River Ecology and Restoration - River Dynamics and Integrated River Management - page 666

describe functional measurements of algal communities, such as primary productivity and community
respiration, to evaluate the effects of nutrient enrichment.
Although collecting algae in streams requires little effort, identifying for metrics, such as diversity
indices and species richness, may require considerable effort. A great deal of effort may be expended to
document diurnal and seasonal variations in productivity.

10.3.2 Metrics of Biodiversity

10.3.2.1 Richness and Abundance
If an indicator species group is selected, the ecosystem can be assessed by monitoring some variables of
the indicator species group, including the species richness, S ; the number density (or abundance), N ,
which is the total number of individuals per area; the biomass (the total weight of all individuals) per
area; and the number of individuals per area for each species. Many parameters representing biodiversity
of river ecosystems have been proposed. The species richness, S , is the most widely used index
(Magurran, 1988) and the most important characteristic of biodiversity:
S total number of species in the samples from a sampling site (10.2)
The ecological assessment and habitat conditions of streams may be mainly represented by the species
richness. In general, the samples should be identified to species level for all species. Nevertheless, it is
often not possible because to identity some species special instruments and experienced biologists are
needed. In this case these species may be identified to genus level or family level. This does not affect
the ecosystem assessment if the samples before and after the disturbance are examined by the same
biologist and to the same level. A simple measure of richness is most often used in conservation biology
studies because the many rare species that characterize most systems are generally of greater interest than
the common species that dominate in diversity indices and because accurate population density estimates
are often not available (Meffe et al., 1994).
In general there are more species within large areas than within small areas. The relation between
species richness, S, and habitat area, A, follows a power function formula (Ricklefs, 2001) :

(10.3)
where c and z are constants fitted to data. Analysis of species-area relations revealed that most values of z
fall within the range 0.20-0.35 for birds and fish, and within the range 0.05-0.2 for benthic macro-
invertebrates. For example, for the land-bird fauna of the West Indies, species richness increases from only
16 within an area of 10 km 2 to about 100 within an area of about 100,000 km 2 . The relation between S
and A is then (Ricklefs, 2001)

z
ScA

S (10.4)
The species richness increases with habitat area because habitat heterogeneity increases with the size
of the area (and resulting topographic heterogeneity) of islands in the west Indies, and larger islands
make better targets for potential immigrants from mainland sources of colonization. In addition, the
larger populations on larger islands probably persist longer, being endowed with greater genetic diversity,
broader distributions over area and habitat, and numbers large enough to prevent chance extinction.
The fish community, like birds, also occurs in a large area of habitat and the sampling area must be
large enough to a have reliable value of S . As a comparison, the macro-invertebrate community is more
localized and needs much less sampling area for assessment of local ecosystems. If a river ecosystem
with high heterogeneity of habitat is assessed with macro-invertebrates as indicator species, numerous
sampling sites should be selected to represent different habitat conditions. For each sampling site the
sampling area may be one or several m 2 . The work load increases with the sampling area, therefore,

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10 A