The distribution of macroinvertebrate communities is influenced by a myriad of abiotic
environmental factors. However, many of these environmental factors do not occur
randomly within a river system. Rather, they occur as a result of geomorphological
processes that operate hierarchically to constrain the expression of environmental
factors at successively nested levels. As a result of the hierarchical expression of
geomorphological processes, environmental factors occur at characteristic scales within
a river system and can be used to define spatial scales of river system organisation.
Previous studies have examined multiscale patterns of benthic macroinvertebrate
community distribution using scales of measurement such as ecoregions, catchments,
rivers, reaches and functional habitats. However, none of these studies used scales
derived from a geomorphological hierarchy to examine patterns of macroinvertebrate
distribution. Given that macroinvertebrates are often deterministically influenced by
environmental factors, and these environmental factors occur at characteristic scales
within a geomorphological hierarchy, it is possible that the multiscale distribution of
macroinvertebrate communities may correspond to the hierarchical arrangement of a
river system. This study used scales of measurement derived from a geomorphological
hierarchy to examine whether there was any congruence between the distribution of
macroinvertebrate communities and the organisation of a river system at the catchment,
zone, reach and riffle scales.
The Upper Murrumbidgee River Catchment study area (13 005km/2) was divided into
catchments, zones within catchments, reaches within zones and riffles within reaches.
Macroinvertebrate collection was stratified across these scales according to a balanced
nested hierarchical design, and environmental data were also collected at the catchment,
zone, reach and riffle scales. Simultaneous multiscale treatment of biological and
environmental data allowed identification of multiscale patterns of macroinvertebrate
distribution in relation to the hierarchical organisation of a river system, as well as
identification of hierarchical interactions between macroinvertebrate communities and
environmental factors. Multivariate (ANOSIM, classification, ordination) and
univariate (Nested ANOVA) statistical techniques were employed, and each analysis
was performed at the species and family levels of taxonomy.
Macroinvertebrate communities were highly similar within a reach, because this is the
point in the geomorphological hierarchy where environmental conditions become more
homogeneous, relative to larger scales. Conversely, communities were dissimilar at the
larger zone and catchment scales because environmental conditions become more
heterogeneous, relative to smaller scales. However, the reach within zone scale also
represents the point where sampling reaches become distinct across the landscape, and
the similarity of macroinvertebrate communities within a reach may also be related to
the spatial proximity of samples. Hence, macroinvertebrate community distribution is
only congruent with the smaller scales of river system organisation.
Despite the lack of congruence between macroinvertebrate community distribution and
the larger catchment and zone scales of river system organisation, there was a strong
regional pattern of distribution in the Upper Murrumbidgee River Catchment. This
regional-scale pattern self-emerges from biological information, and is larger than the
geomorphologically derived catchment scale. Partitioning of macroinvertebrate data
into regional groups subsequently revealed some congruence between
macroinvertebrate distribution and the catchment and zone scales of river system
organisation. An alternative hierarchy consisting of biological regions, biological
clusters, geomorphological reaches and geomorphological riffles was marginally better
able to capture patterns of macroinvertebrate distribution than the original catchment,
zone, reach and riffle scales. Thus, consideration of the hierarchical organisation of
stream systems from a purely physical perspective may fail to encompass scales that are
relevant to biota, and biological information should be included as a primary
hierarchical component of landscape-scale studies of macroinvertebrate distribution.
The pattern of region and reach-scale macroinvertebrate distribution was matched by a
general pattern of large catchment and local reach-scale environmental influence. This
occurred despite testing of catchment, zone, reach and riffle-scale environmental
variables against both the scaled and non-scale pattern of macroinvertebrate
distribution. Macroinvertebrate communities were influenced by local reach-scale
characteristics such as riparian vegetation character and channel morphology, but rifflescale
hydrological variables were also associated with some headwater communities.
However, macroinvertebrate communities also sit within a broader landscape context
and are influenced by large catchment-scale factors such as landuse, or by factors
indicating the geographical position of the sample or the size of the stream. The large
and local-scale environmental variables that influence macroinvertebrates are related
within a geomorphological hierarchy, and macroinvertebrates may respond
deterministically to the same type of environmental factor expressed at different scales.
These responses should not be treated as statistical correlates, but rather, they should be
viewed in the context of a hierarchy of river system organisation.
There was little difference in the overall scale-related findings between species and
family level. Family-level macroinvertebrate communities were similar within a reach
and dissimilar among reaches, zones and catchments and there was a large regionalscale
pattern of family-level community distribution. Local reach-scale and large
catchment-scale environmental factors were most strongly associated with family-level
macroinvertebrate distribution. Replication of these scale-related findings at both levels
of taxonomy indicates that aggregation from species to family level does not result in
loss of ecological information pertaining to primary hierarchical patterns. However, the
difference between species and family level was pronounced when tracing the
hierarchical occurrence of individual taxa, in the context of theories such as the
landscape filters hypothesis and habitat based model. In particular, there was a shift in
the scale at which families began to be removed from the hierarchy from the region to
the smaller cluster scale. This shift was related to the lowered distinctiveness of familylevel
regional macroinvertebrate groups, but also suggests that environmental filters
may act differently on species and families. The use of family-level data is not
recommended for the testing of theories of hierarchical taxon occurrence, because these
theories rely on the accurate detection of precise macroinvertebrate-environment
relationships.
The use of scales of measurement derived from a geomorphological hierarchy provides
a process-based foundation for marrying the biological and physical domains, and for
examining the hierarchical interactions that may occur between these domains.
However, the results of this study indicate that overlaying the biological and physical
domains is not a straightforward task, because the biological domain may be influenced
by factors other than the deterministic relationship between macroinvertebrates and
environmental conditions. Regardless, this study has taken some basic principles of
fluvial geomorphology and incorporated them into the design of a standard stream
ecology study. Given the relatively advanced state of knowledge that exists
individually in the disciplines of fluvial geomorphology and stream ecology, integration
and application of concepts across disciplines represents an exciting future opportunity
in aquatic science.
| Identifer | oai:union.ndltd.org:ADTP/219599 |
| Date | January 2001 |
| Creators | Parsons, Melissa, n/a |
| Publisher | University of Canberra. Science & Design |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Melissa Parsons |
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