The utilisation of coprophilous fungal spores for discerning late Quaternary megaherbivore extinctions in Canada

Abstract

Northern ecosystems are experiencing dramatic changes due to anthropogenically accelerated climatic warming. Understanding the impacts of this on fauna and flora is key to predicting the long-term sustainability of northern environments. This requires long-term data sets of ecosystem response to environmental change from environments and climates contiguous to contemporary conditions. One event is the climatic warming recorded at the Pleistocene- Holocene transition that resulted in the extinction of 35 megafaunal genera and loss of the mammoth steppe biome in East Beringia. Previous studies have relied on spatially and temporally correlating bone remains, but coprophilous fungi preserved in lake sediments have recently been used as a complimentary proxy for reconstructing megaherbivore populations. A high-resolution record spanning this transition has been reconstructed using a sediment core collected from Gravel Lake, central Yukon Territory. Pollen and coprophilous fungi were complimented by radiocarbon-dated bone remains from Alaska and Yukon Territory. Results indicate the local extirpation of megaherbivores at the beginning of the Holocene (ca. 11,000 to 10,400 cal yr BP) by a decline in coprophilous fungi and a lack of bone remains from Yukon Territory. However, skeletal records indicate the loss of mammoths and horses at ca. 13,000 cal yr BP, 2000 years prior to the fungi records. At this time, pollen assemblages from Gravel Lake indicate the last environments contiguous with the mammoth steppe from this region. The data highlight a faunal turnover at ca. 13,000 cal yr BP with the proliferation of browsing taxa, but it is still unclear why only mammoth and horse populations are lost and not other grazing taxa such as bison and muskox. A secondary study analysed remains preserved in mastodon dung dated to the marine isotope stage 5a/4 transition of Nova Scotia. Results indicate a wetland rich in charophytes, sedges, cattails, bulrushes and bryophytes in a spruce-dominated boreal forest. The limited diversity and abundance of coprophilous fungi in the dung could be attributed to a browser feeding habit. If so, this could have a considerable impact on understanding the influence of feeding ecologies on the presence of coprophilous taxa in lake sediments, and thus inferences of megaherbivore abundance.