From: ASSESSMENT OF SPECIES DIVERSITY IN THE MIXEDWOOD PLAINS ECOZONE
DRAGONFLIES AND DAMSELFLIES
P. M. Catling, R. Hutchinson and B. Ménard
4. STATISTICS
4.1 TOTAL ODONATE BIODIVERSITY
Odonate diversity, in terms of number of species, tends to increase as climates become warmer and wetter. It is not surprising therefore that the southernmost ecozone in Canada contains a large portion of the total diversity of this group, both within Canada and within the provinces in which the ecozone is situated. In fact the 157 species documented in the Mixedwood Plains is 78 % (157 of 202) of the species reported for all of Canada, and 93 % (157 of 169) of the species reported for all of Ontario and Quebec. It is also an impressive number on a broader temperate scale since 80 species have been reported for British Columbia (Cannings and Stuart 1977) and 45 for Great Britain and Ireland (Hammond 1983). Worldwide it has been estimated that there are approximately 5000 species of damselflies and dragonflies.
4.2 RARE AND SIGNIFICANT SPECIES
Although the species in the ecoregion are relatively well known their status is unknown in many cases. This applies particularly to the dragonflies of rivers and small streams, as well as to some northern species of bogs and fens. With increasing study over the past few decades, a number of species thought to be very rare, such as Neurocordulia yamaskensis, Lanthus parvulus, Stylogomphus albistylus, and Stylurus spiniceps, have proved to be simply uncommon or local.
Approximately 25 species are known from less than 20 localities in the ecozone, and some are known from less than 5, but in many of these cases, a species is suspected of a much broader occurrence, as for example with Aeschna clepsydra, A. tuberculifera, Gomphus adelphus, G. borealis, G. descriptus, Stylurus scudderi, and Williamsonia fletcheri. Recent information on the ecology of some of these species as well as increasing ability to identify the nymphs will probably result in many more localities being discovered. Williamsonia fletcheri for example breeds in small sphagnum bog pools, sometimes little more than water-filled holes where a rotted spruce left a space in the moss (eg. Charlton and Cannings 1993). Such small habitats may have seemed inconsequential as breeding sites to many field biologists. While some species, such as Williamsonia fletcheri may prove to be more abundant than currently known, the species of bogs and fens (Lestes eurinus, Nehalennia gracilis, Williamsonia fletcheri, Somatochlora spp.) are still likely to be rare in the Mixedwood Plains because of the limited bog and fen habitats that are available and the continuing destruction of these special habitats.
Thirty-eight species are considered rare enough to warrant tracking in Ontario by the Natural Heritage Information Centre (Holder & Sutherland 1998, see Table 1). All but one of these, the western Coenagrion angulatum, are present in the Mixedwood Plains. Not only do almost all of the rare species occur in the Mixedwood Plains, approx. half of them do not occur in any other Canadian ecozone. Species evidently confined to the Mixedwood Plains include Aeshna mutata, Anax longipes, Argia apicalis, A. sedula, A. tibialis, A. translata, Celithemis fasciata, Dromogomphus spoliatus, Enallagma basidens, E. traviatum westfalli, Gomphus quadricolor, G. vastus, G. viridifrons, Hetaerina americana, H. titia, Ischnura hastata, Lestes disjunctus australis, Libellula vibrans, Macromia taeniolata, Perithemis tenera, Stylurus plagiatus, Sympetrum ambiguum, Tramea carolina and T. onusta (boldface indicates species tracked by the Ontario Natural Heritage Information Centre).
Ophiogomphus anomalus, Stylurus notatus and Tachopteryx thoreyi are considered very rare generally (Bick 1983, Orr 1992). The former is a species of clear rapid rivers (eg. Daigle 1988, Burke 1995) whereas the latter flies up and down tree trunks around sunny hillside seepages in deciduous woodland (eg. Barlow 1991), and is not adequately documented inthe ecozone (Savard 1987). Stylurus notatus occurs on large rivers (Fig. 5), and although widespread, appears very local. Enallagma clausum is probably more common in Ontario than the few current records suggest. It is included in the ecozone on the basis of records from Blainville, Lachine and Rigaud.
Some of the rare species are peripheral, occurring mainly to the south of the ecozone and wandering northward, and possibly not breeding within the ecozone (eg. Tramea spp.). Other peripheral species, common to the south, are confined in Canada to the ecozone where there are localized, well established breeding populations. Examples include the species of Zygoptera such as Argia sedula, A. tibialis, and A. translata.
4.3 EXCLUDED TAXA
Based on single reports, Erythrodiplex berenice, Hetaerina americana, Somatochlora linearis and Tachopterix thoreyi (Savard 1987) are excluded from Quebec (and Canada in the case of T. thoreyi) on the basis of lack of recent reports.
