Lynch’s Crater

Long ago, a volcano collapsed, creating an 80 yard deep crater.  Lynch’s Crater, located in northeastern Australia, has since become half-filled with 230,000 years worth of lake and marsh sediment. This sedimentary deposit has preserved pollen evidence spanning 2 complete glacial/interglacial cycles.  From this evidence scientists know a wet rain forest prevailed in this region until man arrived here about 40,000 years ago.  The actions of Australian aborigines converted the rain forest to a dry woods dominated by fire-adapted trees such as eucalyptus.  This environmental change was not associated with any shift in glacial cycle.  Instead, man overhunted the megafauna into extinction and began setting frequent fires.  The large biomass of megaherbivores was no longer consuming vast amounts of vegetation, leaving lots of flammable material for men to burn.  Grazers and browsers were no longer suppressing plant growth, facilitating seed dispersal, and recycling nutrients in their dung.  Species of fungi, dependent upon megaherbivore dung for reproduction, declined in abundance.  Scientists use the measurable quantity of dung fungus spores in dated cores as a proxy for the former biomass of large herbivores.  Dung fungus is actually a  more reliable indicator of former megaherbivore presence than the fossil remains of these beasts because bones are rarely preserved.  Scientists have used this clue to study ancient megafaunal populations in North America, Europe, Madagascar, and Australia.  However, some researchers have noted some problems with using dung fungus spores as a proxy for megafaunal populations.  Chris Johnson, an Australian zoologist, along with other scientists, have addressed these concerns by implementing solutions in a study of data collected from Lynch’s Crater.

Location of Lynch’s Crater.  Sediment within the crater provide a 230,000 pollen record, illustrating how plant and animal communities changed over time.

 

Lynch's Crater (facing south)

Photo of Lynch’s Crater.  For over 100,000 years it was a lake but over the past 50,000 years it has been a marsh.

Some researchers have noted that dung fungus spores disperse over short distances, and their abundance can be effected by drought.  This can cause a variability in spore abundance unrelated to the abundance of megeherbivores.  Another problem is the variation in the amount of pollen produced by plants.  Because dung fungus is numerically expressed as a value relative to pollen counts, it can be difficult to compare fungus proxy values between studies.  Dr. Johnson and his colleagues executed 3 solutions to these problems.

1. They took core samples from different locations within the study area to minimize local effects.

2. They expressed dung fungus abundance independently from pollen counts.  They found interpretations of spore counts when expressed as a percent of pollen were not influenced by changes in vegetation type.

3. They compared trends in the quantity of dung fungus spores with spores from fungi that don’t rely on megaherbivore dung for reproduction.

Sordaria

 

 

 

 

Sordaria humana.  This species of dung fungus prefers human and dog shit.  While other species of dung fungus declined in abundance following the extinction of the megafauna, the abundance of this species remained strong and even increased after humans colonized Australia.

This study counted the volume of spores from 5 genera of fungi extracted from dated cores.  Sporormiella and podospora depend upon megaherbivore dung for reproduction.  Sordaria, coniochaeta, and cerophora spores occasionally land on megaherbivore dung, but these are generalist genera not as dependent upon megaherbivore dung for reproduction. There was a significant difference in decline between fungi dependent upon megaherbivore dung and generalist fungi.  Sordaria humana is a species of fungus that reproduces readily on human and dog feces.  Sordaria spores remained steady in abundance after 40,000 BP when sporormiella and podospora declined.

This study found that the volume of dung fungus spores in Australia prior to 40,000 BP was similar to numbers from studies conducted of Pleistocene North America, Pleistocene Europe, late Holocene Madagascar, and modern livestock producing regions.  This suggests the biomass of megaherbivores in pristine environments was close to what modern pastures can support.  Data from this study also show the extinction of Australia’s megafauna is closely associated with the initial presence of man.  It appears as if man hunted these animals into extinction within a 1000 year time span.  The transformation of wet tropical forest to dry fire-adapted woods occurred after the megafauna became extinct, precluding the possibility that climate change was a factor in the extinction of Australia’s megafauna.

Reference:

Johnson, Chris; et. al.

“Using Dung Fungi to Interpret Decline and Extinction of Megaherbivores: problems and solutions”

Quaternary Science Reviews Feb 2015

 

 

 

 

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