Palaeoecology Flashcards
(36 cards)
What is palaeoecology?
Palaeoecology is the study of past ecosystem which may or may not exist in the modern world. It is also the study of interactions between past living organisms and their environment.
What sort of changes can we reconstruct through palaeoecology?
Flora, Fauna, Climate and the impact of people on the environment. This is limited by the availability of floral and faunal evidence.
What are macrofossils?
These are whole skeletons to small fragments of animals or plants, we identify these by eye or magnification. Smaller remains are preserved in larger quantities so we can get a more complete dataset for smaller fossils.
What are microfossils?
These are minute remains, e.g. pollen, ostracods, diatoms. We magnify these over 400x to see.
Founding assumptions of palaeoecology
- Uniformitarianism: present is the key to the past and to what might be happening in the future.
- We need modern analogues.
- Speed of change is ignored.
- Does not recognise time-transgressive change.
- Controlling environmental factors on the analogue are known.
- Ecological affinities remain constant.
- Assumes populations are/were in equilibrium.
- Assumes modern analogues exist for past species/environment.
- Process of fossilisation is known.
- No contamination or differential preservations.
- Hence palaeoecology is not always spot on.
What might reduce the evidence in the fossil record?
- Seasonal migration of organisms.
- Exotic organisms may stray into ecosystem.
- Some corpses are predated after death.
- Decay or erosion may destroy record.
- Only a few organisms remain well-preserved.
Faunal Evidence: Vertebrates
Bones of vertebrates tend to be big and easily diagnostic: tusks, teeth.
Hair and horns also preserve well, and coprolites (droppings) give evidence about climate, environment and what the species ate.
What characteristics enable good preservation?
Frozen places, e.g. Siberia preserve very well. A baby wooly mammoth was found after 39,000 years.
Dry environments where dessication and drying out preserve fossils and vertebrates.
Amber can also preserve small things such as hair.
Limitation of Vertebrate evidence
- Identification can be difficult with small, poorly preserved fossils.
- Remains are rare as preservation is sparse, and will only become more sparse.
- preservation may be unrepresentative, due to sporadic preservation sites. Taar pits in LA upwell fumes that animals fall into.
- Fossils can be transported by predators or erosion.
- Rapid evolution or extinction cause changes in ecological affinities and cause disequilibrium.
Advantages of Vertebrate Evidence
- Age easily determined using radiocarbon dating, or uranium-thorium dating.
- Can determine diets through isotopes and minerals in teeth, bones or coprolites.
- DNA detection (Gilbert et al., 2007 on mammoth hair DNA).
- Strong ecological preferences and affinities)
- Size is related to climate (Bergmann’s Rule).
What is Bergmann’s Rule?
Body size increases as temperature decreases to help conserve energy.
I.e. volume grows more rapidly than skin area (heat production vs heat dissipation).
How can we see differences between interglacial periods through vertebrate evidence?
We know animals migrate to warmer regions during glacial periods, and they move back north when it warms. The spatial distribution of vertebrate evidence can be assessed to identify between glacials and interglacials.
Invertebrate forms of Evidence
Terrestrial: molluscs (snails), coleopteran (beetles)
Aquatic: Molluscs (snails/clams), Ostracods (crustaceans), Chronimids (midges), Cladocera (water fleas).
What controls the presence and distribution of invertebrates?
Chemical: pH, salinity, dissolved oxygen, trophic nutrient level, solute composition.
Physical: substrate, presence of plants, water movement, temperature, depth.
The low tolerance to change in these properties make invertebrates good for understanding climate changes.
Many of these properties are interdependent.
What are foraminifa?
These are microscopic single-celled organisms, that coil in one direction is sea water is above 9 degrees, and the opposite way in colder seas, hence these records can indicate sea temperature.
Forams can be planktonic or benthic, which means they reside at the surface or bottom of the sea respectively.
Why are coleoptera a good modern analogue?
Their head capsules preserve well, and cover all sizes and shapes so are easily identifiable.
Beetles are STENOTHERMIC meaning they are ecologically temperature controlled.
Many are STENOTOPIC which means they show a marked preference for particular environments (Lowe & Walker)
They also travel long distances and have a low rate of evolution, making them good for understanding past changes.
How do we use a mutual climatic range approach with coleoptera?
If you find three beetle species in an assemblage, you can overlap their climatic ranges to find a tight window in which they all could exist.
What is pollen?
Pollen consists of a cell, intone and extine. The waxy extine helps preserve pollen grains.
The pollen of a plant is usually very distinct in shape and colour.
How is pollen dispersed?`
By wind (anemophilous), insects, birds and animals (entomophilous/zoophilus). Aquatic pollen is dispersed by water and self fertilisation.
What features of pollen make it a good evidence source?
The extine is very resistant to decay, its morphology varies between species.
It evolves extremely slowly, a principle of uniformitarianism.
Produced in very high numbers and disperses well, reflecting the natural vegetation of a location.
Controlling Factors on Pollen production and dispersion.
- Location of refugia: distance and presence of physical obstacles.
- Rates of migration: method of pollination and/or seed dispersal: trees migrate very slowly, but depends on species.
- Temperature tolerance varies between species.
- Inter-species competition can control species population rather than climate.
- Soil maturity, some soils may not be able to facilitate certain biological processes.
Is there a lag time between climate and vegetation?
Yes. They are out of equilibrium by 1-2,000 years. This is likely to be longer during the transition from cold to warm, as trees have to migrate long distances, whereas in a cooling climate trees will hang on.
Problems with using Pollen?
- Some uniformitarian assumptions as before.
- Not all plants produce the same amount of pollen. Self-fertilizers don’t produce much so finding 1-2 grains may indicate there was a lot of them.
- The method of dispersal varies, wind can carry pollen grains a great distance away from where it was growing: you can have over and underestimations of the plant population.
What plant types ‘break the rules’ in terms of pollen production?
- Culluna Vulgaris (heather) produces lots of pollen although it self-fertilizes.
- Fagus (beech), Quercus (Oak) don’t produce as much pollen as expected.
- Triticum (wheat) is self pollinating but produces reasonable amounts.
An index of relative production has been created to correct for pollen production rates.
