title: Field metabolic rates of phytophagous bats: do pollination strategies of plants make life of nectar-feeders spin faster?
abstract: Recently, it was argued that extrinsic factors, such as high foraging costs, lead to elevated field metabolic rates (FMR). We tested this suggestion by comparing the FMR of nectar-feeding and fruit-eating bats. We hypothesized that the foraging effort per energy reward is higher for nectar-feeding mammals than for fruit-eating mammals, since energy rewards at flowering plants are smaller than those at fruiting plants. Using the doubly labelled water method, we measured the FMR of nectar-feeding Glossophaga commissarisi and fruit-eating Carollia brevicauda, which coexisted in the same rainforest habitat and shared the same daytime roosts. Mass-specific FMR of G. commissarisi exceeded that of C. brevicauda by a factor of almost two: 5.3+/-0.6 kJ g(-1) day(-1) for G. commissarisi and 2.8+/-0.4 kJ g(-1) day(-1) for C. brevicauda. Since nectar-feeding bats imbibe nectar droplets of only 193 J energy content during each flower visit, a G. commissarisi bat has to perform several 100 flower visits per night to meet its energy requirement. The fruit-eating C. brevicauda, on the other hand, needs to harvest only 3-12 Piper infructescenses per night, as the energy reward per Piper equals ca. 6-30 kJ. We argue that the flowering and fruiting plants exert different selective forces on the foraging behaviour and energetics of pollinators and the seed dispersers, respectively. A comparison between nectar-feeding and non-nectar-feeding species in various vertebrate taxa demonstrates that pollinators have elevated FMRs.
authors.affiliation: Institute for Zoo and Wildlife Research, Evolutionary Ecology Research Group, PF 601103, 10252 Berlin, Germany. voigt@izw-berlin.de
authors.forename: Christian C
authors.initials: CC
authors.lastname: Voigt
authors.forename: Detlev H
authors.initials: DH
authors.lastname: Kelm
authors.forename: G Henk
authors.initials: GH
authors.lastname: Visser
mesh_terms: D000818:Animals; D001835:Body Weight; D002685:Chiroptera / Q000378:metabolism*; D017753:Ecosystem; D002149:Energy Intake; D004734:Energy Metabolism / Q000502:physiology*; D005247:Feeding Behavior / Q000502:physiology*; D005518:Food Preferences; D005638:Fruit; D011058:Pollen / Q000502:physiology*; D013045:Species Specificity; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water