Can ancient insect exoskeleton delta C-13 values be used to infer past vegetation types?

摘要

Insects encode proxy environmental information about regional vegetation structure in the stable carbon isotope (delta C-13) composition of their tissues. However, uncertainty lies in the exact relationship between "community" insect delta C-13 values and the overall structure of the vegetation from which the insects come, specifically the cover of C-3 and C-4 plants. This study aimed to determine this relationship using modern samples of insects collected from sites ranging from rain forest (high C-3 cover) to savanna (high C-4 cover) across an environmental gradient in tropical Australia. Insect delta C-13 values were strongly related to modern variations in C-3 and C-4 cover, although difficulties arose when estimating the vegetation structure of sites with low vegetation cover in arid central Australia. We further found the best models for predicting vegetation structure also included additional constraints provided by variation in precipitation. Overall, our results confirm that ancient insect delta C-13 values, such as those recovered from insectivorous bat and bird guano deposits, can indeed provide a robust palaeoenvironmental proxy for inferring the trajectory of past vegetation change in the tropics.