Saturday, 5 January 2013

The Pro’s and Cons of the Sporormiella Proxy

 Sporormiella  spores used as a proxy to determine megafaunal existence

It has been argued that Sporormiella proxy can be used as a measure of large herbivore presence and abundance (Robinson et al 2005). In this blog I will explore the ideas of Feranec et al (2011), who looked at the advantages and disadvantages of using this proxy as an accurate dating method of extinct megafauna. An evaluation of this proxy might be useful in understanding whether it is a useful method of determining past megafauna during the Late Quaternary.

Proxies are widely employed in Quaternary paleoecology and the geosciences. When there is no direct method to establish organism presence, population size and other important demographics, proxies are used as a substitute (Feranec et al 2011). Sporormiella is a genus of fungi that is present on dung.  The spores are used as a proxy as they are preserved in lake sediments and easily identifiable due to being dark brown in colour and having a pronounced sigmoid germination pore.  Plant material and adhering spores are eaten by herbivores, and the spores pass through the digestive tract and are released as defecation. Spore abundance is related to the amount of dung present and has been an important tool in the analysis of extinct mammals in North America during the late Pleistocene.

Feranec et al (2011) identifies some of the problems with using Sporormiella as a proxy. Firstly, the fungus can be abundant on dung of the extant non-livestock megafauna and modern small mammals (Graf & Chmura 2006). This is problematic as it may weaken the accuracy of results looking at just solely megafauna. Secondly, a decrease in Sporormiella spore percentages does not necessarily mean a decline in megafaunal population size. Sporormiella is more abundant near lake shores than in the middle of lakes (Raper and Bush 2009), thus a decrease in this proxy could relate to an increase in lake level. Finally, Feranec et al (2011) raises concerns that the absence of Sporormiella does not necessarily mean an absence of large mammals from the local environment. An investigation carried out by Nyberg & Persson (2002) showed that habitat type had an effect in the abundance of fungi. This reinforces evidence to suggest that spore diversity is not necessarily related to megafunal presence or absence.

Therefore the issues associated with using Sporormiella as a proxy make it difficult to accurately determine megafaunal population presence, decline, and extinction during the late Pleistocene. To achieve robust interpretations about megafaunal extinctions and population collapse from Sporormiella counts, it is important to determine properties of the local vegetation and soil, as well as watershed characteristics and hydrodynamics of the study sites over time (Feranec et al 2011). Therefore it is important not to over rely on the accuracy of Sporormiella spores as other proxies provide better understanding for end-Pleistocene extinction. The use of Sporormiella should not be disregarded complexly as it is a potentially promising, and analysis in later years might become a more accurate method of dating. Using Sporormiella with other proxies would provide a most accurate and reliable technique of determining presence and abundance of megafauna as well as reasons behind population extinction.

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