Pollination success of animal-pollinated flowers depends on rate of pollinator visits and on pollen deposition per visit, both of which should vary with the pollen and nectar "neighborhoods" of a plant, i.e., with pollen and nectar availability in nearby plants. One determinant of these neighborhoods is per-flower production of pollen and nectar, which is likely to respond to environmental influences. In this study, we explored environmental effects on pollen and nectar production and on pollination success in order to follow up a surprising result from a previous study: flowers of Ipomopsis aggregata received less pollen in years of high visitation by their hummingbird pollinators. A new analysis of the earlier data indicated that high bird visitation corresponded to drought years. We hypothesized that drought might contribute to the enigmatic prior result if it decreases both nectar and pollen production: in dry years, low nectar availability could cause hummingbirds to visit flowers at a higher rate, and low pollen availability could cause them to deposit less pollen per visit. A greenhouse experiment demonstrated that drought does reduce both pollen and nectar production by I. aggregata flowers. This result was corroborated across 6 yr of variable precipitation and soil moisture in four unmanipulated field populations. In addition, experimental removal of pollen from flowers reduced the pollen received by nearby flowers. We conclude that there is much to learn about how abiotic and biotic environmental drivers jointly affect pollen and nectar production and availability, and how this contributes to pollen and nectar neighborhoods and thus influences pollination success.

Nectarivorous hummingbirds subsist almost exclusively on a mixture of sucrose, glucose and fructose found in floral nectar. Previous studies have shown that hummingbirds can fuel hovering flight almost exclusively using recently ingested sucrose. However, the relative capacities for the direct utilization of glucose and fructose by hovering hummingbirds remain unknown. 13C-enriched solutions of glucose and fructose were administered separately. Exhaled breath samples were collected using feeder-mask respirometry and sent for subsequent mass spectrometric analysis. I found hovering hummingbirds transition from exclusively oxidizing endogenous fatty acids when fasted, to oxidizing newly ingested carbohydrates when given access to either glucose or fructose solutions. Interestingly, the amount ingested, fractional turnover of stable carbon isotope signatures, amount oxidized, energy expended and proportion of hovering metabolism supported by each hexose, were each similar between glucose and fructose. These results demonstrate hovering hummingbirds’ ability to utilize fructose and glucose equally.

Nectarivorous hummingbirds subsist almost exclusively on a mixture of sucrose, glucose and fructose found in floral nectar. Previous studies have shown that hummingbirds can fuel hovering flight almost exclusively using recently ingested sucrose. However, the relative capacities for the direct utilization of glucose and fructose by hovering hummingbirds remain unknown. 13C-enriched solutions of glucose and fructose were administered separately. Exhaled breath samples were collected using feeder-mask respirometry and sent for subsequent mass spectrometric analysis. I found hovering hummingbirds transition from exclusively oxidizing endogenous fatty acids when fasted, to oxidizing newly ingested carbohydrates when given access to either glucose or fructose solutions. Interestingly, the amount ingested, fractional turnover of stable carbon isotope signatures, amount oxidized, energy expended and proportion of hovering metabolism supported by each hexose, were each similar between glucose and fructose. These results demonstrate hovering hummingbirds’ ability to utilize fructose and glucose equally.

Abstract :The main goal of this stud y was to quantify the effect s of landscape structure on the abundance of Ruby-throate d Hummingbird s (Archilochus colubris) in forest patches and this, while accounting for its indirect effects on open flower community an d the occurrence of Yellow-bellied Sapsucker s (Sphympicus varius), a potential commensal of hummingbirds. We sampled 40 forest patches (0. 5 to >10 0 ha ) where we had installed 2 nectar feeders (forest edge and 40 m within forest ) during 2 breeding season s (2006 and 2007) . We visited forest patches weekly and recorded the number of hummingbirds detected within 10 m of feeders during 10 min. Mean daily artificial nectar consumption by hummingbirds, as well as their relative total abundance an d the respective relative abundance of adult males and females, were all affected by forest cover. Except for the relative total abundance, this effect of forest cover depended upon the size of forest patches. Nectar consumption and abundance generally peaked in forest patches of intermediate size found in landscapes characterized by intermediate forest cover. Mea n daily artificial nectar consumption and the relative total abundance, a s well as that of males, were higher at feeders located on the forest edge compared to 40 m inside forest patches. Regarding indirect landscape effects, landscape structure influenced the structure of open flower communities surrounding feeders, which in turn, affected the relative total abundance of hummingbirds, a s well as that of adult males. On the other hand, we failed to find strong evidence that landscape structure affected the occurrence of Yellow-bellied Sapsuckers or that the latter influenced Ruby-throated Hummingbird abundance patterns. These results support the idea that landscape structure may affect the abundance pattern of a species directly as well as through mechanisms which are themselves dependent upon the composition and configuration of landscapes //Résumé : La structure des paysages peut influencer l'écologie d'une espèce directement, en contraignant ses mouvements, par exemple, de même qu'indirectement en affectant, entre autres, l'abondance de ses proies ou prédateurs. Quoique plusieurs études aient tenté de quantifier l'influence de la structure du paysage sur les patrons d'abondance, rares sont celles qui ont mesuré simultanément les effets directs et indirects du paysage. L'objectif de ce mémoire consiste à modéliser simultanément les effets directs de la structure du paysage sur l'abondance relative du Colibri à gorge rubis ( Archilochus colubris ) et sa consommation de nectar artificiel ainsi que les effets indirects par lesquels le paysage peut aussi agir tels la disponibilité en ressources alimentaires (communautés floristiques) et la relation interspécifique de commensalisme avec le Pic maculé ( Sphyrapicus varius ). Pour ce faire, j'ai échantillonné 40 îlots forestiers (0,5 à >100 ha) dans la région de l'Estrie (Québec, Canada). À chacun d'eux, j'ai installé deux abreuvoirs (en bordure et 40 m à l'intérieur) durant les étés 2006 et 2007 et ont été visités de façon hebdomadaire. J'ai détecté une relation quadratique du couvert forestier dans le paysage avec l'abondance totale relative, celle des mâles et des femelles ainsi que pour la consommation quotidienne moyenne. Ces effets varient en fonction de la taille d'îlot sauf pour l'abondance relative totale. Les valeurs maximales se situent à des niveaux intermédiaires de couvert forestier et de taille d'îlots. Certaines caractéristiques mesurées étaient à l'échelle locale comme la position de l'abreuvoir dans l'îlot forestier ou la structure de la végétation. J'ai détecté un effet de bordure pour toutes les variables sauf l'abondance des femelles. L'indice de structure de végétation n'avait d'influence que sur l'abondance des mâles. Concernant les effets indirects, l'ensemble des variables du paysage explique 69,61% de l'indice de communauté floristique et ce dernier a un effet significatif sur l'abondance totale et l'abondance des colibris mâles. Pour la relation avec le pic, les variables du paysage mesurées n'ont pas permis de détecter un effet. De plus, bien qu'étant une variable non significative, les modèles incluant la présence du Pic maculé étaient généralement parmi les plus performants. L'ensemble de ces résultats soutient l'importance de combiner l'écologie du paysage et l'écologie comportementale dans les mêmes modèles afin de tenir compte non seulement des effets directs mais aussi des effets indirects du paysage //