favorable.
The disappearance of the various organisms and appearance of others points out that as the food supply of each kind of organism becomes progressively depleted, their numbers decrease. Reductions in the bacterial population, accumulation of organic wastes, and changes in the pH of the water are some of the factors which can cause the decline of protozoan populations.
If the culture is kept in a lighted area, in time, green algae will appear and if maintained in light, will multiply rapidly. The autotrophic algae provide a continuous food supply for the animal population, thus stabilizing the community.
As the culture ages, protozoans will be present, but in very small numbers. Often, the appearance of rotifers indicates the rapid decline of the protozoan forms. If crustacean eggs, such as those of the freshwater shrimp, were present in the soil, then the larvae and adult forms of these will be present at the end of 3 weeks.
Your findings from the rehydrated desert soil will vary with the type of culture started. However, it can be expected that bacteria will appear first, then flagellates (e.g., euglena). As the flagellates decline in numbers, ciliates multiply.
The climax community contains a few bacteria and protozoa, algae, rotifers, and some crustacean forms.
Some generalizations you should try to make while doing the activity include: