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The stable isotopic compositions of nitrogen and carbon in animal tissues reflect diet. However, factors other than diet can also affect these stable isotope ratios, leading to misinterpretations of diet composition. To test the hypothesis that variation in metabolic rate alters the isotopic compositions of tissues, deer mice (Peromyscus maniculatus (Wagner, 1845)) were kept at three temperatures (thermoneutral (23°C), cool (5°C), and cold (-10°C)) and fed ad libitum. The changes in carbon and nitrogen isotope compositions of liver associated with the thermoneutral versus cool and cold conditions were very small in comparison with those arising from differences in diet. We conclude that temperature-induced variations in metabolic rate are insufficient to produce differences in the stable carbon or nitrogen isotope compositions that could be mistaken for changes in diet. Les compositions d'isotopes stables d'azote et de carbone dans les tissus animaux refletent le regime alimentaire. Cependant, des facteurs autres que le regime peuvent affecter ces rapports d'isotopes stables, ce qui entraine des interpretations erronees de la composition du regime alimentaire. Afin de tester l'hypothese qui veut que la variation du taux metabolique affecte la composition isotopique des tissus, nous avons garde des souris du crepuscule (Peromyscus maniculatus (Wagner, 1845)) a trois temperatures differentes, soit des regimes thermiques neutre (23°C), frais (5°C) et froid (-10°C), et les avons nourries a volonte. Les modifications dans les compositions d'isotopes de carbone et d'azote dans le foie associees au regime thermique neutre par rapport a ceux des regimes frais et froids sont tres petites par comparaison a celles qui proviennent de differences de regime alimentaire. Nous en concluons que les variations du taux metabolique causees par la temperature ne sont pas assez importantes pour produire des differences de composition des isotopes stables de carbone et d'azote qui pourraient etre interpretees par erreur comme des changements de regime alimentaire. [Traduit par la Redaction], Introduction Measurement of stable carbon ([sup.13]C/[sup.12]C) and nitrogen ([sup.15]N/[sup.14]N) isotope ratios is commonly undertaken in ecological studies because the compositions of tissues reflect the composition of the diet (Kelly 2000). [...]

Berry crops in the southwestern Yukon were quantified from 1997 to 2008 at 10 locations along 210 km of the Alaska and Haines highways. We tested the hypothesis that the size of berry crops could be predicted from spring and summer temperature and rainfall of years t, t-1 (1 year prior), and t-2 (2 years prior). Six common species were studied in the boreal forest of the Kluane region: Arctostaphylos rubra (Rehd. & Wils.) Fern., Arctostaphylos uva-ursi (L.) Spreng. s.l., Empetrum nigrum L., Vaccinium vitis-idaea L., Geocaulon lividum (Richards) Fern, and Shepherdia canadensis (L.) Nutt.. For the first five species we counted berries on fixed 40 cm x 40 cm quadrats to obtain an index of berry production for the Kluane region for each of the 12 years, and for S. canadensis we counted berries on two tagged branches of 10 bushes at each location. Stepwise multiple regressions were utilized to predict the size of berry crops for each species. For all species, predictive equations could explain statistically 80%-96% of the variation in berry crops. Different weather variables characterized each plant species, and there was no common weather regression that could explain the variation in berry crops in all species. Rainfall and temperature from years t-1 and t-2 were typically the significant predictors. There was no indication of a periodicity in berry production, and 43%-60% of the quadrats counted had large berry crops at one year intervals, while other quadrats never had a high crop during the study interval. Key words: berry production, Yukon, climate, Kluane, dwarf shrubs. Les auteurs ont quantifie les recoltes de baies dans le sud-ouest du Yukon de 1997 a 2008, a 10 endroits sur 210 km le long des autoroutes d'Alaska et de Haines. Its ont verifie l'hypothese qu'on pourrait predire l'importance des recoltes de petits fruits a partir des temperatures estivales des annees t, t-1 et t-2. Its ont etudie six especes communes de la foret boreale dans la region de Kluane: Arctostaphylos rubra (Rehd. & Wils.) Fern., Arctostaphylos uva-ursi (L.) Spreng. s.l., Empetrum nigrum L., Vaccinium vitis-idaea L., Geocaulon lividum (Richards) Fern et Shepherdia canadensis (L.) Nutt. Chez les 5 premieres especes, on a compte les baies sur des quadrats fixes de 40 cm x 40 cm afin d'obtenir un index de la production des baies dans la region de Kluane pour chacune des 12 annees, et pour le S. canadensis on a compte les baies sur deux branches marquees chez 10 bosquets sur chaque site. Les auteurs ont utilise la regression multiple progressive pour predire la dimension des recoltes de petits fruits pour chaque espece. Chez toutes les especes, les equations predictives peuvent expliquer statistiquement 80-96 % de la variation des recoltes de petits fruits. Differentes variables climatiques caracterisent chaque espece de plante, et on n'observe pas de regression commune qui pent expliquer la variation des recoltes de baies chez toutes les especes. La precipitation et la temperature des annees t-1 et t-2 constituent des pronostiques significatifs. Il n'y a pas d'indication qu'il existerait une periodicity dans la production des baies, et 43-60 % des quadrats enumeres montrent de fortes productions de baies a un an d'intervalles, alors que les autres quadrats n'ont jam ais montre de fortes recoltes tout an long de l'etude. Mots-cles : production de baies, Yukon, climat, Kluane, arbustes nains. [Traduit par la Redaction], Introduction Berry crops in the boreal forest region vary dramatically from year to year. A combination of soil factors and climatic events are usually put forward to explain these variations [...]

Epigeous mushroom production in the boreal forest ecosystem varies dramatically from year to year. We tested the hypothesis that the aboveground production of epigeous mushrooms in the Kluane region, Yukon, could be predicted by summer rainfall. There is a single crop in this part of the boreal zone with maximum production during the first 2 weeks of August. We measured standing crops from 1993 to 2007 at 13 areas along 210 km of the Alaska Highway and Haines Road in the southwestern Yukon. Aboveground mushroom crops averaged 24 kg/ha wet weight but varied from 0.0 to 117 kg/ha over the 15 years of study, with a coefficient of variation among years of 143%. Epigeous mushroom production could be predicted from June rainfall of the current year and May rainfall of the year previous with [R.sup.2] = 0.85. Part of the lack of a perfect fit to rainfall was due to the constraint that years of high mushroom crops could not be followed by another high year, no matter what the rainfall pattern. We were not able to identify the species of mushrooms in this study but we confirm from natural history observations that mushrooms are a critical food for several of the small mammal species in the Yukon boreal forest. Key words: epigeous mushrooms, biomass prediction, boreal forest, Kluane Lake, Yukon, rainfall. La production de champignons epiges des ecosystemes de la foret boreale varie fortement d'une annee a l'autre. Les auteurs ont verifie l'hypothese a savoir que la production, au-dessus du sol, des champignons epiges dans la region de Kluane au Yukon, pourrait etre predite a l'aide de la precipitation estivale. Dans cette partie de la foret boreale, il y a une seule poussee avec un maximum de production au cours des deux premieres semaines d'aout. Ils ont mesure la ressource produite annuellement de 1993 a 2007 sur 13 sites etales sur 210 km de l'autoroute de l'Alaska et de la route Haines, dans le sud-ouest du Yukon. La productivite epigee en champignons atteint une moyenne de 24 kg/ha en poids frais, mais a varie de 0,0 a 117 kg/ha au cours des 15 annees de l'etude, avec un coefficient de variation au cours des annees de 143 %. On peut predire la production des champignons epiges a partir de la precipitation en juin de l'annee en cours et celle de mai de l'annee precedente avec [R.sup.2] = 0,85. On constate que les annees de fortes productions de champignons ne peuvent pas etre suivies par une autre annee de forte production, quel que soit le patron de precipitation; ceci constitue une contrainte qui empeche d'obtenir une correlation parfaite. Les auteurs n'ont pas ete en mesure d'identifier les especes de champignons dans cette etude, mais les observations de naturaliste confirment que les champignons y constituent une nourriture critique pour plusieurs des petits mammiferes qui vivent dans la foret boreale du Yukon. Mots-cles : champignons epiges, prediction de la biomasse, foret boreale, lac Kluane, Yukon, pluie. [Traduit par la Redaction], Introduction Aboveground mushroom crops in the boreal forest are known to fluctuate dramatically from year to year, and these crops are used as food both by small mammals and the [...]

Abstract: The hormonal stress response is adapted to deal with acute (short-term) stressors; however, chronic (long-term) stressors have negative effects on survival and fitness. Field and laboratory evidence suggest that [...]

Biological invasions erode ecosystem functioning and occur more frequently in freshwater ecosystems than in terrestrial environments. Nonphysical deterrents may be used to limit invasive fish dispersal, without altering the streamflow or connectivity of a watershed. Little is currently known about how behavioral variation among individuals may affect the efficacy of a deterrent, although such variation has been shown to affect fish dispersal in other contexts, such as range expansion. Furthermore, deterrent effectiveness is rarely tested when fish are motivated to disperse. Across a control, CO2, and CO2 + deterrent treatment, we quantified the avoidance response of invasive Common Carp Cyprinus carpio to a combined acoustic‐stroboscopic deterrent. In the CO2 treatment, we motivated individuals to enter a novel environment by degrading the home chamber of a choice arena with a continuous infusion of CO2. In the CO2 + deterrent treatment we introduced acoustic and stroboscopic stimuli to delay the departure of the fish and evaluate the efficacy of the deterrent. Finally, we tested a subset of the fish multiple times to determine whether they consistently responded to the same concentration of CO2. We found that the acoustic and stroboscopic deterrent could detain the fish in an increasingly unfavorable environment. Common Carp took only 195 and 131 s, respectively, to swim between the chambers during the control and CO2 treatment but took an average of 596 s in the CO2 + deterrent treatment. High CO2 concentrations in the CO2 + deterrent treatment led to most fish eventually dispersing toward the deterrent stimuli. Avoidance behavior varied widely within the CO2 + deterrent treatment, and Common Carp expressed repeatable differences in the tank‐inflow CO2 concentrations that were observed during chamber departure. Such interindividual variation in deterrent avoidance indicates that some individuals within a given species are more likely to move past a deterrent than others. [ABSTRACT FROM AUTHOR]

We examined growth, immune response, and basal corticosterone (CORT) levels in tree swallow (Tachycineta bicolor) nestlings over two years (2004 and 2005), and at two sites differing historically in insect abundance. We adjusted all broods to a common size of 6 nestlings. To assess the cell-mediated immune response, we injected phytohaemagglutinin (PHA) into the wing webs of two nestling per nest, followed by measurement of the swelling response 24 hours later. Humoral immune response was studied by vaccinating two nestlings per nest with either sheep red blood cells (SRBC; 2004), or with Newcastle Disease Virus (NDV; 2005). Blood samples were collected 7 days later to measure either anti-SRBC or anti-NDV titres. The remaining two nestlings per nest were blood sampled for determination of basal CORT levels. Nestling growth rates were significantly higher at the breeding site with historically higher insect abundance. Nonetheless, neither CORT levels nor the PHA swelling response differed between the two breeding sites, suggesting little evidence of a trade-off between growth rates and cell-mediated immunity. No antibodies to either SRBCs or NDV were detected in plasma of nestlings, likely as a result of their immature immune system. We suggest that natural variation in insect abundance has minimal effects on cell-mediated or humoral immunity in tree swallow nestlings.