River Ecology and Restoration - River Dynamics and Integrated River Management - page 670

of habitat and made formerly diversified habitats very uniform and unitary. In general, the biodiversity
and bio-community indices are proportional to the diversity of habitats. The habitat loss and low
diversity of habitats result in low biodiversity and bio-community.
As indicated in the previous section biological diversity refers mainly to the number of species in an
area or region and includes a measure of the variety of species in a community that takes into account the
relative abundance of each species (Ricklefs, 1990). When measuring diversity, it is important to clearly
define the biological objectives, stating exactly what attributes of the system are of concern and why
(Schroeder and Keller, 1990). Different measures of diversity can be applied at various levels of complexity,
to different taxonomic groups, and at distinct spatial scales.
Overall diversity within any given level of complexity may be of less concern than diversity of a
particular subset of species or habitats. Measures of overall diversity include all of the elements of
concern and do not provide information about the occurrence of specific elements. For example, measures
of overall species diversity do not provide information about the presence of individual species, such as
Chinese sturgeon, or species groups of management concern. Thus, for a specific ecological restoration
project, measurement of diversity may be limited to a target group of special concern.

3. Alpha and Beta Diversities
Diversity can be measured within the bounds of a single community, across community boundaries, or in
large areas encompassing many communities. Diversity within a relatively homogeneous community is
known as alpha diversity, or local diversity. Usually the diversity indices obtained by examining the
samples taken from one site are referred to as alpha diversity. Diversity between communities in a
region, described as the amount of differentiation along habitat gradients, is termed beta diversity, or
regional diversity. For instance, the total number of species from numerous sites along a stream is the
regional diversity of the stream. Beta diversity may be large in river-lake connected habitats with high
heterogeneity, because some species colonize stream habitat and very different species may live in the
riparian lakes.
Noss and Harris (1986) note that management for alpha diversity may increase local species richness,
while the regional landscape (gamma diversity) may become more homogeneous and less diverse overall.
They recommend a goal of maintaining the regional species pool in an approximately natural relative
abundance pattern. The specific size of the area of concern should be defined when diversity objectives
are established.
A beta diversity index is given by the following formula:

M

E (10.11)

1

S

¦

m

i

S

i 1

in which M is the number of sampled habitats in a region, e.g., the middle reaches of the Yangtze River;
m i is the number of habitats, in which the i- th species is found; and S is the total number of species found
at all sampling sites in the region. If the species in all sites are the same, or m i M, the beta diversity
index is 1. If all species occur at only one site, m i 1 , the beta diversity index equals M . The total number
of species, S , in the region is then the product of the average species richness by the beta diversity index.
The ecological implication of beta diversity may be seen from the example of preliminary assessment
of aquatic ecology of the source region of the Yellow River. The benthic macro-invertebrates were
sampled at 8 sites with different environmental conditions in the source region of the Yellow River from
Aug. 7 to Aug. 15, 2009. Figure 10.42 shows the location of 8 sampling sites. Samples were taken from 5
sites from the Yellow River and riparian waters. In addition, samples were taken from a small stream on
the plateau, the Eling Lake and the Qinghai Lake. The sampling method is as follows: In mountain streams