communities in a Laurentian watershed (Insecta; Ephemeroptera)

P. P. HARPERAND FRANCOISEHARPER Dkpartement de Sciences biologiques et Station de Biologie, Universitk de Montrkal, C.P. 6128, Succ. "A", Montrkal (QuC.), Canada H3C 3J7 Received October 8, 1981

HARPER,P. P., and F. HARPER.1982. Mayfly communities in a Laurentian watershed (Insecta; Ephemeroptera). Can. J. 2001. 60: 2828-2840. Mayfly communities were investigated in a series of four lakes, two beaver ponds, and 13 streams in a Laurentian watershed. Forty-five taxa were collected mostly through emergence trapping of adults (76 trap-years). Q and R analyses were used to show similarities between the stations and associations between the species. The middle reaches of the mainstream harbour the richest communities which are an assemblage of a few ubiquitous species (Baetis gr. pygmaeus, Stenonema modestum, Habrophlebia vibrans, and Paraleptophlebia volitans), lotic species (Baetisflavistriga, B. pluto, Stenonema vicarium; and Heptagenia pulla) some of which show a restricted distribution (Paraleptophlebia adoptiva, P. ontario, hebe, and interpunctatum heterotarsale), and also lentic species (Eurylophella verisimilis, Leptophlebia cupida, Cloeon simplex, C. rubropictum, Centroptilum album, and Stenacron interpunctatumfrontale). The headwater streams contain no distinct element, except perhaps Siphlonurus typicus, but rather the more resistant or dispersive species from the mainstream, mainly Ephemerellidae and Leptophlebiidae. The lower reaches of the mainstream are characterized by the addition of a few typical river species, Serratella sordida and vitreus. Lacustrine communities are less diverse, comprising mostly the lentic species from the streams plus a distinctive element (Stenacron interpunctatum canadense, Callibaetis ferrugineus, and Hexagenia limbata occulta). Only Leptophlebia cupida colonizes the bog lake, and no species occur in the beaver ponds. Most congeneric species are either spatially or temporally segregated. The sections of the mainstream produce an average of some 1000 adult /m2 per year; other streams are less productive and the lakes even less so (less than 100 /m2). The seasonal succession of the species and the emergence patterns of the dominant species are illustrated; a classification of emergence patterns is attempted on the basis of the present data and of other recent studies.

HARPER,P. P., et F. HARPER.1982. Mayfly communities in a Laurentian watershed (Insecta; Ephemeroptera). Can. J. 2001. 60: 2828-2840. Les communautCs d'EphCmCroptkres ont 6tC CchantillonnCes a l'aide de pikges d'Cmergence (76 pikges-annCes) dans un rdseau hydrographique des Laurentides constitu6 de quatre lacs, deux 6tangs de barrage de castors et 13 ruisseaux. On y a d6nombre 45 taxons. Des analyses en mode Q et en mode R ont permis de mettre en evidence les similaritCs entre les stations et d'Ctablir les associations d'espkces. Le cours moyen du ruisseau principal posskde les peuplements les plus riches constituCs d'espkces ubiquistes (Baetis gr. pygmaeus, Stenonema modestum, Habrophlebia vibrans, Paraleptophlebia volitans), d'espkces lotiques (Baetis flavistriga, B. pluto, Stenonema vicarium, Heptagenia pulla) dont certaines posskdent une distribution restreinte (Paraleptophlebia adoptiva, P. ontario, , Stenacron interpunctatum heterotarsale), ainsi que d'espkces lknitiques (Eurylophella verisimilis, Leptophlebia cupida, Cloeon simplex, C. rubropictum, Centroptilum album, Stenacron interpunctatum frontale). Les ruisseaux tributaires du cours supCrieur n'abritent pas d'espkces particulikres, a l'exception peut-&re de Siphlonurus typicus; ils sont plut6t colonisCs par les espkces les plus rksistantes ou les plus mobiles du cours principal, particulikrement des Ephemerellidae et des Leptophlebiidae. Le cours infCrieur du ruisseau principal est caractCris6 par l'addition de quelques espkces typiques des rivikres, Serratella sordida et Epeorus vitreus. Les communautCs lacustres sont moins diversifikes et se composent surtout des espkces lenitiques des ruisseaux, auxquelles s'ajoutent quelques espkces exclusives (Stenacron interpunctatum canadense, Callibaetis ferrugineus, Hexagenia limbata occulta). Seul Leptophlebia cupida colonise le lac tourbeaux et aucune espkce n'a CtC rCcoltCe dans les Ctangs de barrage de castors. On note une separation dans le temps ou dans l'espace de la plupart des espkces congCnCriques. Le cours principal du ruisseau produit environ 1000 Ephemkroptkres adultes /m2 par ann6e; les autres ruisseaux sont moins productifs et les lacs le sont trks peu (moins de 100/m2). La succession saisonni&redes espkces et les patterns d'kmergence des espkces les plus communes sont illustrks. A partir de ces resultats, il est possible d'esquisser une classification des patterns d'Cmergence chez les EphCmCroptkres.

Following the pioneering studies of McDunnough 1969) and in reports and theses (Pilon et al. 1975; (1925, 1930, 1932), the mayfly fauna of Quebec was Elouard 1977; Rochon 1977; Olivier 1980). one of the best known on the continent. Since then, only The present investigation was undertaken as part of a four papers deal specifically with the ecology of the local study of communities in a system of lakes and fauna (Harper and Magnin 197 1; Gibbs 197 1, 1977; streams in the Southern Laurentian Highlands of QuCbec Harper and Harper 1976), although additional informa- (Harper 1978). Emphasis is placed on the species tion is available in comprehensive studies (Mackay composition in the various habitats, the species distribu- 0008-4301 18211 12828-13$01 .00/0 01982 National Research Council of Canada/Conseil national de recherches du Canada HARPER AND HARPER 2829

tion, and their phenology. The study is based exclu- sively on adults which are well known taxonomically and can thus provide a precise picture of the com- munities. Methods Mayfly adults were collected through an extensive program of emergence trapping, some light trapping (black light GE F8T5/BL), and some general collecting (beating the ripar- ian vegetation, collecting swarms, checking spider webs). The emergence traps were of the design of Harper and Magnin (1971): a pyramidal frame covered with fibre-glass netting (7 threads/cm) which sampled an area of 0.5 m2; a sleeve fitted into one side allowed the removal of the with an aspirator connected to a hand-operated suction bulb. Traps set on the mainstream were emptied daily and those on the tributaries and the lakes three times a week during the entire emergence season, from early May to mid-September.

Identification and nomenclature follow Edmunds et al. Lac Moneses beaver dam (1976), but take into account the revisions of Bednaryk and "' emergence trap slle llghl trap s11e McCafferty (1 979), Allen (1 980), and Flowers (1 980). other collecllng slle Statistical procedures are taken from Legendre and Legen- mainstream sectlon dre (1979) and the data were processed on the UniversitC de MontrCal Cyber computer using the "Logiciel r" statistical package developed by Alain Vaudor. Sites were compared using both the Steinhaus and the chi-square similarity indices; the former bases similarity on the common possession of the same species in similar numbers (S = 2W/(A + B), where W is the sum of minimum abun- dances of each species in each sample pair, and A and B FIG. 1. Map of the study area and position of the sampling are respectively the sums of abundances of species in each stations. The numeration of the stations begins with the sample); the latter uses the proportions of each species as a mainsteam (1-30), and follows with the tributaries (a-m; basis for similarity irrespective of total numbers stations 31-52) and the lakes and ponds (53-73). The inset map of Quebec shows location of study area.

beaver ponds. The mainstream is thus divided into sections: where yil is the number of specimens of species i in site 1, yi. section I is a first-order stream, sections 11-IV are second the sum of all specimens of species i in all sites and y. 1 the sum order, and sections V-VI are third order. Thirteen tributary of all species in site 1. Clustering of sites resulted from streams (a-m) were also sampled and all are first order, except hierarchial intermediate (75%) linkage procedures. stream g which is second order for most of its length. Species associations were based on the Krylov (1968) Collections were also made on four lakes (Triton, Croche, similarity coefficient S = 1 - prob (x2), u = 1, with the Tracy, Geai) and two beaver ponds (Lac 2, Lac 3). Thus 73 exception that if (a + b)(a + c)/p 2 a, S equals 0; X2 is stations were sampled in the watershed (Table I), 68 of them calculated as p[l ad - bcl - (p/2)]2/(a + b)(c + d)(a + c)(b with emergence traps over one summer. Eight stations (9, 10, + d), where a, b, c, d are respectively the number of samples 12, 15, 20, 22 in mainstream section IV and 38 and 39 in where both species are present (a), one is absent (b, c), and tributary g) were sampled during two seasons. both are absent (d); p is (a + b + c + d). Clustering is based Descriptions of many of the sites have been given elsewhere on the nonhierarchial complete linkage procedure of Fager (Back and Harper 1-979; Harper and Cloutier 1979; Harper (1957), and the restrictions of Fager and McGowan (1 963) and 1980), so the general features are simply summarized in Table of Krylov (1968) have been taken into account. 1. The water is unpolluted, humic, soft, and slightly acid. The lakes generally freeze over from early November to early May. The study site Precipitation averages 5- 10 cm a month over the year and the The area chosen for this investigation is the upper Western winter snow accumulation is about 2-3 m. Water temperatures section of the L'Achigan River drainage (Fig. I), the site of are maintained between 20 and 25°C during the summer, with many of our previous studies on aquatic insects (Harper and a recorded maximum of 27°C. The surrounding vegetation is a Magnin 1971; Back and Harper 1979; Harper and Cloutier second-growth white birch (Betula papyrifera) association, a 1979; Harper 1980). It comprises a mainstream arising from successional stage leading to the sugar maple (Acer sac- Lac Pilon and flowing through a series of small lakes and charum) - yellow birch (B. lutea) climax of the area. CAN. J. ZOOL. VOL. 60, 1982

TABLE1. Summary of habitat conditions and sampling scheme. For each site, the corresponding station numbers are indicated, together with the frequency of collections where emergence traps were maintained. The numbers in the last column refer to individual stations

Frequency of Site Stations emergence trapping Habitat notes

- --- Mainstream I - Gravel, wood debris Mainstream I1 Three per week (1972) Gravel (2), silt (3), cobbles (4, 6), silt and ferns (5) Mainstream I11 Daily (1972) Mossy boulders (7), cobbles (8) Mainstream IV Daily (1972- 1973) Mossy boulders (10, 19), cobbles (9, 11-13, 21-24), sand and silt (14, 15, 18), backwater and weeds (17, 25) Mainstream V Daily (1972) Cobbles and gravel Mainstream VI - Boulders and cobbles Tributary a Gravel and silt Tributary b Irregular Gravel (32), silt (33) Tributary c Irregular Cobbles and gravel Tributary d Irregular Cobbles and gravel (intermittent) Tributary e Irregular Gravel (intermittent) Tributary g Daily (1972- 1973) Wood debris (38), gravel and sand (39-42) Tributary ga Daily (1973) Silt Tributary gb Daily (1 972- 1973) Gravel (44), silt (45) Tributary gc Three per week (1974) Silt and sand (intermittent) Tributary h Three per week (1974) Gravel (intermittent) Tributary i Three per week (1973) Cobbles (intermittent) (49), silt (50) Tributary k Gravel and cobbles Tributary m - Cobbles and gravel Lac Triton Three per week (1973) Pond, z, 3m Lac Croche Three per week (1974) Dimictic, vegetation scarce, z, z, 10m, hypolimnetic deoxygenation Lac Tracy Three per week (1974) Dimictic, vegetation abundant, z, z, 9m, deoxygenation Lac Geai Three per week (1974) Dimictic bog, z, 8m Lacs 3 and 4 Three per week (1978) Beaver ponds, bog and pond vegetation, z, 2m

Results a bisexual population in the lower mainstream, but the The mayfly fauna problem requires further investigation. Table 2 lists the 45 taxa collected during the study together with the numbers of specimens. It was not Distribution of the species possible to discriminate between the females of Baetis Thirty-nine taxa inhabit the mainstream (Table 3). pygmaeus and B. macdunnoughi; because the latter is Section I was sampled very irregularly and the low parthenogenetic at our latitude (Bergman and Hilsen- numbers reflect the sampling effort rather than the hoff 1978), it was assumed that when only females were species richness. The three middle sections (11-IV) collected in a station, such as in station 8, B. macdun- support some 20-30 species, a dozen or so of which are noughi was the only one present. On the other hand, abundant. The fauna is remarquably similar in all when the sex ratio was 1: 1, B .pygmaeus was considered sections and the dominant species are the same: Baetis to be dominant; in intermediate situations there was flavistriga, B . gr. pygmaeus, Heptagenia pulla, Ste- probably a mixture of both. Very few males of Ephe- nonema modestum, S. vicarium, Habrophlebia vibrans, merella invaria were collected: it is possible that the Paraleptophlebia volitans, and Eurylophella verisi- species is to some extent parthenogenetic. There is some milis. Only two species appear to be restricted to the indication, however, that two forms are involved, a uppermost stations: Paraleptophlebia debilis, a head- parthenogenetic population in the small tributaries, and water species, and Litobrancha recuwata, abundant in a HARPER AND HARPER

TABLE2. Species collected, all samples pooled

Males Females

Family Siphlonuridae Siphlonurus alternatus (Say) S. typicus Eaton Family Baetidae Baetisflavistriga McDunnough B. pluto McDunnough B. propinquus (Walsh) B. pygmaeus (Hagen) + B. macdunnoughi Ide Callibaetis ferrugineus (Walsh) C. skokianus Needham Centroptilum album McDunnough C. bellum McDunnough Cloeon rubropictum McDunnough C. simplex McDunnough Pseudocloeon sp. Family Oligoneuriidae Isonychia bicolor (Walker) Family Arthroplea bipunctata McDunnough Epeorus vitreus (Walker) Heptagenia pulla (Clemens) Leucrocuta hebe (McDunnough) Stenacron carolina (Banks) S. interpunctatum canadense (Walker) S. interpunctatum frontale (Banks) S. interpunctatum heterotarsale (McDunnough) Stenonema femoratum (Say) S. modestum (Banks) S. vicarium (Walker) Family Leptophlebiidae Habrophlebia vibrans Needham Leptophlebia cupida (Say) L. johnsoni McDunnough L. nebulosa (Walker) Paraleptophlebia adoptiva (McDunnough) P. debilis (Walker) P. guttata (McDunnough) P. mollis (Eaton) P. ontario (McDunnough) P. volitans (McDunnough) Family Ephemerellidae Ephemerella dorothea Needham E. invaria (Walker) Eurylophella prudentalis (McDunnough) E. temporalis (McDunnough) E. verisimilis (McDunnough) Serratella sordida (McDunnough) Family Caenidae Caenis simulans McDunnough Family Ephemeridae Hexagenia limbata occulta (Walker) Litobrancha recurvata (Morgan) CAN. J. ZOOL. VOL. 60, 1982

TABLE3. Numbers of each species collected from the six mainstream sections

Siphlonurus alternatus Baetis jlavistriga B. pluto B . propinquus B. gr. pygmaeus* Isonychia bicolor Callibaetis skokianus Centroptilum album Cloeon rubropictum C. simplex Pseudocloeon sp. Arthroplea bipunctata Epeorus vitreus Heptagenia pulla Leucrocuta hebe Stenacron carolina S. i. frontale S. i. heterotarsale Stenonema femoratum S. modestum S. vicarium Habrophlebia vibrans Leptophlebia cupida L. johnsoni Paraleptophlebia adoptiva P. debilis P. gutta ta P. mollis P. ontario P. volitans Ephemerella dorothea E. invaria Eurylophella prudentalis E. temporalis E. verisimilis Serratella sordida Caenis simulans Litobrancha recurvata No. of taxa Specimens/m2

*Includes B. pygmaeus and B. macdunnoughi, short muddy stretch (station 5). Section IV offers a wide restricted to the downstream stations on the mainstream, variety of habitats and it harbours the richest fauna. were however collected in some tributaries. Baetis propinquus and Eurylophella prudentalis repre- The tributary streams (Table 4) harbour fewer sent additional lotic elements in this section, and a species, and Siphlonurus typicus is the only additional number of lentic species, Callibaetis skokianus, Cen- taxon. The dominant species tend to differ from those of troptilum album, Stenacron i. frontale, Stenonema the mainstream and to vary from one stream to the next. femoratum, and Eurylophella temporalis, occur in the Small intermittent streams contain no species (stream quieter reaches. Epeorus vitreus and Serratella sordida gc) or only a few (streams a-e), none of which is appear only in the lowermost sections V and VI and abundant; Leptophlebiidae are most commonly encoun- represent the riverine species of the fauna. Paralepto- tered and may actually swim in from the mainstream at phlebia guttata and Ephemerella dorothea, which are high water in the spring. Intermittent stream h harbours HARPER AND HARPER

TABLE4. Numbers of each species collected from the tributary streams

abcde g ga gb h ikm

Siphlonurus typicus Baetis jlavistriga B. gr. pygmaeus Centroptilum album Arthroplea bipunctata Stenacron carolina S. i. frontale S. i. heterotarsale Stenonema modestum S. vicarium Habrophlebia vibrans Leptophlebia cupida Paraleptophlebia adoptiva P. debilis P. guttata P . mollis P. volitans Ephemerella dorothea E. invaria Eurylophella prudentalis E. temporalis E. verisimilis No. of taxa Specimens /m2

TABLE5. Species collected from lakes and ponds

Lakes Beaver ponds, Triton Croche Tracy Geai bog lacs 3 and 4

Siphlonurus alternatus Callibaetis ferrugineus Cloeon rubropictum C. simplex Stenacron i. canadense S. i. frontale Stenonema femoratum S. modestum S. vicarium Habrophlebia vibrans Leptophlebia cupida Eurylophella temporalis Hexagenia 1. occulta No. of taxa 8 9 8 1 0 Specimens /m2 17 56 14 100 - a large population of Siphlonurus typicus which sur- lakes Triton and Croche, is the largest of the tributaries, vives the summer drought in small permanent pools in and its fauna is similar to that of the mainstream; its own the stream bed. Tributaries i, k, and m are lake outlets tributary (station 43) contains an important population and never dry up completely, although the flow may be of the suspected parthenogenetic form of Ephemerella briefly interrupted, and their fauna tends to be more invaria. diverse than in other streams. Stream g, the outflow of Few species inhabit the lakes (Table 5) and many of 2834 CAN. J. ZOOL. VOL. 60, 1982 these also live in the slower reaches of the streams. -propinquus - are characteristic of the slower lotic stations, Three exclusive lake species, Callibaetis ferrugineus, as are loe eon rubropictum and Stenacron i. frontale Stenacron i. canadense , and Hexagenia 1. occulta, which also inhabit the lakes (respective Kyrlov coeffi- together with the lentic Cloeon spp., Stenacron i. cients 0.9966 and 0.9997, hierarchial grouping pro- frontale, Stenonema femoratum, and Eurylophella tem- cedure). poralis, make up the list of dominant taxa. The three Although the associations group only half of the larger lakes (Croche, Tracy, Triton) have relatively species, the species involved dominate the communities similar faunas and the numbers of species are of the and represent more than 86% of the specimens. same order. The large burrowing H. 1. occulta occurs The Q and R analyses represent different facets of the only in Lac Croche. The bog lake (Geai) contains only same phenomenon; there is indeed a concordance one species, Leptophlebia cupida, albeit in large num- between the clusters of stations and the species associa- bers. The beaver ponds contain no mayflies. tions. There is, for instance, a clear correspondence To assess the distribution of the species within the between the cluster of fast-water stations of the main- system, similarity and association matrices were con- stream and the largest species association (S. vicarium). structed from the 60 complete emergence series. The subgroup of the lower riffle in section IV is A Q-type analysis based on the Steinhaus and the characterized by the addition of a second association of chi-square coefficients reveals a number of clusters. (i) exclusive species (S. i. heterotarsale) . Most of the fast-water stations of section I11 (8) and IV The second cluster of lotic stations, the quieter (9-13, 15, 19-24) of the mainstream show a high reaches, has no special species association, but is degree of similarity (Steinhaus coefficient > 60%). On characterized by differences in proportions and num- the basis of the species composition only, regardless of bers. total numbers, two subgroups can be recognized, the The lake species form a distinct association of upper riffle stations (8- 15) and the lower riffle stations "exclusive" species (S. i. canadense, etc.), and a second (19-24) (chi-square coefficient > 0.988). (ii) At a "group" of nonexclusive species (C. rubropictum, S. i. similar level (Steinhaus coefficient > 60%), the slower frontale), but the lake stations show little overall stations of the middle section (15, 16), the upper (2, 3), similarity, probably because of the small populations and the lowermost sections of the mainstream (26-30), and the low number of species in each station. together with the stations (38-42) of the large tributary Distribution of the dominant taxa among habitats stream g form a distinct cluster. Here again on the basis along the mainstream stations is illustrated in Fig. 2. of the species composition alone, there is a discrimina- Four taxa, Baetis gr. pygmaeus, Stenonema modes- tion of the downstream stations (16,26,27,29) from the upper stations (chi-square coefficient > 0.987). (iii) Other stations show little evidence of similarity and clustering, except on a one to one basis. These are sites B gr pygmaeus with relatively few species, but with differing domi- S rnodestum () nances. The only exception is a clear cluster of the Lac Geai stations (66-69) which all contain only one same species. An R-type analysis of descriptors (species) reveals a few distinct species associations: (i) A large group of fast-water species, including Stenonema vicar- E verlslmll~s ium, S. modestum, Heptagenia pulla, Habrophlebia L CupIda H pulla vibrans, Paraleptophlebia volitans, P. ontario, Baetis B pluto gr. pygmaeus, B. Jlavistriga, B. pluto, and Eurylo- C rubroplctum phella verisimilis (Krylov coefficient = 0.98). (ii) A P ontarlo second smaller association, again of lotic species: L hebe Stenacron i. heterotarsale, Leucrocuta hebe, and Para- S t heterorarsale leptophlebia adoptiva (Krylov coefficient = 0.98). ( iii) B proptnquus An association of lake species (Krylov coefficient = P adopllva 0.98) composed of Stenacron i. canadense, Eurylo- c s~mplex phella temporalis, and Hexagenia 1. occulta. (iv) C album s I frontale Smaller associations of only two species are also apparent, but would not be retained on the basis of "the E lnvorla three species minimum criterion" of Krylov (1968). Two are mentioned anyway, as they appear to be of FIG.2. Distribution of the main taxa among stations in the some significance: Leptophlebia cupida and Baetis mainstream; r indicates riffles. HARPER AND HARPER 2835 turn, Habrophlebia vibrans, and Paraleptophlebia voli- waters than its congeners; Siphlonurus alternatus and tans, are ubiquitous, occurring in most habitats, al- Stenonema femoratum are typically lake species, while though with generally higher densities in the fast-water other Siphlonurus and Stenonema are lotic. In other areas. groups, little segregation is evident (Leptophlebia spp., The majority of species are restricted to riffles or are Paraleptophlebia spp., Eurylophella spp.), but tem- much more abundant there; these are Baetisjlavistriga, poral segregation is usually important. B. pluto, Stenonema vicarium, and Heptagenia pulla . Paraleptophlebia ontario , P . adoptiva, Leucrocuta Phenology hebe, and Stenacron i. heterotarsale also belong to the Figure 3 illustrates the emergence periods of the same group, but in section IV they are c&ously species collected in 1972 and 1973. The seasonal restricted to the lower riffle (stations 20-24) and nearly succession begins in mid-May, and new species con- absent elsewhere. tinue to appear into August. There is no true autumnal The slow regions are characterized by an assemblage element, although Paraleptophlebia debilis starts of Eurylophella verisimilis, Leptophlebia cupida, emerging after the stream temperatures have begun to Cloeon simplex, C. rubropictum, Centroptilum album, decrease. The onset of the emergence was generally Baetis propinquus, and Stenacron i. frontale. delayed in 1972 by comparison with 1973, particularly In most respects, Fig. 2 reveals graphically the same in the early and late species, but the emergence sequence species associations and the same habitat distributions as is roughly the same for both years. the numerical indices used in the Q and R analyses, thus Figures 4 and 5 represent respectively for 1972 and confirming these results. 1973 the emergence patterns of the dominant species, as Many congeneric species are spatially segregated: for illustrated by data from a station in which each was instance, Stenacron i. frontale in lakes and the slow abundant. Paraleptophlebia adoptiva, Leptophlebia streams, S. i. canadense in lakes, and S. i. heterotarsale cupida, Eurylophella invaria, Habrophlebia vibrans, in fast streams; Baetis propinquus inhabits slower and P. ontario typically have a short emergence which corresponds to Corbet's (1964) and Harper and Mag- nin's (1971) "synchronous" type. The other species have an emergence of the "extended" type: in some, L cup~da P odopt~vo such as Stenonema modestum, Eurylophella verisimilis, B gr pygmaeus , S vlcarlum C skolr~anus S madestum -5 L nebuloso = S femoratum J- E ver~s~mll~s r- S I heterotarsale ---, B flavlstrlga -- E lnvarla E prudental~s -F L johnsan~ e B macdunnmgh~(8) x 832 -- - S typ1cus - ,v-- - L hebe A b~punctata r - B pygmaaus (12) H v~brans e S I conodense - S vlcarlum (21) t--L3 -- S carol~no E ~nvarla(29) 4. H pullo - E ver~s~rn~l~s(17) A- I b~color - L recurvata S modestum (9) ---- E vltreus -r S I frontole B flavlstr~ga(12) P vol~tons - H pulla (2 1) B proplnquus - E temporolls - S sord~do e- B pluto p C album P moll1s -I C rubrop~ctum C s~mplex - B proplnquus (17) H l occulto - C rubrop~ctum(17) E daratheo - B pluto (23) Pseudocloean sp + P antorlo P P guttoto '7 S alternotus 1c3 C ferrug~neus o P debtl~s a C stmulons d C bellum I FIG.4. Representative emergence patterns of major species I I I 1 1 in 1972; station numbers are indicated in parentheses. The FIG. 3. Seasonal succession of the species based on a upper part of each graph represents males, the lower part pooling of all collections; dark bars represent the 1972 data, females. The lack of data in late June is due to the disruptions white bars the 1973 data. caused by Humcane Hazel. CAN. J. ZOOL. VOL. 60, 1982

running-water habitats where the primitive species live and where they reach their greatest diversity among the manifold available habitats. Few groups are restricted to lakes, and indeed most of the lentic species can also inhabit the slower sections of streams.

B pygmoeus (10) '++--- -v+- Density The average yield of 1000 to 1200 adults /m2 per year in some stream stations is higher than usual, particularly if the maximum yield of 2816 in trap 15 is taken into S modestum (12) L account. Sprules (1947) in a similar system records a maximum of 3604 (as 3037 /yd2 (1 yd = 0.9 14 m)) and Ide ( 1940) collected up to 6500 /m2 in southern Ontario. Indeed in our own stream, during a previous study (Harper and Magnin 197 1) up to 6032 mayflies /m2 were H pulla (12) recorded. More commonly, values of the order of S I frontale (19) 300-1500 (in several German and Austrian streams H v~brans(13) (lllies 197 1,1978,1980; Sandrock 1978)), 600 (Oregon (Kraft 1964)), and 300 (Alberta (Boerger and Clifford B proplnquus (19) +' -.-A C rubrop~ctum(18) 1975)) are encountered. In lakes, yields are usually El pluto (12) much lower and our results are particularly so, but this P ontorlo (19. 20) +--- C s~mplex(25) may be a general characteristic of the unproductive P deb~l~s(50) *&- Laurentian lakes. Comparative values from other areas include 40/m2 in Lake Heming (Flannagan and Lawler FIG. 5. Representative emergence patterns of major species 1972), 423/m2 in Dundas Marsh (Judd 1953), 80- in 1973; station numbers are indicated in parentheses. The upper part of each graph represents males, the lower part 800/m2 in oligotrohic Lake Paaj Wi(Paarsivirta 1975), females. and 392-2635 /m2 in a small Scottish loch (Morgan and Waddell 1961). Such values, while indicative of the and Baetis jlavistriga, most of the population emerges productivity of a water body, are subject to much within a fortnight, but with a few stragglers over the variation from year to year, by a factor of up to seven following weeks or even months. In species such as (Illies 1978). Stenonema vicarium , Heptagenia pulla , Stenacron i. BClanger (1978), who compared bottom samples of frontale, Paraleptophlebia volitans, and Cloeon rub- nymphs (taken by conventional methods) and our ropictum, the emergence is spread over many weeks emergence trap yields in 1973, calculated an average without any definite mode except perhaps at midemer- standing crop of nymphs which was smaller than the gence. Finally in some species of Baetis, the extension yield of adults by a factor of two; Ide (1940) had made of the emergence seems to be related to polyvoltinism: similar observations in southern Ontario. These discrep- three distinct peaks occur in Baetis pygmaeus and B. ancies are no doubt due to the still inadequate sampling macdunnoughi, and two in B. pluto. methods for immatures or, to some extent, the migration Generally the patterns for the same species for both of mature nymphs prior to emergence. The mean years are similar and the differences can be related to standin crop reported for mayflies in the Holarctic is particular weather conditions. Cool temperatures in 375/m 8 and the maximum is 1448 (Clifford 1980). May 1972 (Back and Harper 1979) led to the late appearance of the early species (P. adoptiva, L. Species zonation cupida), but also to a more synchronized emergence. On The distinction between stream and lake species is the other hand, the cool wet summer of 1972 obscured well documented; however, a large number of lentic the patterns of the later emerging species, particularly species inhabit both the littoral areas of lakes and the the polyvoltine B. pygmaeus and B. pluto. slower reaches of streams. There does not appear to be a distinct headwater fauna Discussion in this instance, except for Siphlonurus typicus in stream Species richness h and Paraleptophlebia debilis in a few others. This Our record of some 40 stream species and a dozen may be due to the fact that the streamlets we investigated lake species fall within the order of magnitude of other are either the outlets of small lakes and ponds, or similar inventories (Sprules 1947; Oliver and Danks runoff-fed streams; none is truly spring fed. In the 1975). Evidently, mayflies are primarily adapted to spring-fed West Creek on Mont Saint-Hilaire in south- HARPER AND HARPER 2837 em Quebec, Mackay (1969) found a very typical fauna found in the upper riffle. Given the proximity of the two of nine species (mainly Ameletus spp., Paralepto- riffles (about 400 m) and their overall physiographical phlebia moerens, Ephemerella dorothea, Eurylophella similarity, the situation of the upper riffle as a lake outlet jhneralis) only one of which occurs in our streams, in is doubtless of significance; lake outlets have long been small numbers. By contrast, the fauna of our headwater recognized as special habitats with a specialized com- streams is composed essentially of the most tolerant or munity (Illies 1956). dispersive species of the mainstream, particularly Ephe- Temporal segregation merellidae, Leptophlebiidae, and Baetidae, with the Most congeneric species are temporally segregated, addition of species characteristic of temporary habitats, for instance the various species of Stenonema (vica- such as Arthroplea bipunctata; Bogoescu and Rogoz rium, modestum) and of Paraleptophlebia (adoptiva, (1973) noted a similar faunal assemblage in Balkan volitans, ontario, debilis), and the species and cohorts streamlets. Needham (1928) suggested that, as a rule, of Baetis (pygmaeus , JIQvistriga , propinquus, pluto) . small streams are most productive in benthic inverte- This is generally the case in mayflies, but exceptions brates per unit area than larger streams; this is probably have been reported (Langford 1975). Many congeners incorrect when headwaters are taken into account, and are also spatially segregated; this is the case of the three Sprules (1947) and Kamler (1962) have shown that subspecies of Stenacron interpunctatum which behave middle-sized streams are most productive. here as true species. The lower reaches of the mainstream appear poorer and the number of species decreases despite the addition Emergence types of riverine elements, such as Serratella sordida and From investigations in the same stream system, Epeorus vitreus. Harper and Magnin ( 1971) postulated that emergence The bog Lac Geai supports a large population of patterns in mayflies fell into two fundamental types. Leptophlebia cupida, its sole mayfly species. A More recent studies and the present data allow us to similar situation occurs in European bogs, where Lepto- update this discussion. (i) There is a very distinct spring phlebia vespertina is the equivalent species (McLachlan fauna composed of univoltine and semivoltine species and McLachlan 1975). Both species are ubiquitous and (and the early cohort of some polyvoltine species) which capable of supporting the humic and acid waters (Bagge emerge soon after the water warms up in the spring. and Salmela 1968). Typically their emergence is very synchronous, espe- Neither of the two beaver ponds harboured any cially in climates with well-marked seasons such as mayflies; this is somewhat unexpected, since Sprules ours. Paraleptophlebia adoptiva and Leptophlebia (1947) had shown that the darning of a stream by beavers cupida are perfect examples. (ii) The summer species had caused a marked reduction in the mayfly popula- must first complete their nymphal growth and start tions, but not their elimination. On the other hand, this emerging in early and midsummer; their emergence may be a phenomenon common to older beaver ponds pattern tends to be more dispersed, probably because which are depauperate in some taxa (G. Pritchard, water temperatures are then more stable. This group is University of Calgary, personal communication). far from homogenous and distinctions are necessary. The other lakes support similar faunas; despite the The more characteristic species start to emerge near or small numbers collected, there appear to be differences after the summer solstice, during the period of maxi- in the frequencies of the species between the lakes, and mum water temperature. The environmental conditions some species are restricted to a particular lake (e.g., are stable and the emergence is spread over a long period Hexagenia 1. occulta in Lac Croche). with a maximum near the middle of the period. Paraleptophlebia volitans belongs here. Spatial distribution Also included are species exhibiting a pattern inter- The distribution of the species among the various mediate between the two types: the emergence is habitats (Fig. 3) and the comparison of the stations on extended, but the maximum occurs early. This appears the basis of their respective faunas provide a picture to be the case in our data on Stenonema modestum (see which is in accord with the present knowledge of the however data in Harper and Magnin (1971) showing a environmental requirements of the species (Leonard pattern with a central maximum). 1965; Bergman and Hilsenhoff 1978; Flowers and There is the particular case of species which, although Hilsenhoff 1978). The only unusual feature is the univoltine, show a distinct bimodal pattern, viz., Isony- difference observed between the two riffles in main- chia bicolor in Harper and Magnin (197 1). Such is also stream section IV; indeed the lower riffle harbours large the case of Ameletus inopinatus in Great Britain in populations of species (Paraleptophlebia adopttva, which two cohorts are separated by an interruption of Leucrocuta hebe, and Stenacron i. heterotarsale) not hatching during the winter (Gledhill 1959). A division 2838 CAN. J. ZOOL. VOL. 60, 1982 of the population into cohorts has been used to explain chronous and the extended patterns reflect two different complex growth or emergence patterns in species which life-history strategies and, particularly if they are related otherwise appear to be univoltine; in some instances, in some way to population density, they become tendencies towards polyvoltinism are demonstrated. parameters of significant ecological interest. The European Ecdyonurus torrentis and the North American Stenacron interpunctatum are thought to complete the growth of three cohorts in 2 years (Harker Acknowledgments 1952; McCafferty and Huff 1978). This study was supported by the Natural Sciences and There are further the polyvoltine species which are Engineering Research Council of Canada and the Fonds spring species for their first generation, then complete Formation des chercheurs et action concertee (FCAC). one or more summer generations, such as Baetis We thank Daniel Roy, Louise Cloutier, Christian Back, pygmaeus and B. macdunnoughi. Others undergo only Josee Thibault, and Rene Rochon who participated in summer generations, e. g ., Baetis pluto. In the simplest the maintenance of the emergence traps. Pierre Legen- situation, the cohorts and generations are discrete and dre and Alain Vaudor provided the statistical advice. successive, but in recent analyses many species have been shown to possess overlapping cohorts, for instance Baetis lutheri and B. alpinus in Austria which can ALLEN,R. K. 1980. Geographic distribution and reclassifica- mature 10- 11 cohorts in 30 months (Humpesch 1979). tion of the subfamily Ephemerellinae (Epherneroptera: Furthermore, under special circumstances, polyvoltine Ephemerellidae). In Advances in Ephemeroptera biology. species can become univoltine (Illies and Masteller Edited by J. F. Flannagan and K. E. Marshall. Plenum Publishing Corp., New York. pp. 7 1-91. 1977); in our stream, Baetis jiavistriga is univoltine, BACK,C., and P. P. HARPER.1979. Succession saisonnikre, while in Wisconsin it is said to be bivoltine (Bergman Cmergence, voltinisme et rCpartition de mouches noires des and Hilsenhoff 1978). Laurentides (Diptera; Simuliidae). Can. J. Zool. 57: 627- Finally there are the autumnal species which start 639. emerging when both photoperiod and temperature are BAGGE,P., and V. M. SALMELA.1968. The macrobenthos of declining, such as Paraleptophlebia debilis. Autumnal the River Tourujoki and its tributaries (Central Finland). 1. species are little affected by climatic conditions and Not. Entomol. 58: 159-168. emerge in a similar pattern each year (Thibault 1971). BEDNARYK,A. F., and W. P. MCCAFFERTY.1979. Biosys- The maximum occurs early in the emergence period, but tematic revision of the genus Stenonema (Epherneroptera: a late maximum is described for Paraleptophlebia Heptageniidae). Can. Bull. Fish. Aquat. Sci. 201: 1-73. BBLANGER,D. 1978. L'entomofaune d'un ruisseau des guttata (Carlson 1973). Laurentides (St-Hippolyte) et Cvaluation de trois mCthodes Emergence in mayflies is thus more plastic than d'Cchantillonnage. MCmoire de maitrise, UniversitC de would appear at first glance and much could be gained Montrkal, MontrCal, P. Q. from the accumulation of additional data from areas BERGMAN,E. A., and W. L. HILSENHOFF.1978. Baetis different from the cold temperate regions where most (Ephemeroptera; Baetidae) of Wisconsin. Great Lakes studies have been conducted up to now. Patterns may Entomol. 11: 125-135. even vary from one site to the next in the same area for BOERGER,H., and H. F. CLIFFORD.1975. Emergence of the same species (for example, Siphlonurus lacustris in mayflies (Epherneroptera) from a northern brown-water Norway (Brittain 1979)). stream of Alberta, Canada. Verh. Int. Ver. Theor. Angew. There is also an indication in Brittain's (1979) data Lirnnol. 19: 3022-3028. BOGOESCU,C., and I. Ro~oz.1973. Consideratii ecologice that there may be an inverse relation between the asupra larvelor de efemeroptere raspindite in unele izvoare synchrony of the emergence and the density of the local din bazinul riulu Oltet. Hidrobiologia, 14: 2 17-224. population; Sprules' (1947) data on Paraleptophlebia BRITTAIN,J. E. 1979. Emergence of Ephemeroptera from debilis point to the same phenomenon. This is certainly Ovre Heimdalsvatn, a Norwegian sulalpine lake. Proceed- worth investigating. ings of the 2nd International Conference on Ephemeroptera. Variations in the emergence patterns of individual pp. 115-123. species over a wide geographical gradient are poorly CARLSON,P. H. 1973. Seasonal distribution of mayflies known; Habrophlebia vibrans which in our stream (Epherneroptera) from Wildcat Creek, Pickens County, possesses one of the shortest and most synchronous South Carolina. Proceedings of the 1st International Con- emergences has an extended emergence of some 13- 17 ference on Ephemeroptera. pp. 205-208. CLIFFORD,H. F. 1980. Numerical abundance values of mayfly weeks in South Carolina (Carlson 1973). nymphs from the Holarctic region. In Advances in Ephem- Emergence patterns thus reflect the overall success eroptera biology. Edited by J. F. Flannagan and K. E. and strategy of the species and cannot be studied Marshall. Plenum Publishing Corp., New York. pp. 503- irrespective of the other life-cycle features. The syn- 509. HARPER AND HARPER 2839

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