- 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with a lake classification system was assessed (Lomnicky, unpublished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.