Chemical parameters of decomposing dung in tropical forest as indicators of feeding behaviour of large herbivores: A step beyond classical stoichiometry

摘要

Feeding behavior of large herbivores determines the composition of their dung and together with environmental factors the intensity of decomposition processes leading to the recycling of nutrients in tropical forests. Large herbivore dung and its decomposition has so far been characterized by stoichiometric analyses of elements such as C and N. The objective of our study was to examine the suitability of biomarker analyses and analytical pyrolysis to infer large herbivore feeding behavior and the decomposition of their dung in different environments. Our conceptual approach included exposure of fresh dung of a grazing ruminant (gaur, Bos gaurus) and a non-ruminant mixed-feeder (the Asian elephant, Elephas maximus) in two tropical forest types (dry and moist) and analysis of dung biochemical composition in two seasons (dry and wet). To this end we characterized the dungs' lignin and carbohydrate (sugar) signatures and pyrolysis products before and after 28 days of exposure.Our results showed that stoichiometric as well as biomarker analyses were able to differentiate gaur and elephant dung independent of season and forest type, while analytical pyrolysis products did not differ between dung types. The lignin signature of fresh dung additionally indicated the forage preference of animals in different forest types and seasons. During decomposition, C and N contents decreased and the chemical composition of both dung types converged. The lignin signature of dung at the end of the experiment showed higher lignin decomposition in moist forest and wet season than dry forest and dry season. We conclude that detailed biochemical analyses can provide deeper insights into the main controls of large herbivore dung and its decomposition in tropical forests than stoichiometric analysis. In particular lignin may be a suitable indicator to investigate large herbivore feeding behavior and the environmental conditions of their habitat.