Henri Goulet. 1998. Sawflies (Hymenoptera: Symphyta) in Smith, I.M., and G.G.E. Scudder, eds. Assessment of species diversity in the Montane Cordillera Ecozone. Burlington: Ecological Monitoring and Assessment Network, 1998.

SAWFLIES
(HYMENOPTERA: SYMPHYTA)

Henri Goulet

MAJOR DISTRIBUTION PATTERNS

In Appendix A, there is a list of all sawfly species. For all known species, their distribution in ecoregions is recorded. The most striking aspect is the very unequal sampling of sawflies among these ecoregions. Some have none (ecoregions 198 and 199), or very few ( 201, 203 and 206), and a few are acceptably sampled (205, 209 and 214). Basically, the northern two thirds of the ecozone are barely sampled while most efforts went into thenational parks of southern Alberta and central British Columbia. Thus, it is almost impossible to compare the fauna of each ecoregion in any meaningful way. The detail survey of each region is hardly started, and sampling needs to be intensified in all ecoregions. Based on my experience, knowledge of the flora, climate, and topography, I suspect that most regions should have more than 150 species. To avoid this problem, I have organized the data into a different set of roughly defined regions stressing major distribution patterns.

Table 2. Heading codes: 1= Pacific coast to at least Quebec; 2=Cascades and eastward to at least Manitoba; 3= Rockies to Pacific coast, and north and south of ecozone; 4= as 3, but from southern portion of ecozone and southward; 5= in ecozone and north and south of ecozone, but not east and west of it; 6= as 5, but in northern portion of ecozone and northward; 7= as 5, but in southern portion of region and southward; 8= restricted to Cascades and southward; 9= restricted to Rockies and southward;109= in foothills of Rockies and northward; 11= eastern edge of region at low elevation.

Table 2 is a summary of the main types of distribution for species of our area. Three types of distributions were not recorded among native species: southern stray species, regular southern migrants, and species endemic to the Montane Cordillera Ecozone. The most common range type is the transamerican range from the Pacific coast to at least Quebec (24% of species), then with ranges extending from the Pacific coast to the eastern edge of the ecozone in its southern portion (16% of species). Of the native species recorded 42 (17%) of species are found in Canada only in the Montane Cordillera Ecozone. This is a very significant value as it represents about 5% of all Canadian species not found anywhere else in Canada. Other distribution patterns types are less prevalent. About 7% of species occur from the Cascades and eastward, from the Pacific coast widely over the mountainous regions of western North America, and from the very eastern edge of the ecozone at low elevation and eastward. About 2% of species are not occurring east and west of the ecozone, but are recorded north and south of it, or not found east or west of the ecozone, but mainly north of it,and along the Cascades as far north as Manning Provincial park.

There are some unusual distributional patterns discovered, but not evident in the ecoregions. Much of it is associated with the eastern ecoregion (207 and 214). As mentioned before there is an extremely narrow band of typical eastern North American species reaching the very edge of the ecozone. Most of these species have been recorded as far west and south as forested regions west of Calgary. Some of these species may have disjunct ranges along the eastern slopes of the Colorado Rockies. An overlooked pattern is found along the Alberta foothills as far south as north of the Corwsnest Pass. This is the tundra corridor. I have found several species of vascular plants as well as ground beetles following this very narrow distribution pattern. In winter time many kilometres east of the divide, the snow cover is thin, and consequently the ground is very cold. Thus, only extremely cold hardy species survive there. South of Crownest Pass, there is no tundra adapted species found except for a few species with disjunct range in the highest mountains of Colorado. In ecoregion 210, another interesting pattern emerges. It is that of species with a range extended along the Cascades from northernmost California. Some of the species found could not be found further north such as Garibaldi Provincial Park which occur just west of the ecozone. Another interesting pattern exemplified by ecoregions 211 and the dry parts of 209 are the Great Basin have a few species of sawflies adapted to dry and hot conditions.

Table 2 gives important clues about the general pattern of interglacial re-invasion of the basin. As the climate in our region became warmer, the icesheet retreated, and open tundra-like vegetation developed. Sawflies probably moved in from the south. West of the Rockies, sawflies were probably alpine and subalpine in origin, but east of the divide, they were probably of alpine as well as tundra origin. This reflect the faunal composition seen today at high elevations in the ecozone. With warmer climatic conditions, forest developed. These forests and their associated fauna was partly of cordilleran origin west of the Rockies at least in the south of the ecozone and of boreal and montane origin in the north of the ecozone, and east of the Rockies this flora and fauna was of boreal and to a lower extent of montane origin. The boreal fauna is not from the Beringian refugium but from south of the icesheet based on geographical variants studied in sawflies and ground beetles(Goulet, 1986). However, there is an evidence for some Beringian elements invading the ecozone from the north. The range of Tenthredo olivacea probably expanded southward along mountain ranges up to the northermost reaches of the ecozone. With the increased warm trend more species moved in from the south with boreal, montane and tundra-like flora moving up in the mountains. Thus, coastal insects and plants reached our ecozone either from the eastern slopes of the Cascades via the Columbia valley between Oregon and Washington, or from low mountain passes along the coastal mountains (e.g., the Prince Rupert to Terrace valley). Many species of sawflies (63 species) are found today in the ecozone and along the Pacific coast. Other species, mainly found in the southern portion of the ecozone, but not east or west of it, probably came from the Great Basin region. First, forest associated species came from the south, then during the warmest trends, a few sawflies adapted to the dry conditions found in the prairie and subdesertic ecoregions (part of 213, 210 and 209 and most of 210) became established. On the eastern edge of the ecozone a few cold hardy eastern species finally extended to the ecozone. Finally, with the arrival of European colonists on the Pacific coast, species of sawflies were accidentally introduced. Some of these became established in the ecozone. However based on records, there is no evidence that they dominate as seen in the Mixed Wood Plain Ecozone (Goulet, 1996b) in Eastern Canada.