This study was an investigation of lotic macroinvertebrate distribution in
northeastern Oregon at two different spatial and biological scales. Examination
of assemblages at a limited spatial scale revealed relationships with natural and
disturbance gradients and led to questions about distribution of a population at
broader spatial scales.
In a 16 kilometer section of the North Fork John Day River, I examined
the relationship of invertebrate assemblages to habitat and fine sediment
deposition. This river section was subjected to sediment inputs resulting from
several years of floodplain mine-tailing leveling, and erosion and tributary
channel scouring following a forest fire. Invertebrate assemblages differed
between habitat types. The proportion of sediment tolerant invertebrates,
especially oligochaete worms, increased with higher amounts of deposited fine
sediment, but total invertebrate abundance was not related to deposited
sediment. The response of sediment tolerant invertebrates appeared to reflect
cumulative impacts from multiple input points and downstream transport of
sediment and cumulative and/or increasing impacts over the two years of
sampling.
In studying assemblages in the North Fork, I noticed an unusual
abundance of the caddisfly, Lopidostoma pluviale (Milne). In a more spatially
extensive examination of a population, I investigated distribution of this
caddisfly in the Blue Mountain region of northeastern Oregon. L. pluviale was
more common and/or abundant further downstream than would be expected for
a shredding feeder based on the River Continuum Concept (Vannote, et al.,
1980). Through gut content analyses, I demonstrated that this species is much
more of a generalist feeder than its designation as a shredder would imply.
Consequently, its distribution is not limited to headwaters where allochthonous
food resources are abundant. I hypothesize that non-food environmental factors
may be more important in determining the distribution of this species.
Results of this research indicate that assemblage studies can reveal
interesting relationships with environmental conditions. In addition, paying
attention to unusual distributions of taxa in assemblage studies can lead to
further studies that can improve our understanding of the biology and ecology of
species. / Graduation date: 2004
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/30420 |
| Date | 12 March 2004 |
| Creators | Gerth, William J. |
| Contributors | Li, Judith L. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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