PARENT SESSION
Oral Session # 1: Ecological Theory I: Theory; Scaling.
Presiding: M Pascual
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 100.
Development of environ indirect effects in ecological flow networks: Initial lessons from the Neuse River Estuary.
Borrett, Stuart*,1, 1 Institute of Ecology, Athens, GA
ABSTRACT- Indirect interactions are a critical component of ecological environments and are one source of biocomplexity. Results from environ analysis suggest that indirect flow intensities tend to dominate direct flow intensities in conservative transaction networks. One criticism of network environ analysis, however, is that it sums interactions over pathways of infinite length, thus implicitly assuming infinite time. In this paper, I investigate the development of environ indirect effects to determine the validity of this assumption and the robustness of the conclusion that indirect flow intensities tend to dominate direct in ecological networks. The analysis presented is restricted to the output oriented throughflow case of environ analysis. I used two threshold values to measure development of indirect flow intensities in the extended pathway network. The first, kI>D, is the pathway length at which indirect flow intensities surpass direct. The second, k95, is the pathway length at which 95% of the integral (direct + indirect) throughflow is achieved. These thresholds were measured in a seven compartment nitrogen cycling model developed for the Neuse River Estuary, and parameterized for sixteen seasons from 1985-1989 (Christian, R.R., Thomas, C.R. 2000. Neuse River Estuary Modeling and Monitoring Project Stage 1: Network Analysis for Evaluating the Consequences of Nitrogen Loading. Water Resources Research Institute of the University of North Carolina, Report 325-F). In all sixteen networks kI>D=3, and the mean k95 was 224 (±149 SD). Variation in k95 correlates with both total system throughflow (R2 = 0.72) and the degree of cycling (Finn cycling index, R2 = 0.92). These results indicate that very short durations of system stasis may be sufficient for indirect flow intensities to dominate direct, but that longer durations are required for full development.
Key words: environ analysis, indirect effects, network analysis, biocomplexity