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First published online April 8, 2004
Journal of Experimental Biology 207, 1741-1748 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00929

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Nitrogen stress causes unpredictable enrichments of ¹⁵N in two nectar-feeding bat species

Christian C. Voigt^1,* and Felix Matt²

¹ Institute for Zoo and Wildlife Research, Evolutionary Ecology Research Group, Postfach 601103, 10252 Berlin, Germany
² Institute of Zoology II, University Erlangen-Nürnberg, Staudtstr. 5, 91058 Erlangen, Germany

View larger version (13K): [in a new window]   Fig. 1. Nitrogen isotope ratios (15N; ) of the two diets and in wing membrane and blood of Leptonycteris curasoae (A) and Glossophaga soricina (B) equilibrated to diet 1. Data are given as box plots with the border of the boxes representing the 25 and 75 percentiles, the T-mark the 10 and 90 percentiles and the outermost points the 5 and 95 percentiles. The thick line within the box indicates the mean, and the thin line indicates the median.

View larger version (16K): [in a new window]   Fig. 2. Mean changes in body mass (±1 S.D.) of Leptonycteris curasoae (solid circles) and Glossophaga soricina (open circles) during the experiment. Linear regressions were calculated over mean values for each species (solid lines). On average, both species lost 8% of their body mass during the experiment.

View larger version (32K): [in a new window]   Fig. 3. Changes in nitrogen isotope ratio (15N; ) in two tissues of Leptonycteris curasoae (A,C) and Glossophaga soricina (B,D) after the diet was changed at day one to plant products with a nitrogen isotope ratio that was more enriched in 15N by 9 15N than the initial diet; mean values (± 1 S.D.) for blood are shown in A and B (open circles) and those for wing membrane in C and D (filled circles). Exponential regression functions were fitted to the data sets (solid line; see equations in the corresponding graphs). Broken lines give the expected regression lines calculated with the corresponding regression coefficients derived from the carbon isotope data set (Voigt et al., 2003b).

View larger version (17K): [in a new window]   Fig. 4. Relationship between the estimated half-life of isotopes in blood (A,B) and wing membrane (C,D) (filled circles, nitrogen isotopes; open circles, carbon isotopes; data from Voigt et al., 2003b). The estimated half-life of nitrogen isotopes was not significantly correlated with body mass loss (Table 2). The sample volume was too small in some cases to measure the nitrogen isotope ratio. Thus, we could not calculate individual t50 values for these individuals (one data point in A and C; two data points in B and D).