Zoological Studies

Vol. 36 No. 3, 1997

A New Method to Establish Scoring Criteria of the Index of Biotic Integrity

Shih-Hsiung Liang1,* and Bruce W. Menzel2

1Department of Zoology, National Taiwan University, Taipei, Taiwan 106, R.O.C Tel: 886-2-3630231 ext. 2121. Fax: 886-2-3631694
2Department of Animal Ecology, Iowa State University, Ames, IA 50011, USA

Shih-Hsiung Liang and  Bruce  W. Menzel  (1997)  A  new  method  to  establish  scoring criteria of  the Index  of Biotic Integrity. Zoological Studies 36(3): 240-250. Karr's Index of Biotic Integrity (IBI) was applied in north central Iowa streams to examine the technique's utility for measuring environmental quality in agriculturally­ influenced streams and to develop  methodological improvement. During 1988 and 1989,  fish  were collected in the Boone River and Lizard Creek systems, and physical and chemical measurements of stream environ­ mental conditions were taken. A modified two-step procedure was proposed for establishing the scoring standard of the 12 IBI metrics. First, a simple linear regression relationship of the metric variable on  log drainage area was calculated(p = 0.1). If a significant correlation was  found,  a Maximum-Species-Richness Line (MSRL) was determined by calculating the 95% Y-intercept as its intercept, and then plotted  by  the original regression slope. If a nonsignificant relationship was obtained, the upper and lower  5% data points were deleted to define the upper  and lower boundaries  of the remaining  points with  horizontal  lines.  Final­  ly, the area below the calculated 95% MSRL and the area between the two horizontal lines were equally trisected into above average (5 point), average (3 point), and below average (1 point) categories. After the scoring criteria were established, the IBI value of each sampling site in Boone  River  and  Lizard  Creek systems was calculated.
The new scoring procedure resolved the problem of the commonly adopted "eye-fit" method through generating only a single MSRL for a given data set.  In Lizard Creek, IBI results  were  generally  consistent with evaluations of  physical  and chemical  environmental  quality.  During  the drought  period,  variations  of IBI scores reflected the dynamics of environmental conditions in the sampling sites. Additionally,  the IBI showed greater temporal consistency than another commonly used analytical tool, the Shannon-Weiner Diversity Index. Thus, the new  scoring procedure  seems  to  advance  the effectiveness  of  IBI in assessing the environment quality of lotic waters. Numerical species metrics  associated  with  species diversity  were more important than proportional ones in contributing to the IBI. Drought conditions throughout  the  study period influenced some of the data and analytical results.

Key words: Biological indicator, Index of Biotic Integrity, Environmental assessment, Stream fishes, Com­munity ecology.

*Correspondence: Department of Zoology, National Taiwan University, Taipei, Taiwan 106, R.O.C Tel: 886-2-3630231 ext. 2121. Fax: 886-2-3631694.