The Dragonflies
(Insecta: Odonata)
of the Columbia Basin, British Columbia:
Field Surveys, Collections Development and Public Education
Biogeography and Faunal Elements
Dragonfly species may be grouped with others
that share similar distributions to form what can be termed faunal
elements. The majority of the 66 species known from the Columbia
Basin are restricted to North America (Nearctic Region), although
six are holarctic, and are defined here as species with transcontinental
ranges in both North America and Eurasia. Two species (Anax junius
and Sympetrum corruptum) are known from eastern Asia but
do not have holarctic distributions. This section describes the
Nearctic faunal elements found in the Columbia Basin (species with
holarctic distributions are also assigned to a North American faunal
element). This discussion is summarized in the list in Appendix
2. The faunal elements are:
1. Boreal (21 species, 32%). Species
occurring in the northern spruce (Picea) forests, across
the boreal zone from treeline to the southern margin. In general,
these species range from the Atlantic Provinces across the northern
New England states, Quebec, northern Ontario, parts of the northern
tier of mid-western states, the Prairie Provinces north of the Great
Plains, and northern British Columbia, often ranging considerably
southward in the higher mountains and plateaux of the western Cordillera.
These species can be further subdivided into:
i. Widespread Boreal (13 species,
20%). With ranges as described above.
Coenagrion resolutum, Enallagma boreale, E. cyathigerum
(also Holarctic), Aeshna eremita, A. juncea (also
Holarctic), A. sitchensis, A. subarctica (also Holarctic),
Cordulia shurtleffi, Somatochlora albicincta, S.
franklini, S. whitehousei, Leucorrhinia hudsonica,
Sympetrum danae (also Holarctic).
ii. Northern Boreal (1 species, 1.5%).
Species that are common near the northern treeline, but that are
virtually absent from the northern contiguous United States and
from the southeastern Atlantic Provinces, and do not extend far
south into the Cordillera. Only one species from this element,
Coenagrion interrogatum, has been collected.
iii. Southern Boreal (6 species, 9%).
Species that are uncommon north of 60º N in the West and absent
near the Arctic treeline in the East, but range far down the Cordillera
and/or into the southeastern Atlantic Provinces and New England
states. Some (e.g. Aeshna interrupta) are common on the
Great Plains. Nehalennia irene, Aeshna interrupta,
Somatochlora cingulata, S. minor, S. walshii,
Leucorrhinia proxima.
iv. Western Boreal (1 species, 1.5%).
Species not found east of Hudson Bay. Leucorrhinia borealis.
2. Transition (15 species, 23%). Species
generally most common in the southern boreal forests and adjacent
montane forests in the West, and mixed and deciduous forests in the
East. Calopteryx aequabilis, Enallagma ebrium, Aeshna
canadensis, A. constricta, A. tuberculifera, A.
umbrosa, Gomphus graslinellus, Epitheca spinigera,
Somatochlora forcipata, Leucorrhinia glacialis, L.
intacta, Libellula julia, Sympetrum costiferum,
S. internum, S. obtrusum. 3.
Cordilleran (11 species, 17%). Species confined to the western
mountains and their intervening valleys and plateaux. Argia emma,
A. vivida, Ischnura cervula, Aeshna californica, A. palmata, Ophiogomphus
occidentis, Stylurus olivaceus, Cordulegaster dorsalis, Macromia
magnifica, Somatochlora semicircularis, Libellula forensis.
4. Western (7 species, 10%). Species
confined to west of the 100th meridian, but otherwise ranging widely
in North America. Amphiagrion abbreviatum, Ischnura perparva,
Ophiogomphus severus, S. madidum , S. occidentale.
5. Austral (6 species, 9%). Species
ranging across the continent south of the boreal forests, often
extending into Transition areas, but with most of the range in the
United States. Lestes forcipatus, Enallagma carunculatum, Anax
junius, Libellula lydia, L. pulchella, Sympetrum vicinum.
6. Widespread (6 species, 9%). Species
with broad distributions in North America, from north to south and
east to west, overlapping several of the other elements listed.
These species range into boreal regions to varying degrees. Lestes
congener, L. disjunctus, L. unguiculatus, L. dryas (also Holarctic),
Libellula quadrimaculata (also Holarctic), Sympetrum corruptum.
The faunal elements are thus represented in the Columbia
Basin as follows:
21 species of Boreal origin (32%) are recorded. Of these, 13 (20%)
are Widespread Boreal, 6 (9%) are Southern Boreal, 1 (1.5%) is Northern
Boreal and 1 (1.5%) is Western Boreal. Transition species total
15 species (23%) and there are 11 (17%) Cordilleran species. Seven
species (10%) are Western, 6 (9%) are Austral and 6 (9%) are Widespread
according to our definitions.
Six species Lestes dryas, Enallagma cyathigerum,
Aeshna juncea, A. subarctica, Libellula quadrimaculata and
Sympetrum danae are holarctic, ranging around the Northern Hemisphere.
It is likely that these species have had such wide distributions
since before the last glacial age. In contrast to the situation
in some other insect groups, there is no evidence that the Beringian
glacial refugium influenced the distribution of British Columbian
Odonata. The only odonate with a Beringian distribution, Somatochlora
sahlbergi Tryböm, does not range south of the central Yukon
(Cannings and Cannings 1997). There, however, it hybridizes with
two close relatives widespread in the Montane Cordillera: S.
albicincta and S. hudsonica (Cannings and Cannings 1985).
The Columbia Basin is part of the Montane Cordillera
Ecozone, which includes all the southern Interior of B.C. north
to roughly the northern end of Williston Lake. Farther north in
the Cordillera, 70 percent of 33 species in the Yukon are of Boreal
origin (Cannings and Cannings 1997); in the Montane Cordillera Ecozone
this boreal component is reduced to 34% of 77 species, about the
same as in the Columbia Basin (33% of 66 species). This reduction
is the result of the strong influence of more southerly faunas,
since all but one (Somatochlora kennedyi Walker) of the Yukon's
boreal species range south into the Montane Cordillera.
Five boreal species: Aeshna septentrionalis Burmeister,
Ophiogomphus colubrinus Selys, Somatochlora hudsonica (Selys),
S. septentrionalis (Hagen) and Leucorrhinia patricia
Walker, are known from the Montane Cordillera Ecozone, but are yet
to be found in the Columbia Basin. Eighteen species in the Boreal
element of the Columbia Basin range south of 51º N along the mountains
and plateaux of the Cordillera: Coenagrion resolutum, Enallagma
boreale, E. cyathigerum, Nehalennia irene, Aeshna eremita, A. interrupta,
A. juncea, A. sitchensis, A. subarctica, Cordulia shurtleffi, Somatochlora
albicincta, S. cingulata, S. minor, S. walshii, Leucorrhinia borealis,
L. hudsonica, L. proxima and Sympetrum danae. These also
could be termed boreomontane species.
In contrast, two species of the Boreal element are
scarce as far south as even the northern parts of the Kootenays:
Coenagrion interrogatum and Somatochlora whitehousei.
These species are also sparsely distributed further to the north
relative to their numbers east of the Cordillera. Their rarity in
the west is probably more related to habitat scarcity rather than
to limited post-glacial colonization.
Since the last glacial age, the Columbia Basin has
been recolonized by Odonata from at least two southern refugia:
one in what is now the southeastern United States and another in
the intermontane Cordillera south of Canada. The putative species
pairs Somatochlora albicincta/S. hudsonica and Leucorrhinia
hudsonica/L. borealis have distribution patterns that suggest
this history. S. albicincta and L. hudsonica are boreal
species with transcontinental ranges. Presumably they inhabited
the southeastern refugium and recolonized the Columbia Basin from
the east and north, following the early retreat of the continental
ice sheet east of the Rocky Mountains. S. hudsonica and L.
borealis have similar distributions, but do not range east of
Hudson's Bay, indicating that they recolonized the Cordillera from
the southwest. S. hudsonica has yet to be recorded from the
Columbia Basin, but certainly occurs there.
From 10,000 to 8,000 years before present, following
the retreat of the Cordilleran glaciers, the climate became warmer
in the region than it is today (Hebda 1995). Presumably, although
there is no fossil evidence, southern, warm-adapted species ranged
more widely to the north than they do at present. Disjunct, present-day
populations in isolated, unusually warm habitats offer evidence
for these former distributions.
For example, Ischnura damula Calvert is apparently
now restricted in the Cordillera to the Liard River Hot Springs.
Argia vivida, in a genus known for its Neotropical origins
(Pritchard 1991), is largely associated with geothermally heated
streams in the Columbia Basin and elsewhere in British Columbia
(Pritchard 1982). It, too, perhaps, was more widespread during the
warmer hypsithermal period and has subsequently been restricted
to warm sites (Pritchard 1989).
Patterns of distribution between the Pacific Maritime
and the Montane Cordillera ecozones require more study. In Washington
State, several species considered completely coastal in British
Columbia, such as Ischnura erratica, Sympetrum illotum
and Pachydiplax longipennis, also occur east of the Cascade
Mountains. The Columbia River Valley may have acted as a corridor
for these coastal species to range inland. In addition, a number
of interior species, such as Archilestes californica McLachlan,
Erpetogomphus compositus Hagen and Gomphus lynnae
Paulson, do not range north of the Columbia Basin in central Washington
(Paulson 1997). This area is the northern limit of distribution
of many plants and animals. In contrast, Argia emma, which
ranges at least as far east in the Interior as Christina Lake, is
also locally common in the lower Fraser River Valley of British
Columbia on the western side of the Coast Mountains. It has apparently
colonized this area by using the Fraser River Valley as a conduit
from the Interior valleys of the Thompson and Okanagan drainages.
It is not known from coastal habitats in Washington State, although
it is common east of the Cascades there.
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