Fecal proxies

By Dulcinea Groff

Dung fungus spores of Sporormiella australis. From Funghi Paradise.

Dung fungus spores of Sporormiella australis. From Funghi Paradise.

Feces of prehistoric organisms remaining in the sediment records harbor information that can lead to a picturesque reconstruction of an ecosystem from long ago.  It is quite remarkable how many examples of fecal proxies exist and provide more information than just an indication of the presence or absence of an animal.  In the early 1800’s, an eccentric paleontologist named William Buckland was the first to describe coprolites or fossilized feces.  When feces become fossilized the organic components are replaced with minerals and any clue as to what the organism ate is replaced.  Therefore, coprolites may not be very useful in understanding the ecology of past environments and organisms.  Instead, other things associated with feces become proxies in paleoecological studies. Continue reading

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Attaching dates to lake sediment cores: precise dating using varves

By: Rob Brown

There are many proxies paleoecologists use to determine past environments and communities (insects, pollen, diatoms, packrat middens, tree rings, etc.), many of which have been discussed on this blog previously. These proxies can be used to answer questions ranging from seasonal to millennial time scales. With the exception of tree rings, which were previously discussed on this post by Erin our reconstructions are often limited by errors in dating methods. However in some lakes, sediments are deposited in visible annual layers called varves. Varved sediments offer a unique situation where the temporal resolution necessary to determine annual to decadal changes relevant to a human lifetime can be achieved.

Figure 1. Varve sediment from Newbury, Vermont, USA. Note the alternating light and dark bands and different thicknesses. From Tufts University North American Glacial Varve Project

Figure 1. Varve sediment from Newbury, Vermont, USA. Note the alternating light and dark bands and different thicknesses. From Tufts University North American Glacial Varve Project

What are varves and where are they found?

Simply put, a varve is an annual layer of sediment that forms in distinct layers (Figure 1). A single year’s deposit includes a light (summer) layer and a dark (winter) layer.

Varves don’t form in all lakes, in fact they are found in very few. The main factor controlling varve formation is climate variability; there must be large seasonal differences in both temperature and precipitation. This sets up the succession of biotic life and the physical and chemical structure of the lake necessary to form the contrasting layers. Additionally, there needs to be no disturbance of the sediment once it is deposited. Processes such as underwater currents, sediment slumping (think underwater mudslides), degassing (air bubbles within the sediment), or bioturbation (organisms physically mixing the sediment) all mix the sediment layers and the annual deposits are lost (O’Sullivan, 1983). Continue reading

Small but Mighty: Insects as Proxies

By Wayne Heideman

Insects have been on the Earth for a long time and their presence can affect their surrounding environment. It is important to look at insects in the past as they can provide us with insight on how they can act in the present and in the future. In a paleoecological sense, insects can be studied in a number of ways. One way is to look at plant-insect interactions through plant fossils (herbivory) and peatlands (habitat). Another technique is through amber and observing the insect in a snapshot of time. Lastly, sediment cores in lakes can capture insect presence, notably Chironomidae (non-biting midges) larvae and Coleoptera (beetles). All three are viable means of observing past insect use but they all have their strengths and weaknesses which should be assessed before using a specific method.

A picture of three different types of insect damage on plants. A) Shows a frass trail as well as an oviposition site marked by the arrow. B) Shows a high degree of herbivory, only leaving fine veins and C) shows areas of leaf case shelter sites. From Wilf 2008.

A picture of three different types of insect damage on plants. A) Shows a frass trail as well as an oviposition site marked by the arrow. B) Shows a high degree of herbivory, only leaving fine veins and C) shows areas of leaf case shelter sites. From Wilf 2008.

Continue reading