Transcript Diatom_Insect

Non-marine biological evidence
Chapter 8
Non-marine biological evidence
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Plant Macrofossils
Diatoms
Insects
Ostracods
Plant Macrofossils
• Advantages: usually identifiable to the species
level and easily dated.
• Disadvantages: fewer specimens relative to
pollen, typically provides a discontinuous
record.
• Used to assess fluctuations of tree-lines.
• Unlike pollen, macrofossils are transported for
very short distances. Thus, they provide better
information on tree-line movement.
Plant macrofossil-Artic
Plant macrofossil-Alpine treeline
Diatom-based paleoclimatogical
reconstructions
• Diatoms: Unicellular
algae present in
freshwater and marine
systems.
• Found in polar,
temperate, sub-tropical,
and tropical regions.
Diatom-based paleoclimatogical
reconstructions
• Based on the concept of
ecological niche (a given
population is adapted to
survive and reproduce
under a set of biotic and
abiotic conditions).
• A niche can be devised as
a multi-dimensional space
in which the axes
represent variables.
• In paleoclimatology, useful species are
those with limited niches; whose
abundance, distribution, and presence or
absence are controlled by climatic factors.
• However, one needs to keep in mind that
niches are dynamic and transient and that
species can evolve and adapt.
• There are three main approaches to
reconstruct paleo-climates:
– Indicator species approach: relies on the
occurrence of species with known modern
environmental tolerances.
– Assemblage approach
– Transfer function approach
• Indicator species approach: relies on the
occurrence of species with known modern
environmental tolerances (benthic vs.
planktonic).
• Assemblage approach: Based on modern
analog techniques, where fossil and modern
assemblages are statistically compared.
• Transfer function approach: modern taxa at
different sites (Y) and environmental
variables (X) are compared to obtain of a
function of the form: Y= f(x) + variance.
f(x) is estimated by linear, non-linear, and/or
multivariate regressions.
• Numerical techniques are employed to
reconstruct temperature, pH, and salinity.
• Lakes are sampled for diatoms and
measurements of temperature, pH, salinity,
etc are performed simultaneously.
• Statistical methods (e.g., multi-component
analysis) provide numerical relationships
between diatoms and climatic parameters.
• Assumptions:
– Modern taxa is related to the environment.
– The measured environmental variables are ecologically
important.
– Transfer functions adequately model the response of
modern taxa to the measured environmental variables.
– Fossil taxa responded in a fashion predicted by the
transfer function.
– Non-measured variables play a negligible role.
Detrended Canonical
Correspondence
Analysis (DCCA).
Larocque and Bigler (2004)
Larocque and Bigler (2004)
Insects
• Midge flies (chironomid)
are used to reconstruct
temperature.
• They have a narrow
ecological range, they are
commonly present in
aquatic systems, they are
abundant, and they
respond quickly to changes
in temperature.
Insects
• Problems:
Chironomids likely reflect water
temperature rather than
surface temperature.
Because they can only be
identified to the genus level,
site-specific calibrations are
needed.
Unknown effect of pH, salinity,
lake/pond depth, nutrients.