Jeffrey R. Duncan’s research while affiliated with University of Tennessee at Knoxville and other places

Experimental testing of ecological theory in the field is often difficult because of the number of factors influencing the test system. Adequate control of relevant variables may require the use of laboratory microcosms for the performance of proper experimental tests. Our efforts to study the effects of species invasion sequence on community structure and ecosystem properties of the developing system, requires that the experimental systems be closed. To meet our demanding experimental requirements, we have designed a closed artificial stream that permits careful control over algal species introductions while minimizing the risks of contamination by unwanted species. In assessing the performance of these streams, we examined the variability among experimental replicates in water chemistry parameters and biomass accumulation. Those water chemistry parameters that were not greatly influenced by biological processes in the streams (Ca, Mg, bicarbonate, and sulfate) had average coefficients of variation less than 10%. Those parameters that were clearly influenced by biological processes (P, N, Fe, and Si) had average coefficients of variation ranging from 13.5%–40.4%. Ash free dry mass had an average coefficient of variation of 23.3%, but chlorophyll a was much more variable at 183%. This pattern of variation indicates that the artificial streams performed well in terms of replicability, but some experimental goals may require carefully conceived designs that adequately partition sources of variation in biologically mediated variables to obtain satisfactory results.

1. An ecological landscape consisting of discrete interconnected patches was constructed in the laboratory. Each patch in the landscape was a 1-litre aquatic microecosystem containing producers and consumers. 2. Species invaded and spread throughout the landscape in a specific sequence following prescribed invasion pathways. 3. Species distribution among landscape patches was heterogeneous and converged to one of several alternative states despite identical initial conditions. 4. Differences in structure which developed among patches were the result of the assembly processes which occurred in each patch and among interconnected patches. Variance in species composition increased as a function of distance from the patches that served as entry points for invasions into the landscape. 5. The development of organization at the landscape level results from the interplay between the assembly of individual patches and the constraints imposed on each patch by invasion among patches. 6. Differences in invasion success and persistence led to the development of alternative community states.