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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.
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