Abstract:
This thesis explored the distributions and life histories of dragonflies and
damselflies (Insecta: Odonata) of the riverine wetlands of the Willamette Valley
in western Oregon, USA. Odonate species distributions were characterized over
two seasons in the autumn of 2000 and the spring of 2001-at twenty-seven
wetlands located throughout the valley. Distributions of nymphs and adults were
compared with wetland habitat conditions that may affect odonate diversity.
Odonate nymph and adult distributions were analyzed through
Hierarchical Agglomerative cluster analysis (HA). HA identified discrete
clusters of sites based on the distributions of species in the genera Aeshna,
Erythemis, Lestes, Libellula, Pachydiplax, Sympetrum and Tramea. To identify
habitat associations with odonate species, nymph and adult data were analyzed
by Non-metric Multidimensional Scaling (NMS). NMS revealed that odonate
distributions are associated with site hydrology, water depth and temperature, the
presence of large emergent plants (e.g. Typha latifolia), the presence of fish, and
surrounding landcover. These data will provide guidance for wetland managers
in the use of odonates as indicators of wetland health.
To further examine the relationship between odonate species and their
wetland habitats, quantitative life history data for the 27 odonate species were
analyzed to determine functional associations between species attributes and the environments in which they are found. Oviposition location, presence of a
resting egg, over-wintering life stage, nymphal foraging strategy and adult flight
season were subjected to NMS, to determine biological similarities between
species occupying particular locations. Life history patterns correlated strongly
with hydrology. Analysis of sites by odonate species ricimess found a
relationship between richness and site hydrology, but failed to explain the
distribution of several species associated with wetlands that dry during part of
the year. We conclude from our results that species-level life history data are
essential for explaining odonate distributions.
We determined that the presence of odonate species in a wetland is
indicative of habitat condition, that analysis of odonate distributions at the
species level is necessary to understand habitat associations, and that analysis of
life-history attributes provides a functional understanding of odonate
distributions that measurements of species richness or the distributions of generaor families alone cannot explain.
