TEMPORAL AND SPATIAL CHANGES: RECENT TRENDS

Carabid beetles were poorly sampled in Canada before Lindroth began his field work in the late 1940s. For that reason, it is difficult to assess changes in species abundance. Some species, considered as rare in the past, are commonly collected today; in many cases, the apparent rarity was due to the lack of habitat knowledge. The best example is that of Platypatrobus lacustris . Darlington (1938) originally described the species from a single female. A few additional specimens were discovered in collections, but the species continued to be considered as a great rarity, until Goulet (1965) discovered that it lives exclusively in beaver houses. The species is now commonly found in beaver houses in the Mixedwood Plains Ecozone and elsewhere. Another factor responsible for the apparent recent abundance of some species is the use of more effective collecting techniques, such as pitfall traps, Berlese funnels, sifters, and light traps. Pterostichus lachrymosus Newman is mainly associated with maple groves in southern Ontario and Québec. Until the 1970s, the species was rarely collected in Canada (see Lindroth 1966: 495); however, it was quite commonly caught in pitfall traps during ecological studies in the Laurentides, Québec, in the 1970s and 1980s (Trudel-Levesque 1971; Bousquet 1986). Several small carabids, such as Perigona pallipennis LeConte and Badister parviceps Ball, were unknown or poorly collected in Canada until the use of Berlese funnels and sifters. In Canada, Pentagonica picticornis Bates was known in the 1960s by only three specimens (Lindroth 1969); although the habitat of the species is still unknown, the species has been collected in several localities in southern Ontario and Québec at light or with light traps.

As far as I know, there are no carabid species inhabiting the Mixedwood Plains Ecozone that were abundant in the past and are considered as rare today. There are also no cases of species disappearances due to man-induced activities. However, some ecologically specialized species or species with restricted geographical range in the Ecozone, could be considered as threatened. This is the case of Pterostichus diligendus Chaudoir and Bembidion basicorne Notman, restricted in Canada to the Appalachian Mountains in the extreme southern Québec. Chlaenius purpuricollis Randall is restricted to alvars; Pterostichus castor Goulet and Bousquet and Platypatrobus lacustris Darlington live only in beaver houses. Residential development and the associated loss of ecological niches are more likely to threaten these species than those with wider ecological tolerance. Although no Carabidae present in the Mixedwood Plains Ecozone are placed on the official list of endangered and threatened wildlife and plants in North America (Anonymous 1991), a few beetles inhabiting southern Canada are listed. This is the case of the Staphylinidae Lorditon niger Gravenhorst that lives in old growths of deciduous forest, an habitat that has disappeared from most of eastern North America. Only seven specimens of this species have been collected since the 1940s (Campbell 1982).

Spence and Spence (1988) reported that Pterostichus melanarius (Illiger), a European species introduced in North America, had a negative influence on the native Pterostichus adstrictus Eschscholz in British Columbia. Both species occur in the Mixedwood Plains Ecozone although P. adstrictus is rarer than P. melanarius ; the available information, although fragmentary, does not suggest that one species had an influence on the other one. There is no documented case of changes in species abundance for Carabidae in eastern Canada due to the introduction of an exotic species. To the contrary, it seems that the introduction of exotic species in Canada has generally enriched the carabid fauna of anthropogenic habitats (Spence and Spence 1988).

Because carabids were poorly sampled in the past, it is also difficult to evaluate extensions or reductions in species ranges. Dicaelus teter Bonelli is a large, apterous species that was collected at several locations in the Ottawa region (Hull, Old Chelsea, Ottawa) at the beginning of this century. The species reaches its northern distributional limits in this area and is otherwise known in Canada only from southern Ontario. Despite its conspicuousness and extensive collecting in the Ottawa region, the species has not been found since the 1940s. The urban development, quite extensive in the area, may be responsible for the destruction of the habitat required by the species.

There are a few relatively well documented cases of recent range expansions of carabids to the Mixedwood Plains Ecozone. Some cases are discussed here. I know of no species that expanded its range southward.

1. Eastern expansions. Some western species have recently spread into the Mixedwood Plains Ecozone. Bembidion bifossulatum , was known by 1960 only from western Ontario and westward; it is now known from southern Ontario, the Montréal region and eastward up to the Chicoutimi region in Québec (Larochelle 1975). Bembidion rupicola , known only from Manitoba and westward in the 1950s (Lindroth 1963) has been found in southern Ontario since the mid 1970s (Bousquet 1987). Bembidion obscurellum is a small but conspicuous carabid commonly found from the Pacific region to the prairies. The species was first collected east of Manitoba in 1947 in western Ontario (Lindroth 1963: 339); in 1964 it was found in the Montréal area, Québec (Lindroth 1969), in 1965 in Vermont (Lindroth 1969), in 1977 in New Brunswick (Bousquet 1987), and in 1985 in Newfoundland (Bousquet 1987). We don't know if the species was accidentally introduced in the Montréal area in the 1960s from the west or if it spreaded naturally eastward and was overlooked in Ontario.

2. Northern expansions. The only well documented case of a northward expansion is that of Harpalus puncticeps , an introduced species. The species was introduced in the mid 1950s in Long Island, New York (Dietrich 1957; Lindroth 1968). By the end of the 60s and in the 70s, the species was recorded from mainland New York, Vermont (Davidson 1975), and Maine (Duval and Duval 1977). By the mid 80s, the species occurred in southern Québec, southern Ontario (Bousquet 1987), and Nova Scotia (two specimens in the Canadian National Collection of Insects); it is now relatively common at least in southern Ontario.

   There are several species, previously unknown from Canada, that have been collected recently in southern Ontario, particularly along the shore of Lake Erie (e.g. Dyschirius haemorrhoidalis Dejean, Clivina dentipes Dejean, Elaphropus capax LeConte, Perigona pallipennis LeConte, Harpalus indianus Csiki, Anisodactylus dulcicollis LaFerté-Sénectère, Anisodactylus laetus Dejean, Stenocrepis cuprea Chaudoir, and Lebia analis Dejean). Several of these species are probably stragglers, carried to the shore by winds and waves, and are probably not established in the country. Some may have been overlooked in the past, apparently because of their small size. However, other species, such as Platynus opaculus LeConte, are probably examples of genuine northern range expansions. The species is a relatively large platynine living in the same general habitat as other members of Platynus in Canada. It was known only south of the border, but by the mid 60s and early 70s, it was collected in several localities in southern Ontario and southern Québec. It is unlikely that the species was overlooked previously in Canada.

3. Western expansions. The only examples of westward migration toward the Mixedwood Plains Ecozone are those of introduced species. This is the case of Amara aulica Panzer, a rather large amarine found in open places, which was known in North America in the early 1960s only from Newfoundland and Nova Scotia (Lindroth 1968: 666). By the mid 60s, the species was established in the Montréal area. Bembidion bruxellense Wesmael, Agonum muelleri Herbst, and Amara bifrons Gyllenhal, are examples of European species, first introduced in Newfoundland, that have subsequently spread westward into mainland Canada and northeastern United States.

There is no doubt that long-term studies are essential for monitoring temporal and spatial changes in species abundance and in community composition. Such studies are lacking for carabids. There are several sites in southern Québec and southern Ontario that are suitable for biodiversity monitoring studies. Two of these are of particular interest. One is Rondeau Provincial Park located along the north shore of Lake Erie in southern Ontario. The site includes a great variety of habitats. The carabid community of the area is fairly well known since the site was visited by several beetle collectors since the 1960s and was extensively collected for beetles in 1985 by members of the Biosystematics Research Centre (now Eastern Cereal and Oilseed Research Centre). The fact that the area is protected should facilitate long-term monitoring. In term of biodiversity, this site is one of the richest protected area in the Mixedwood Plains Ecozone.

The second site is at Rigaud, about 60 km west of Montréal, Québec. The area is rich in habitats particularly along the Ottawa River and on the mont Rigaud, the northern part of which has been bought and is being preserved (Goulet, pers. comm.). Since the 1960s, the locality has been extensively sampled for carabid beetles and at least 260 species have been recorded (Larochelle 1975).

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