A simple, integrative assay to quantify nutritional quality of browses for herbivores
Date
2008
Authors
De Gabriel, Jane
Wallis, Ian
Moore, Ben
Foley, William
Journal Title
Journal ISSN
Volume Title
Publisher
Springer
Abstract
Many regard the concentrations of nitrogen (N), tannins and plant cell wall constituents (fibre) as key indicators of food quality and habitat suitability for browsing herbivores; yet there is no method for measuring their combined effects. We have developed a simple in vitro assay for measuring the effects of tannins and fibre on N availability in browse. We determined the effects of tannins by measuring the polyethylene glycol (PEG)-binding capacity (PEG-BC) of Eucalyptus leaf samples, followed by a two-stage in vitro digestion with pepsin and cellulase to determine the digestibility of dry matter and N. There was a significant relationship between concentrations of digestible N and the PEG-BC of the leaves. Furthermore, adding PEG significantly improved the digestibility of N. Our results concur with in vivo observations from several mammalian species. This suggests that our method is effective for measuring the nutritional quality of browse and the benefits of adding PEG, providing some index of the detrimental effects of tannins. We further simplified the assay by removing the PEG step, allowing us to quickly analyse samples in bulk. Nevertheless, this simplified method is still not practical for analysing the many samples necessary to compare the nutritional values of different tracts of forest. We used near-infrared reflectance spectroscopy to produce calibration equations and predicted total and digestible N in 322 trees at eleven sites. Both within and between sites, we found a wide variation in concentrations of digestible N but a much lower variation in total N, with either no relationship or poor relationships between the two measures. This confirms the variability in the nutritional quality of eucalypt forests, which may explain the distribution and abundance of mammalian herbivores. Thus, our assay provides a useful tool for understanding how food resources influence herbivore populations at different scales.
Description
Keywords
Keywords: macrogol derivative; nitrogen; tannin derivative; bioassay; browsing; evergreen forest; habitat quality; herbivore; infrared spectroscopy; mammal; nutrient availability; nutritive value; spatial distribution; article; chemistry; Eucalyptus; metabolism; ne Eucalyptus; Folivory; Nitrogen availability; PEG; Tannins
Citation
Collections
Source
Oecologia
Type
Journal article
Book Title
Entity type
Access Statement
License Rights
Restricted until
2037-12-31