Advantages of using fecal samples for stable isotope analysis in bats: evidence from a triple isotopic experiment.
BACKGROUND
Stable isotope analysis in ecological studies is usually conducted on biomaterials, e.g. muscle and blood, that require catching the animals. Feces are rarely used for stable isotope analysis, despite the possibility of non-invasive sampling and short-term responsiveness to dietary changes. This promising method is neglected due to a lack of calibration experiments and unknown diet-feces isotopic difference (Δ(diet-feces)).


METHODS
To fill this gap, we simulated trophic changes occurring in nature when animals switch feeding habitats, e.g. by moving from freshwater to terrestrial systems, from cultivated areas to forests or changing distance from marine environments. In a controlled experiment, the diet of two bat species (Myotis myotis, Rhinolophus ferrumequinum) was altered to an isotopically distinct one. We measured stable nitrogen, carbon and the rarely used sulfur isotope in feces, and calculated Δ(diet-feces) values.


RESULTS
The feces acquired the new dietary signature within 2-3 h from food ingestion; thus, they are suited for detecting recent and rapid dietary changes. The Δ(diet-feces) (Δ) did not differ between species or diet (overall means ± standard deviation (sd)): Δ(15)N: 1.47 ± 1.51‰, Δ(13)C: -0.11 ± 0.80‰, Δ(34)S: 0.74 ± 1.10‰. Only Δ(15)N for M. myotis was significantly different from zero and only Δ(13) C differed among the days of the experiment.


CONCLUSIONS
Fecal stable isotopes can be now further applied in mammalian ecology. This includes a range of applications, such as studying changes in trophic level, resource or habitat use, on a short time-scale. Such information is gaining importance for monitoring rapidly changing ecosystems under anthropogenic influence.
Limnological Institute, University of Konstanz, Mainaustrasse 252, D-78464 Konstanz, Germany. Ioanna.Salvarina@uni-konstanz.de
Ioanna
I
Salvarina
Elizabeth
E
Yohannes
Björn M
BM
Siemers
Klemen
K
Koselj
D000821:Animal Feed / Q000032:analysis; D000818:Animals; D002247:Carbon Isotopes / Q000032:analysis* / Q000378:metabolism; D002685:Chiroptera / Q000378:metabolism*; D017753:Ecosystem; D005243:Feces / Q000737:chemistry*; D009587:Nitrogen Isotopes / Q000032:analysis / Q000378:metabolism; D013460:Sulfur Isotopes / Q000032:analysis / Q000378:metabolism
D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D013460:Sulfur Isotopes