Graduate Thesis Or Dissertation
 

Distribution of nearshore macroinvertebrates in lakes of the northern Cascade Mountains, Washington, USA

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  • Although nearshore macroinvertebrates are integral members of high mountain lentic systems, knowledge of ecological factors influencing their distributions is limited. Factors affecting distributions of nearshore macroinvertebrates were investigated, including microhabitat use and vertebrate predation, in the oligotrophic lakes of North Cascades National Park Service Complex, Washington, USA, and the conformity of distribution with a lake classification system was assessed (Lomnicky, unpublished manuscript; Liss et al. 1991). Forty-one lakes were assigned to six classification categories based on vegetation zone (forest, subalpine, alpine), elevation, and position relative to the west or east side of the crest of the Cascade Range. These classification variables represented fundamental characteristics of the terrestrial environment that indirectly reflected geology and climate. This geoclimatic perspective provided a broad, integrative framework for expressing the physical environment of lakes. Habitat conditions and macroinvertebrate distributions in study lakes were studied from 1989 through 1991. Distributions varied according to vegetation zone, elevation, and crest position, and reflected the concordance between habitat conditions and organism life history requirements. Habitat parameters affecting distributions included water temperature, the kinds of substrates in benthic microhabitats, water chemistry, and, to a limited extent, the presence of vertebrate predators. The number of taxa per lake was positively correlated with maximum temperature and negatively correlated with elevation. Forest zone lakes tended to have the highest number of taxa and alpine lakes the lowest. Substrates in nearshore microhabitats varied with vegetation zone. Organic substrates were more predominant than inorganic substrates in forest zone lakes. Organic substrates declined and inorganic substrates increased in the subalpine zone. There were virtually no organic substrates in alpine lakes. Taxa were placed into groups based on substrate preference. Ordinations indicated that the proportion of taxa in inorganic and organic-based substrate preference groups paralleled vegetation zone-substrate relationships. Lake water hardness and pH, as well as the presence of vertebrate predators affected the distribution of several taxa. Gastropods were limited to three forest lakes by their water hardness and pH requirements, and the dytiscid beetle, Potamonectes qriseostriatus appeared to be absent from forest lakes due, in part, to the pH requirements of this taxon. The distribution of three taxa (Taenionema, Ameletus, Desmona) appeared to be affected by the presence of vertebrate predators (salamanders and trout). Discriminant analysis was used to test the reliability of lake classification based on terrestrial characteristics. Discriminant analysis assigned lakes to categories based on similarities in kinds of substrates, substrate preference groups, and taxa. Strong concordance between both methods of lake classification supported the interconnection between terrestrial characteristics and processes and the abiotic and biotic conditions in lakes.
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