global modelling of megafaunal extinction climate and colonisation: results from a high resolution...

Global Modelling of Megafaunal Extinction

Climate and Colonisation:Results from a high resolution analysis

Lewis Bartlett1,2, Andrea Manica2, Graham Prescott2, David Williams2, Andrew Balmford2 & Rhys Green2

1 Environment and Sustainability Institute, University of Exeter; 2 Department of Zoology, University of Cambridge.

Research Premise:A Global Analysis for a Global Phenomenon

• Need for global, integrative assessment of extinction – builds on work of Prescott et al. 20121

• Split globe into zones: map extinction, expansion, and climate

• Compare predictive power of climate and early humans– 80,000 year analysis; 4000 year time steps

1 Prescott et al 2012, Quantitative global analysis of the role of climate and people in explaining late Quaternary megafaunal extinctions. Proc. Natl. Acad. Sci.. 109, 4527–4531

Extinct Surviving

Research Premise:Assembling Global Datasets

Size of circle represents taxonomic abundance

Analysis

• Non-linear models: climate only, human only, and combined - iterate over many re-sampled datasets

• Predict human impact using arrival and zone area

100

60

20

80

40

0Early Human

ArrivalLate Human

Arrival

Per

cent

age

Var

iatio

n E

xpla

ined

(Nag

elke

rke’

s R

2 )

Unique to Humans

Unique to Climate

Shared

Explanatory Power:

Results:Overall Global Model Performance

Results:Predicting in sequence…

Results:…predicting one major effect…

Results:… predicting in parallel …

Results:… or indeed not at all

Interpretation & Direction

• Strongly implicates human colonisation– More informative predictor than climate

• Asia: the next frontier– Well studied zones resolved: look to zones we

don’t explain

Thank You for Your Attention!

Any Questions?

l.bartlett@ex.ac.uk

Start of Arrival Time Step (ky BP)

Africa Papua Australia Tasmania Indo-Malaya Japan Madagascar Alaska & Canada North America New Zealand Europe Siberia Central Asia South America80 60 60 44 64 24 8 20 20 4 48 48 80 1680 44 44 44 48 24 8 16 16 4 44 48 72 1280 56 56 44 64 24 8 16 16 4 48 48 80 1680 56 56 44 64 24 8 16 16 4 48 48 80 1280 52 52 44 64 24 8 16 16 4 48 48 80 1680 52 52 44 64 24 8 16 16 4 48 48 80 1280 48 48 44 64 24 8 16 16 4 48 48 80 1680 48 48 44 64 24 8 16 16 4 48 48 80 12

Human Arrival Scenarios

logit(prob.extinction)= a*(1+b/LogArea)*T.Human*exp(c*(1+d/LogArea)*T.Human)

Predicting Human Effect

where ‘T.Human’ is time since human arrival

Function based on the Ricker Model for population density