Accounting for uncertainty when estimating Pleistocene megafauna extinction times

Accounting for uncertainty when estimating Pleistocene megafauna extinction times
Corey J. A. Bradshaw1,2, Barry W. Brook1, Chris S. M. Turney3, Alan Cooper1,4
1THE ENVIRONMENT INSTITUTE, University of Adelaide; 2South Australian Research & Development Institute; 3School of Geography, University of Exeter; 4Australian Centre for Ancient DNA

extinction must be inferred from record of sightings/collections
when a species becomes increasingly rare before extinction, might persist unseen for many years
so the time of last sighting often poor estimate of extinction date
x
x
x
x
x
x
x
x
x
x
x
?
?
present
past
Roberts & Solow 2003 Nature 426:245

optimal linear estimation
joint distribution of k same Weibull form regardless of parent distribution
estimated extinction time q
L: symmetric k×k matrix
n: Estimated shape parameter of joint Weibull distribution of k
CI
q
x
x
x
x
x
x
x
x
x
x
x
present
past
Roberts & Solow 2003 Nature 426:245

maximum likelihood to account for radio carbon dating error
assume true ages U independent/uniformly distributed over (b1,g1) where b1 = extinction date
PDF of Xj:
b1
x
x
x
x
x
x
x
x
x
x
x
present
past
Solow et al. 2006 PNAS 103:7351

but... previous sighting rate important
length of period since last sighting informative
given previous sighting rate(n/tn), probability of next sighting
where p drops below threshold with increasing T-tn, TE inferred
TE
x
x
x
x
x
x
x
x
x
x
x
present
past
McInerny et al. 2006 ConservBiol20:562

but... TE depends on number of samples in ‘final’ period
declining influence of dates within time since last sighting
sequentially recalculated TE, weighting by cumulative distance from T1
T1
TE
x
x
x
x
x
x
x
x
x
x
x
present
past

but... TE depends on number of samples in ‘final’ period
declining influence of dates within time since last sighting
sequentially recalculated TE, weighting by cumulative distance from T1
T1
TE
x
x
x
x
x
x
x
x
x
x
x
present
past
x
x
x
x
x
x
x
x
x
x
x
now simply combine methods with Gaussian resampler within carbon date errors for each record

now simply combine methods with Gaussian resampler within carbon date errors for each record

exponential
‘true’
extinction
linear
sigmoidal
logarithmic
uniform

uniform
linear
sigmoidal
exponential
logarithmic

Glacials, Interglacials, Stadials and Interstadials
stadial
interstadial
Interglacial
Glacial
Interglacial

Extracting An Ice Core

Annual Layers In Ice Core

Cariaco Basin Bathymetry
water exchange with the open Caribbean Sea is restricted
intense seasonal productivity and high sedimentation rate
anoxic below 300 m
limited bioturbation (post-depositional mixing of sediments by marine life)

Mw-rs ~ -83+ 0.98 × AMS

Interstadials – OXCAL wPDFs
extinctions - unconstrained
P(rand overlap = 0.12)
combined ext/app P(rand overlap) = 0.13
extinctions - constrained
P(rand overlap) = 0.09

Interstadials – OXCAL raw dates
extinctions - raw dates
appearances – raw dates

Stadials – OXCAL raw dates
extinctions - raw dates

Accounting for uncertainty when estimating Pleistocene megafauna extinction times

by Conservation Bytes on Jun 25, 2010

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Accounting for uncertainty when estimating Pleistocene megafauna extinction times — Presentation Transcript