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The xeric hypothesis is that bees are more abundant pollinators than anthophilous flies in dry, temperate biomes, and the habitat filtering hypothesis is that differences in the proportions will impact plant community composition because different pollinators favour different floral traits. However, few studies have examined the predictive value of these hypotheses. In particular, differences in plant-pollinator compositions within biomes, such as the Prairie Ecozone, have not been compared. We documented plant-pollinator interactions and plant abundance in three Canadian prairie types. Flower visits in moist tall grass prairie were mainly by flies in the Syrphidae, whereas visits in the drier fescue and mixed grass prairie were mainly by long-tongued bees in the Apidae. Short-tongued bee visits were not significantly different between the prairie types. Insect visits to tubular, zygomorphic, violet/blue-, and white-flowered plants were higher in drier fescue and mixed grass prairie than in moister tall grass prairie. Further, proportions of plants with these features were lower in the tall grass prairie. Thus differences in the proportion of flies and long-tongued bees, likely affected by habitat conditions including moisture levels, appear to be influencing the types of plants that dominate each prairie type, providing some support for these hypotheses. Key words: functional groups, habitat filtering, moisture gradient, plant-insect interactions, pollination, prairie. L'hypothese xerique propose que les abeilles soient des pollinisateurs plus abondants des biomes secs et temperes que les mouches anthophiles, et l'hypothese du filtrage de l'habitat propose que les differences dans les proportions aient un impact sur la composition des communautes vegetales, car les differents pollinisateurs favorisent differents caracteres floraux. Toutefois, peu d'etudes ont examine la valeur predictive de ces hypotheses. En particulier, les differences des compositions plantes-pollinisateurs a l'interieur des biomes tels que l'ecozone des Prairies n'ont pas ete comparees. Les auteurs ont documente les interactions plantes-pollinisateurs et l'abondance de vegetaux dans trois types de prairies canadiennes. Les visites des fleurs de la prairie humide a grandes graminees etaient principalement effectuees par les mouches appartenant aux Syrphidae, alors que les visites dans la prairie a fetuque plus seche et dans la prairie a graminees mixtes etaient principalement effectuees par les abeilles a langue longue appartenant aux Apidae. Les visites par les abeilles a langue courte n'etaient pas significativement differentes d'un type de prairie a l'autre. Les visites par les insectes de plantes a fleurs tubulaires, zygomorphes, violettes/bleues et blanches etaient plus frequentes dans la prairie a fetuque plus seche et la prairie a graminees mixtes comparativement a la prairie plus humide a grandes graminees. Par ailleurs, les proportions de plantes possedant ces caracteristiques etaient plus faibles dans la prairie a grandes graminees. Ainsi, les differences dans la proportion de mouches et d'abeilles a langue longue, probablement affectees par les conditions de l'habitat, dont les niveaux d'humidite, semblent influencer les types de plantes qui dominent chaque type de prairie, apportant un certain appui a ces hypotheses. [Traduit par la Redaction] Mots-cles : groupes fonctionnels, filtrage de l'habitat, gradient d'humidite, interactions plantes-insectes, pollinisation, prairie., Introduction The xeric hypothesis (Michener 1979) is that bees are more common pollinators in temperate, xeric habitats than in cool arctic or humid tropical habitats. This is based on the [...]

In Canada, silky prairie-clover (Dalea villosa var. villosa (Nutt.) Spreng) is a nationally rare plant, growing only in sand dunes in Saskatchewan and Manitoba. Previous research indicates that this species is incapable of self-pollination, making it dependent on insect pollinators for successful reproduction. The insect visitor community to D. villosa in Spruce Woods Provincial Park (SWPP), Manitoba, was documented and compared with that of 13 co-flowering plants that share some of its insect visitors. In total, 29 insect taxa were observed feeding on nectar or pollen from D. villosa. Hymenoptera were the most frequent visitors, comprising 60.7% of the taxa and making 93.5% of all visits. The visitation rate per stem to D. villosa (0.0042 stems x [min.sup.-1]) was the second highest of all of the plants with which it was compared. The insect visitor diversity was 4.0 (Simpson's reciprocal index), and the constancy index was 0.72. The high visitation rate, diversity, and constancy to this species may be due to a lack of competition for pollinators. Over half of the insect visitor taxa (54%) and visits (68%) were by omnivorous insects, as opposed to herbivorous ones. This means that there is interconnectivity between a mutualistic network involving D. villosa and several antagonistic networks. Key words: antagonistic network, insect visitation rate, mutualistic network, rare plant, pollination. Au Canada, la dalee soyeuse (Dalea villosa var. villosa (Nutt.) Spreng) constitue une plante rare a l'echelle nationale, venant seulement dans des dunes de sable en Saskatchewan et au Manitoba. Les recherches antecedentes indiquent que cette espece est incapable d'autopollinisation, la rendant ainsi dependante d'insectes pollinisateurs pour reussir sa reproduction. On a documente la communaute d'insectes visiteurs sur le D. villosa dans le parc provincial Spruce Woods, au Manitoba et on l'a comparee a celle de 13 especes fleurissant sur le meme site, partageant certains des insectes visiteurs. Au total, on a observe 29 taxons d'insectes se nourrissant du nectar ou du pollen du D. villosa. Les visiteurs les plus frequents sont des hymenopteres comportant 60,7 % des taxons effectuant 93,5 % de toutes les visites. Le taux de visite sur les tiges du D. villosa (0,0042 tige par minute) est le second plus frequent pour l'ensemble des plantes comparees. La diversite des insectes visiteurs est de 4,0 (index reciproque de Simpson) et l'index de constance de 0,72. Le taux eleve de visites ainsi que la diversite et la constance chez cette espece pourraient etre attribuables a l'absence de competition pour les pollinisateurs. Plus de la moitie des taxons des insects visiteurs (54 %) et des visites (68 %) representent des insectes omnivores, comparativement aux herbivores. Ceci signifie que la presence d'interconnectivite entre un reseau mutualiste impliquant le D. villosa et plusieurs reseaux antagonistes. [Traduit par la Redaction] Mots-cles: reseau antagoniste, taux de visite par des insectes, reseau mutualiste, plante rare, pollinisation., Introduction When a plant has been identified as being rare, conservation plans to help the species recover are typically prepared (Demauro 1994). However, an inadequate understanding of the factors affecting [...]

Pollination facilitation can occur when plant species share pollinators. Whether facilitation occurs depends on the flowering period overlap (synchrony), number of shared insect visitors (similarity), quantity and quality of insect visits, and the subsequent impact on seed production. Western Silvery Aster (Symphyotrichum sericeum (Vent.) G.L. Nesom) is a rare, selfincompatible plant visited by a wide range of generalist insect species. There are 22 common plant species that may facilitate insect visitation to the rare plant by supporting shared pollinators. Plant species with low synchrony and high similarity with S. sericeum are potential facilitators. In contrast, plant species with high synchrony and similarity likely act as competitors as the aggregative response to increasing plant density was saturating, suggesting that synchronously flowering species do not increase insect visitations. Hymenoptera responded more strongly than Diptera to increases in flowering stem density. These data suggest that facilitation of insect visitation between plant species via a numerical response that extends the flower season is possible but not likely via an aggregative response. Restoration of S. sericeum may therefore be more successful if potentially facilitating plants are grown with it; further testing of the impact of potential facilitators on seed production in S. sericeum is required. Key words: facilitation, insect visitation, pollination, sequential mutualism. La pollinisation peut etre facilitee lorsque des plantes partagent leurs pollinisateurs. L'expression de cette facilitation depend de la periode de recouvrement (synchronie), du nombre d'insectes visiteurs partages, de la qualite et de la quantite des visites par les insectes et de l'impact subsequent sur la production de semences. L'aster argente de l'ouest (Symphyotrichum sericeum (Vent.) Nesom est une plante rare autocompatible visitee par une large gamme d'especes d'insectes generalistes. Il y a 22 especes de plantes pouvant faciliter la visite des insectes cette plante rare en supportant une pollinisation partagee. La faible synchronisation des especes de plantes et la grande similitude avec le S. sericeum pourraient faciliter la pollinisation. Au contraire, les especes de plantes montrant de fortes synchronisations et similarites sont susceptibles d'agir comme des competiteurs puisque la reaction agregative pour augmenter la densite des plantes se trouve saturante, suggerant que les plantes a floraisons synchrones n'augmentent pas les visites des insectes. Les hymenopteres reagissent plus fortement que les dipteres dans l'augmentation de la densite des tiges forales. Ces donnees suggerent que la facilitation des visites d'insectes entre les especes de plantes via une reaction numerique etalant la saison de floraison est possible, mais peu susceptible de survenir via une reaction agregation. La restauration du S. sericeum pourrait consequemment etre plus efficace si des plantes capables de facilitation sont cultivees avec elle; on doit conduire d'autres essais sur l'impact des facilitateurs potentiels pour la production des gaines chez le S. Sericeum. [Traduit par la Redaction] Mots-cles: facilitation, visite des insectes, pollinisation, mutualisme sequentiel., Introduction Much of pollination research has focused on how plants compete with each other for the attention of pollinators (Levin and Anderson 1970; Knight et al. 2005). Less studied is [...]

Flower-visiting insect activity to the rare Symphyotrichum sericeum (Vent.) G.L. Nesom and the common Solidago nemoralis Ait. var. longipetiolata (Mack. & Bush) Pal. & Steyerm. was examined to detect compositional and temporal similarities, A hand pollination experiment was conducted to determine whether pollen was limiting seed set. Of the 31 insect taxa that visited these plants, Bombus bifarius Cresson was the most common visitor to both species. More insect visitors of the Halictidae and Bombyliidae were received by S. sericeum than S. nemoralis, which received more visitors of the Syrphidae and Tachinidae. The insect visitation rate was not significantly different between the two plant species. Solidago nemoralis was visited by fewer insect taxa per day than S. sericeum, but the constancy of its visitors was higher. The insect visitor composition changed over time, with B. bifarius ignoring S. sericeum plants initially, then visiting them more frequently as the number of receptive S. nemoralis capitula declined. Hand pollination increased seed set in the earliest flowering capitula of S. sericeum, but not for those flowering during the peak. This research shows that the quantity of insect visits to the rare plant is comparable with that of the common plant but that pollination quality may be lower, particularly for early blooming capitula. Key words: insect constancy, insect visitation rate, pollinator competition, rare plant, seed set, tall-grass prairie. Afin de deceler des similarites temporelles on de composition, les auteurs ont examine les activites d' insectes visiteurs sur les fleurs de l'espece rare Symphyotrichum sericeum (Vent.) G.L. Nesom et l'espece moins rare, le Solidago nemoralis Ait. var. longipeliolata (Mack. & Bush) Pal. & Steyerm. L'auteure a conduit une experience de pollinisation manuelle pour determiner si le pollen limite la mise a graine. Sur les 31 taxons d'insectes visiteurs, le Bombus bifarius Cresson est le plus frequent sur les deux especes. Plus d'insectes visiteurs appartenant aux Halictidae et Bombyliidae ont ete accueillis par le S. sericeum que le S. nemoralis. celui-ci ayant recu plus de visiteurs appartenant aux Syrphidae and Tachinidae. Le taux de visite par les insectes ne differe pas significativement entre les deux especes de plantes. Le Solidago nemoralis recoit moins de taxons visiteurs par jour que le S. sericeum, mais la Constance de ses visiteurs est plus grande. La composition en insectes visiteurs change avec le temps, le B. bifarius ignorant les plants du 5, sericeum au depart, pour les visiter plus frequemment a mesure que le nombre de capitules du S. nemoralis diminue. La pollinisation manuelle augmente la formation de graines dans les capitules a floraison halive du S. sericeum, mais pas dans ceux venanl au maximum de la floraison. Cette recherche montre que le nombre de visiles par les insectes sur la plante rare se compare a celui de la plante plus commune, mais que la qualite de la pollinisation pourrait etre plus faible. stirtotit en debut de floraison. Mots-cles: Constance des insectes, taux de visile des insectes, competition entre pollinisateurs, plante rare, mise a graine, prairie a herbes hautes. [Traduit par la Redaction], Introduction The reasons why some plants are rare can be difficult to ascertain, but reproductive difficulties are a common cause (Kwak and Bekker 2006). Low seed production in a plant [...]

Tall-grass prairie is endangered by habitat loss and fragmentation, and climate change. Flower-visiting-insect activity on two tall-grass prairie communities, one larger and more mesic than the other, was examined to determine network structure, and temporal and spatial variation. Flower-visiting insect richness and visitation rate were monitored for 2 years. Most insect-visitor taxa were Diptera, followed closely by Hymenoptera. Only 18% of insect taxa visited both communities in both years, but were responsible for 70% of all visits. The three most active insect species were Toxomerus marginatus Say, Bombus ternarius Say, and Odontomyia pubescens Day. The core plants, receiving over 67% of all visits, were Solidago canadensis L., Solidago rigida L., and Zizia aptera (Gray) Fern. Seasonal differences in insect visits were primarily due to temperature, as well as normal phenological patterns. Diptera was more abundant at one site, likely owing to differences in the quantity of nearby aquatic larval habitat. The mutualistic network of these two tall-grass prairies is significantly nested, which may make it more resilient to environmental perturbations than systems that are more compartmentalized. Key words: Diptera, flower visitors, Hymenoptera, insect visitation rate, nestedness, tall-grass prairie. La perte et la fragmentation de l'habitat, ainsi que le changement climatique, menacent la prairie d'herbes hautes. L'auteur a examine l'activite des insectes visitant les fleurs dans deux communautes d'herbes hautes, l'une plus grande et plus mesique que l'autre, afin de determiner la structure du reseau, et la variation spatio-temporelle. Il a suivi la richesse en insectes visiteurs des fleurs et le taux de visites au cours de deux annees. Les Dipteres constituent la majeure partie des taxons visiteurs, suivis de pres par les Hymenopteres. Seulement 18 % des taxons d'insectes ont visite les deux communautes au cours des deux annees, mais comptent pour 70 % des visites. Les Taxomerus marginatus Say, Bombus ternaries Say et Odontomyia pubescens Day representent les trois especes les plus actives. Les Solidago canadensis L., Solidago rigida L. et Zizia aptera (Gray) Fern. forment le groupe principal de plantes recevant 67 % des visites. La temperature ainsi que les patrons phenologiques normaux modulent les differences saisonnieres des visites par les insectes. La plus grande abondance de Dipteres sur un des sites s'explique par les differences dans la quantite d'habitats aquatiques voisins pour les larves. Le reseau mutualiste de ces deux prairies d'herbes hautes est significativement implante, ce qui devrait le rendre plus resiliant aux perturbations environnementales que les systemes qui montrent une plus forte fragmentation. Mots-cles : Dipteres, visiteurs des fleurs, Hymenoptere, taux de visite par les insectes, implantation, prairie d'herbes hautes. [Traduit par la Redaction], Introduction The tall-grass prairie is one of the most endangered ecosystems in Canada, with less than 3% of the original prairie remaining in Ontario and less than 1 % in [...]

To provide a more accurate assessment of the rarity of the plant genus Corispermum (Amaranthaceae), commonly known as bugseeds, in Manitoba, 1 undertook a survey of all historical populations. In total, 68 quarter sections were selected for presence/ absence surveys; 37 of them contained at least one species of bugseed. Only 10 of the 20 historical populations in Manitoba were relocated. The total estimated size of known bugseed populations in Manitoba in 2010-2011 was approximately 9 820 to 13 060 individuals. American Bugseed (C. americanum (Nutt.) Nutt. var. americanum) is the most abundant and widespread of the bugseeds in Manitoba, followed by Hairy Bugseed (C. villosum Rydb.). There is only one population of Hooker's Bugseed (C. hookeri Mosyakin var. hookeri) in the province. Pallas' Bugseed (C. pallasii Steven) was not relocated and should probably be considered extirpated in Manitoba. The habitats at 61% of the localities where bugseeds were confirmed are anthropogenically disturbed, the most common habitat being roadsides with exposed bare sand. Of the localities where bugseeds were not relocated, 67% occurred in natural sandy areas, suggesting that dune stabilization is a major threat to the continuing persistence of these species. [ABSTRACT FROM AUTHOR]