Geoscience Reference
In-Depth Information
not presented). Similarly, subsets of data, such
as the EPT species, generally produce a weaker
signal (Marchant, 2007) or an inconsistent one
(Figure 14.2) but this seems to depend on the
diversity of higher taxa available. In the data used
here there are only 31 families of EPT species
compared with 81-91 families of insects in the
full dataset. Fewer families result in a narrower
taxonomic breadth, which in turn means a less
variable measure of delta
However, as an index of biological diversity its
insensitivity to sampling effort and its reflection
of changes in trophic diversity bode well for this
sort of use. Delta
+
may also be a valuable aid
to those using reference sites for bioassessment of
rivers (Bailey
et al
., 2004). The selection of suitable
reference sites is open to debate and is often based
solely on examination of routine environmental
(e.g. physical and chemical) conditions. Delta
+
provides a biological means of assessing whether
proposed reference sites have similar levels of
biodiversity, adding a perspective not usually
available.
+
.
Trophic diversity diminished continuously as
delta
declined with the current data, indicating
that this index of biodiversity was explicitly linked
to an aspect of functional diversity. Marchant
(2007) noted that for insect data from Victorian
river sites the delta
+
values for individual feeding
groups were always well below the expected
value. Thus, a decrease in delta
+
associated with
disturbance may be closely related to a change in
ecological conditions, e.g. the reduction in number
of species in one or more feeding groups. The
originators of delta
+
(Clarke and Warwick, 1998,
2001) acknowledged that they were surprised that
any conclusions about site diversity could be drawn
from a series of species lists collected with varying
sampling effort. The fact that delta
+
can be linked
to functional diversity reveals it has additional
characteristics that increase its robustness as an
indicator of disturbance.
+
Acknowledgements
We would like to thank Leon Metzeling of
EPA Victoria and Peter Goonan of EPA South
Australia for use of species level data held by their
organizations.
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Heino J, Soininen J, Lappalainen J, Virtanen R (2005)
The
Further use of delta
+
Average taxonomic distinctness is likely to be most
useful with large datasets collected over extensive
spatial scales, especially those where sampling
effort and technique have been variable. These
are the sorts of biological data that management
agencies may well possess but have not analysed
in detail because of the difficulties in compensating
for variable effort. To our knowledge, however, no
agencies have used delta
as a broad-scale measure
of disturbance. In Australia most agencies routinely
identify stream invertebrates only to the family
level, thus precluding its use.
Clearly, delta
+
needs to be tested against a
variety of stressors to determine whether it is
a generally sensitive measure of disturbance to
invertebrate communities over large spatial scales.
+
relationship
between species
richness
and
