Lecture 3 Palaeoecology PDF

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Simon Blockley...

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Lecture 3 Principles of Palaeoecology: -

Palaeoecology: The study of the relationships between ancient organisms and their environments Also defined as the “art/science of fleshing out an ancient ecosystem from bits and pieces of the fossil record It involves a combination of geology and biology/ecology

Philosophy of Palaeoecology: -

Inductive reasoning – observations, building up a series of observations about the past record – build up a picture The possibility of multiple working hypotheses – idea that there is just not one theory but multiple ideas Simplicity – Ockham’s razor (AD 1288-1348) – “It is vain to do with more what can be done with fewer” – concept that the simplest answer is usually the best one Taxonomy Data Uniformitarianism

The Principle of Uniformitarianism: -

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First suggested by James Hutton in AD 1788: “The result, therefore, of our present enquiry is, that we find no vestige of a beginning, -no prospect of an end” It was fully discussed by Charles Lyell in AD 1830 in “Principles of Geology” This principle states that the present is the key to the past – so that presently observable geological and biological processes are adequate to explain geological history.

Example: Salix herbacea -

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A species of the willow family Also called the least willow or snow bed willow Is one of the smallest woody plants in the world The map by Beerling (1998) shows the distribution of this plant in the British Isles – as shown it is most concentrated in high mountainous areas – therefore we could infer that this plant prefers colder conditions. The second image shows the distribution of the plant in Europe – as shows it’s distribution supports our observation that the plant thrives well in high altitude mountainous conditions Statements by Beerling (1998): o 1. “S. herbacea requires some degree of regular disturbance, e.g. exposure, snow cover, solifluction or grazing” o 2. “It has been argued that the geographical distribution of S. herbacea in the British Isles is closely delimited by… the maximum summer temperature” (23oC maximum summer temp). o 3. S. herbacea occurs in areas with minimum temperatures down to -20o – so can survive cold winters Past distribution of S. herbacea: o Using modern observations to infer past distributions

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Third map indicates that this willow plant was found further south – this suggests that the area was colder.

Approaches to Palaeoecology: -

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Common – descriptive palaeoecology (describing the components of ancient ecosystems) Autecology (study of individual species’ ecology) Synecology (study of populations, communities or whole ecosystems) Deductive Palaeoecology – this is less usual and relates to modelling what occurred in the ecosystem – it is used to simulate ancient ecosystems – e.g. BIOME model that reconstructs past vegetation, based on numerical modelling of fossil pollen data – see BIOME model results.. Experimental palaeoecology – this approach is very rarely used. It involves manipulating elements of a modern ecosystem to test possible effects on ancient ecosystem. e.g. Russian scientists have proposed the creation of a new wildlife park in north-eastern Siberia. This park would fence-in a high area of tundra to contain a large population of grazing mammals. Their theory is that the grazing mammals will turn the tundra back into steppe-tundra, as it was in the Pleistocene when megafauna grazed there.

What information do you need to undertake palaeoecological investigations?: -

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Requires various data and an understanding of the site and how the sediments formed. Site geology and stratigraphy: o Under what conditions did the sediments accumulate? o Were they fluvial, lacustrine, or wind-blown? (Most sedimentary columns contain combinations of these deposits) o How close was the ice margin of regional glaciers or ice sheet? o What was the temperature/precipitation regime under which they accumulated? Chronology: When did it happen? o Radiocarbon o U-series o Luminescence o Cosmogenic dating o Tree-ring dating o Tephrochronology Modern baseline Data: o Modern climate o Modern soils o Modern vegetation modern fauna o Are all useful for helping to understand the past and the geological and biological processes acting upon and within the environment

The Fossil Record – How is it preserved?: -

Taphonomy: the study of processes by which fossils become incorporated into sediment – there are certain laws of burial in the sense of how sediments are buried and preserved. Principles of Taphonomy o (the laws of burial) – only the tough/lucky survive

Only a tiny fraction of the organisms living at any one time become a part of the fossil record and are preserved o Upland organisms are rare, aquatic and riparian organisms are common in the fossil records – organisms are more likely to be preserved in water, as they are protected from the elements o Fossils do not always stay put – can get moved around the system – e.g. weathered fossil of a whale rib found on the beach in Spitsbergen – this was weathered and damaged, and also transported by the action of the sea. Diagenesis and weathering o Diagenesis – the post-depositional modification of sediment, the breakdown in-situ o Weathering – physical and chemical breakdown of rocks, fossils, etc, due to the exposure to ‘the weather’. o How to avoid there – if sediments that fall to lake bottom and are covered over with sediment, they will be entering an anoxic (no oxygen present) zone where bacterial decomposition is minimal. o Cold and dry areas are good for preservation as there is little moisture available therefore there is a reduced number of bacteria on the landscape that can cause deposition. o

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What gets preserved?: -

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Hard parts of animals (bones, scales, shells, exoskeletons) Very rarely sof tissue gets preserved as it decomposes more easily

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Bird, reptile and other vertebrate fossils: ofen found in caves, tar pits, lava tubes (Hawaii), packrat middens – e.g. owl remains found in caves. Insects: wing cases of beetles preserve really well Diatoms: o One celled algae that grow a shell (tests) made of silica o Abundant in fresh and saltwater sediments o Used to infer water conditions (salinity, temperature, trophic status and sea ice conditions

Fossil Mammals: o Bones and teeth (very resistant to decay) commonly preserved, but also (rarely) hair and mummified sof tissues o Dried remains in dry desert caves]Freeze-dried mummies in permafrost regions o Bog bodies – found in peat bogs – acidic peat bogs cause sof tissue to be tanned like leather and the bones and teeth dissolve due to the acidic conditions Oetzi the iceman: o Had sof and hard tissue as was kept in glacial conditions and this body was found high up in the alps o Oeggl et al. (2007) and references.. o Examined pollen from the body and compared with modern vegetation o Tried to reconstruct a map of past history of humans o Also produced a map of the past ecosystems o Investigated stomach contents, so know what was eating at the time, and know that the fossil has moved within the landscape. o Suggest that it was possibly shot at and then ran into the mountains to escape – shot with an arrow in head, but were unsure of where he actually died or how

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Fossils in permafrost: o Permafrost preserves fossils amazingly well o Frozen sediments greatly slow chemical weathering and prevent fossil abrasion o Mammal remains are sometimes mummified in permafrost, by having their moisture slowly drawn out – freeze dried o All of the fossils shown are all small infants and not fully grown animals – this could be because they fell in to the lakes more easily, or disease. o Also suggests that the small animals are frozen/buried quicker than larger ones and are therefore preserved better. Dried mammal dung o Preserved in dry caves o Contain plant macrofossils o Reveal animal’s diet and shows vegetation on the landscape at that time o Hyena dung Preservation of plants: o Wood (twigs, stems, branches, roots, bark) o Cones o Seeds (the most common and most useful) o Pollen (microscopic but tough and abundant) – Plant macrofossils: o Are larger than pollen o Fewer researchers, fewer populations o Provide a local story, not just regional o Specific identifications are ofen possible (as opposed to pollen) this is because the macrofossils look distinctive as the seeds are specific, so can identify plant species level o There are some exceptions – leaves are delicate and ofen do not preserve in Quaternary sediments o Where leaves are preserved, exceptionally low energy conditions must have been present Pollen: o Dominate the literature o Pollen preserves extremely well in lake sediments and bogs o It is easily obtained and counted o It provides a regional reconstruction of past vegetation Non-fossil evidence of past life: o Animal tracks o impressions of plants and animals in the mud

Where are fossils preserved?: -

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All parts of plants and animals are prone to decay and physical attack Anoxic conditions (waterlogged or rapidly buried): o Lakes o Peat bogs o Volcanic ash deposits o Ice o Fluvial deposits o Deltaic sediments Very arid conditions o Cave deposits Peat bogs: o A rich source of fossils o Plant macrofossils o Pollen o Snails, insects Lacustrine deposits: o Deposits formed in lakes, ponds, and kettle holes o Excellent sources of fossils o Shallow lakes ofen better than deep lakes, except in littoral (shallow) zones o Sediment preservation generally good, except in arid regions, where lakes dry up and sediments are eroded Ox-bow lakes:

Fluvial deposits: o Sediments laid down in streams o Fewer long-term deposits because of erosion of stream because of erosion of stream beds o Streams divided into riffles and pools o Erosion in riffles o Deposition in pools and backwaters

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Deltaic deposits: o Occur where a stream enters a lake o Organic detritus (flotsam) drops out of suspension o A rich source of fossils o Energy dissipates, the stream has energy so can transport sediment Rodent middens: o Some desert rodents build middens (piles of fecal pellets, plant materials, animal bones, insect remains, etc., cemented together by urine) These occur around the globe – rodents incorporate organic material into their nests. o Middens can persist in caves & rock shelters for many thousands of years o These provide the best archive of fossils for desert regions o Woodrats (packrats) in North America, stickrats in South America, hyrax in Middle East How is the fossil record interpreted? o Site stratigraphy is a critical element o If you don’t understand this, your reconstruction will be useless o You must know what has happened to the sediments (and the fossils they contain) since the time they were deposited. What makes a good archive? o Longevity: in the case of lakes:  The lake itself has to persist on the landscape for great lengths of time  Some lakes are short-lived features on the landscape, especially in drought-prone regions  When these lakes dry up, their sediments are exposed to the air, and erode away o Simplistic stratigraphy The ideal sediments: o Horizontally bedded o ‘lake-cake stratigraphy o No perturbations following deposition o Annually laminated sediment – Varves Troublesome stratigraphy: o Frost-heaved sediments o Bioturbated sediments o Slumped sediments o Sediments shifed by landslides o Sediments shifed by earthquakes o Sediments disturbed by past human activity (plowing, post-hole digging, etc.) Colluvial and Fluvial processes: o Colluvial processes: downhill movement of sediments

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o Fluvial processes: movement of sediments by flowing water Minimising troublesome stratigraphy: o Studying multiple sample locations o Side-scan sonar allows lake basin stratigraphy to be mapped remotely o Sediment mapping allows selection of deepest sediment profiles in the lake o Can also detect large-scale disturbance of sediments Rodent midden stratigraphy: o Good den sites continuously occupied o Erosion of midden layers difficult to detect o Only safe way: radiocarbon date each layer Cave Stratigraphy: o Stratigraphy in caves is frequently complicated: o Later occupation o Fluvial erosion o Changing foci of deposition

What is the future direction of palaeoecological investigation? -

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DNA from Quaternary mammals: o Barnes at el. 2002 – a paper on how glaciation impacts bear populations during the last glacial – e.g. data from bones and teeth. DNA was extracted from bones and teeth to see how the glacial activity impacted the bear communities over time – through radiocarbon dating and isotope data. Quantitative Palaeoecology: o Reconstructing the past: temperatures/precipitation/salinity/pH o Chironomids – fossilised heads of insects (midges) Cautionary information: o What are you trying to reconstruct o Plants and animals to respond to several factors rather than one o Changes in communities might relate to many variables Solving Data Problems: o High quality modern datasets o Careful site selection o Involve multiple species/proxies o Seek out all possible explanatory variables o Identify non-analogue situations...