Efficiency of facultative frugivory in the nectar-feeding bat Glossophaga commissarisi: the quality of fruits as an alternative food source |
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Authors: | Detlev H Kelm Juliane Schaer Sylvia Ortmann Gudrun Wibbelt John R Speakman Christian C Voigt |
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Institution: | (1) Leibniz Institute for Zoo and Wildlife Research, PF 601103, 10252 Berlin, Germany;(2) Department of Zoology, Humboldt University, Berlin, Germany;(3) School of Biological Sciences, University of Aberdeen, Aberdeen, Scotland, UK |
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Abstract: | The efficiency of food exploitation correlates positively with the extent of dietary specialization. Neotropical nectar-feeding
bats (Glossophaginae) have one of the most specialized diets among mammals, as floral nectar constitutes a sugar-rich and
highly digestible but protein and fiber depleted food source. However, dietary constraints, such as a temporary scarcity of
nectar, or protein demands may sometimes require the uptake of alternative food items. We investigated the influence of a
diet switch from nectar to fruit on intestinal morphology, body mass, and energy budget in the nectar-feeding bat Glossophaga commissarisi and quantified feeding efficiency. We hypothesized that these nectar specialists depend on a constant supply of nectar, if
they were lacking the ability for morphological and physiological plasticity in response to a fiber-rich diet. Although capable
of harvesting infructescences of Piper hispidum, G. commissarisi was less efficient in extracting energy from fruits (48% digestive efficiency of total fruit energy content) than from nectar
(c. 99% digestive efficiency). The intestinal morphology and organ masses did not change after bats were switched from nectar
to fruits. Captive bats exhibited lower daily energy expenditures and flight activity when feeding on fruits than during nectarivory.
Possibly, this may have been a deliberate regulation to balance reduced feeding efficiency, or simply the consequence of extended
digestive pauses. The low digestibility of Piper, in combination with slow digestion and the bats’ inability for morphological and physiological plasticity may cause nectar-feeders
to reduce their maximum energy expenditure when feeding on fruits. We argue that although fruits may substitute for nectar,
they may cause restricted maximum energy assimilation compared with nectar. |
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Keywords: | Glossophaga Digestive efficiency Frugivory Nectarivory Nutrient analysis |
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