Temperature-dependent consumption of spiders by little brown bats (Myotis lucifugus), but not northern long-eared bats (Myotis septentrionalis), in northern Canada

Intraspecific variation in diet has been observed in many species, including the geographically widespread little brown bat (Myotis lucifugus (Le Conte, 1831)). Spider consumption by M. lucifugus is more common in northern regions of their distribution, possibly due to reduced availability of aerial prey during low temperatures. However, in previously studied northern regions, M. lucifugus was the only bat species captured. The purpose of our study was to examine whether there is overlap in the diet and morphology of M. lucifugus and the northern long-eared bat (Myotis septentrionalis (Trouessart, 1897)), a species that commonly gleans prey, in the Northwest Territories, Canada. There were significant differences in the dietary composition and wing morphology of the two species, suggesting partitioning of resources. Both species consumed spiders, although unlike M. septentrionalis, the probability of M. lucifugus consuming spiders was significantly greater at low temperatures. Myotis lucifugus demonstrated a different pattern of spider consumption than in other northern regions where it consumes spiders throughout the summer, suggesting the possibility of resource competition where M. lucifugus overlaps with M. septentrionalis. Further research is needed to determine whether arthropods are seasonally limiting at high latitudes and to examine how these species capture nonaerial prey, including spiders. Key words: diet, little brown bat, Myotis lucifugus, Myotis septentrionalis, northern long-eared bat, spiders, wing morphology. Des variations intraspecifiques du regime alimentaire ont ete observees chez de nombreuses especes, y compris le vespertilion brun (Myotis lucifugus (Le Conte, 1831)), une espece de vaste repartition geographique. La consommation d'araignees par M. lucifugus est plus repandue dans les regions nordiques de son aire de repartition, possiblement en raison de la moindre disponibilite de proies aeriennes quand les temperatures sont plus faibles. Dans les regions nordiques etudiees par le passee, M. lucifugus etait toutefois la seule espece de chauve-souris capturee. Le but de l'etude etait de verifier si les regimes alimentaires et les morphologies de M. lucifugus et du vespertilion nordique (Myotis septentrionalis (Trouessart, 1897)), une espece qui glane habituellement ses proies, se chevauchent dans les Territoires-du-Nord-Ouest (Canada). Des differences significatives ont ete observees sur le plan de la composition du regime alimentaire et de la morphologie des ailes entre les deux especes, ce qui indiquerait un partage differentiel des ressources. Les deux especes consomment des araignees, bien que, contrairement a M. septentrionalis, la probabilite que M. lucifugus consomme des araignees est significativement accrue a faible temperature. Myotis lucifugus presentait des habitudes differentes de consommation d'araignees que dans d'autres regions nordiques ou il consomme des araignees durant tout l'ete, ce qui evoque la possibilite d'une concurrence pour les ressources la ou les aires de M. lucifugus et M. septentrionalis se chevauchent. D'autres travaux sont necessaires pour determiner si les arthropodes posent des limites saisonnieres a hautes latitudes et pour examiner comment ces especes de chauves-souris capturent des proies non aeriennes, dont des araignees. [Traduit par la Redaction] Mots-cles : regime alimentaire, vespertilion brun, Myotis lucifugus, Myotis septentrionalis, vespertilion nordique, araignees, morphologie des ailes.
Introduction Species that have widespread geographic distributions are exposed to different environmental conditions across populations (Mayr 1963; Freckleton et al. 2003). Intraspecific variation and local adaptation within wide-ranging species have [...]