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Alysa J. Remsburg
Advisor: Monica Turner
PhD, 2007. Aquatic and Terrestrial Vegetation Influence
Lacustrine Dragonfly (order Odonata) Assemblages at Multiple Life
Stages
Understanding
how animals respond to habitat structure is a fundamental objective in ecology,
but is particularly challenging when the animals require distinct habitats
for different life stages. Although the majority of animals have spatially
segregated life stages, research on habitat associations has generally been
restricted to only one of the life stages. The relative importance of
aquatic and terrestrial habitat structure is not well known for the order Odonata
(dragonflies and damselflies).
In northern Wisconsin (USA) lakes, housing development contributes
to heterogeneity in riparian and littoral vegetation structure. I
surveyed odonate larval assemblages at 41 sites across 17 lakes. Based
on mixed-effects multiple regressions, model selection identified
site-level littoral macrophyte abundance as a key driver of larval
odonate species richness, and riparian wetland plant abundance
as the best predictor for odonate density. Subsequent field
experiments on larval predation and adult site selection helped
explain these patterns. Additional surveys of the most abundant
family (Gomphidae) at 22 lake sites indicated that local larval
densities depend most on recruitment, which I estimated from adult
densities during the previous year. Densities of emergent
Gomphidae skins (exuviae) were most related to densities of the
later-instar (second-year) larvae, further suggesting that larval
survivorship and movement are less variable spatially than recruitment
from the previous life stage.
Field experiments conducted at two South African lakes demonstrated
how riparian tree structures alter adult odonate abundances. Riparian
shade reduced the abundance of odonates at these potential breeding
sites. Perch structures, added to separate experimental plots,
supported locally higher adult abundances, but dragonflies were
not sensitive to perch structure density or diversity. Thus
shade is the critical habitat component that should be addressed
for odonate conservation in South Africa.
Collectively, this research describes the role of habitat structure
during multiple life stages. Field experiments demonstrate
that generalist predators are sensitive to vegetation structure. The
results suggest that riparian habitat selection by animals with
complex life cycles can influence aquatic communities.
MS, 2005. Amount, position and age of coarse wood
influence litter decomposition within and among young post-fire
Pinus contorta stands.
Spatial variation in vegetation and coarse wood is a major source
of forest heterogeneity, yet little is known about how this affects
ecosystem processes. In 15-yr post-fire Pinus contorta stands
of Yellowstone National Park, we investigated how decomposition
varies with coarse wood and other dominant structures within and
among stands. Tongue depressors (Betula sp.; TD) and litterbags
containing herbaceous litter (HL) and needles (NL) were deployed
for two years within three burned stands, and among 17 burned
stands and three mature stands (each 0.25-ha). Within stands,
decomposition varied among six microsite treatments (above and
below legacy wood, below logs on the ground and elevated logs,
below saplings, and on open soil). Two-year mass loss of all litter
types was least under elevated logs (HL 34.0%, NL 8.6%, TD 7.4%),
and greatest under legacy wood (HL 55%, NL 33%, TD 16%). Moisture
was also consistently lowest under elevated logs and highest beneath
logs on the ground. Among stands, two-year mass losses of HL and
TD were negatively related to amount of elevated wood. Slower
decay at stands with more coarse wood can influence carbon retention.
Coarse wood accumulation patterns remaining long after disturbances
influence litter decomposition within and among forest stands.
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