The carbon isotope biogeochemistry of the individual hydrocarbons in bat guano and the ecology of the insectivorous bats in the region of Carlsbad,New Mexico |
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| Authors: | David J Des Marais JM Mitchell WG Meinschein JM Hayes |
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| Institution: | Ames Research Center, NASA, Moffett Field, CA 94035 U.S.A.;Department of Geology, Indiana University, Bloomington, IN 47405, U.S.A. |
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| Abstract: | The structures and 13C contents of individual alkanes extracted from bat guano found in the Carlsbad region of New Mexico can be related to both the photosynthetic pathways of the local plants and the feeding habits of the insects that support the bats.Carbon isotopic analyses show that equivalent numbers of C3 and C4 native plant species occupy the Pecos River Valley, a very significant feeding area for the Carlsbad bats. During the seasons when bats frequent the area, the agricultural crops consist principally of alfalfa and cotton, both C3 plants.The molecular composition of the bat guano hydrocarbons is fully consistent with an insect origin. Two isotopically distinct groups of insect branched alkanes were discerned. These two groups of alkanes derived from two chemotaxonomically distinct populations of insects possessing distinctly different feeding habits. It is possible that one population grazes predominantly on crops whereas the other population prefers native vegetation. This and other isotopic evidence suggests that crop pests constitute a major percentage of the bats' diet.Because the guano sample was less than 40 years old, this material reflects the present day plant community in the Pecos River Valley. Future studies of more ancient guano deposits should reveal a measurable influence of both natural and man-induced vegetative changes with time upon the 13C content of the bat guano hydrocarbons. |
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