Environmental Engineering Reference
In-Depth Information
Combined index of biodiversity
complex situation - molecular studies and micro-
scopic analysis.
Clearly, species richness and evenness (or domi-
nance) both contribute towards mixed population
diversity, and a most useful approach would be to
bring these together as a single value. The Shannon-
Wienerdiversityindexisthemostcommoncombined
measure of diversity, taking into account richness,
evenness and abundance of the community structure
and assumes that individuals are randomly sampled
from an infinitely large population (Mason, 2002).
The Shannon-Wiener index may be expressed as
2.6.1 Molecular analysis
Molecular analysis of environmental algal popula-
tions involves techniques such as oligopeptide anal-
ysis, gene sequencing and use of molecular probes.
Oligopeptide analysis
H
′
=
∑
P
i
(1og
n
P
i
)
Different algal strains within a particular species pop-
ulation can be analysed in relation to the diversity and
pattern of their oligopeptides. In the case of the colo-
nial blue-green alga
Microcystis
, for example, Welker
etal
. (2007) have demonstrated the occurrence of dis-
tinct oligopeptide groupings or chemotypes.
These
Microcystis
chemotypes reflect variants
of particular gene clusters and are major fac-
tors influencing the toxin (microcystin) content of
blooms. They can be considered as evolutionary
units (withinteraction and competition within species
between phenotypes) and show significant differ-
ences between planktonic and sediment popula-
tions. Chemotypes undergo seasonal changes which
reflect their ecophysiological characteristics. Individ-
ual
Microcystis
strains differ considerably in their
functional responses to nutrient and light availability,
particular growth factors and susceptibility to grazing
by herbivores.
(2.13)
where
H
′
is diversity and
P
i
=
n
i
/
N
, with
n
i
and
N
as
in Equation (2.12).
In practice, plankton diversity is typically linked
to productivity, as indicated by total algal biomass. A
recent study by Skacelova and Leps (2014) on stand-
ing waters in the Czech Republic, for example, has
shown that diversity was normally low in conditions
oflowandhighproductivity-wherealgalgrowthwas
respectively restricted by low nutrients and competi-
tion for light. Maximum algal diversity was found in
situations of intermediate productivity, but even here
there were examples of low diversity indices - indi-
cating that low phytoplankton diversity can be caused
by a wide range of factors. Further aspects of algal
diversity in lakes are discussed in Section 3.2.3.
2.6 Biodiversity within single-species
populations
Gene sequencing
The recent introduction of comparative sequence
analysis of ribosomal RNA genes (phylogenetic
marker genes) has indicated high molecular vari-
ation within individual species based on morpho-
logical criteria (morphotypes). Recent studies by
Pfandl
et al
. (2009) on small subunit ribosomal RNA
(SSU rRNA) sequences in samples of the chrys-
ophyte
Spumella
, have demonstrated considerable
local heterogeneity - with individual populations
composed of different ecotypes and genotypes. Sim-
ilarly, genetic analysis of the chlorophyte
Desmod-
esmus
by Vanormelingen
etal
. (2009) has also shown
Although classical limnology has concentrated par-
ticularly on the species composition of phytoplank-
ton assemblages, new analytical techniques can also
provide information on variation within species and
the environmental presence of intra-specific sub-
populations. Studies on diversity at the subspecies
level are complicated by the fact that natural phy-
toplankton populations are typically a complex mix-
ture of different species - so bulk analysis procedures
cannot be used. Two major approaches have the res-
olution to study intra-specific variation within this
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