Differing impact of carnivores on bone assemblages in two East African Ecosystems Anna K....

Differing impact of carnivores on bone assemblages in two

East African Ecosystems

Anna K. BehrensmeyerDepartment of Paleobiology, Smithsonian Institution

Briana L. PobinerDepartment of Anthropology, Rutgers University

Goals:

Test the effects of different dominant carnivores on recent bone assemblages

Impact on models of carcass and prey availability for early hominins

Flesh slicer Bone crusher

Amboseli

Laikipia

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

wildeb

eeste

Burch

ell's

zebr

a

Grant

's ga

zelle

Thom

son's

gaz

elle

impa

la

buffa

lo

eleph

ant

giraf

fe

harte

bees

t

beisa

ory

x

black

rhino

eland

Fre

qu

ency

Laikipia

Amboseli 1970's

Laikipia and Amboseli: Live Census Data

Laikipia Amboseli

1975

2002

X

X X

Different Ecosystems

Dif

fere

nt T

imes

What is the taphonomic impact of different top predators?

11 transects12 transects

Variables to Compare:

• Average number of bones per individual

• Skeletal part survival

• Completeness of femora and humeri

• Damage to femora and humeri

• Juveniles vs. adults

Burchell’s zebra only

Laikipia Ecosystem

Laikipia Lions on Zebra Prey

Amboseli Ecosystem

Predators of Amboseli Park1975 - 2003

Amboseli: Change in Patterns of Destruction Same transects, 1975 and 2002

Bo

nes

/ Ind

ivid

ual

0

5

10

15

20

25

30

35

1 2 3 4 5 6

Increased Body Size

HR, RO GAZ, IM WB, CW BF HP, RH EL ZB GF

1975

2002

• Diverse predatorsLions dominant

Few hyenas

Lions absent• Hyenas increasing

• Many hyenas• Few lions

1975

1990

2002-2003

• Abundant carcasses• Low damage levels

•Abundant carcassesFew zebra deaths

• Fresh carcasses rare• 71% decrease in bones

High damage levels

Ecosystem Taphosystem

Amboseli

Hyena dominance and intraspecific competition is driving the change in carcass and bone survival.

Working hypothesis:

If the top predator controls the destruction patterns of prey skeletons, then Laikipia 2002 should be more similar to Amboseli 1975 than Amboseli 2002-03.

Laikipia Amboseli

1975

2002

Lion

Lion Hyena

Different Ecosystems

Dif

fere

nt T

imes

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

Ambo 1975 Ambo 02-03 Laikipia 02

Bo

nes

/ MN

I

Average Bones per MNI

Zebra Skeletal Part SurvivalAmboseli 1975 and 2002-3 vs. Laikipia 2002

Ob

serv

ed

/ E

xp

ecte

d

Sku

ll

Jaw

(h

emi)

Ve

rteb

rae

Rib

s

Sca

pul

a

Hum

eru

s

Rad

ius/

uln

a

Met

aca

rpal

Inno

min

ate

Fe

mu

r

Tib

ia

Met

ata

rsal

Pa

tella

Po

dial

s

Ph

alan

ges

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45Laikipia 02 MNI = 27

Ambo 1975 MNI = 45Ambo 2002-3 MNI = 36

Forelimb Hindlimb

0.00

0.10

0.20

0.30

0.40

0.50

0.60

Whole Prox.–DistalPair

Shaft only

Prox. only

Prox. +

Shaft

Distal+

Shaft

Distal only

Fre

quen

cyCompleteness of Humerus and Femur

Laikipia 02 (N = 9)

Ambo 75 (N = 48)

Ambo 02-03 (N = 17)

D: Fragments only

B: Moderate: marginalgnawing; one end absent

A: Minimal: tooth marks,scoring

C: Heavy: both ends gnawed or absent

Damage Categories

Damage to Humerus and Femur

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

No Damage

AMinimal

Fre

qu

en

cy

Increasing damage

Ambo 75 (N = 48)

Ambo 02 03 (N = 17)

Laikipia 02 (N = 9)

BModerate

CHeavy

DFragments

Adults vs. Juveniles

0

5

10

15

20

25

30

35

Ambo 1975 Ambo 02 - 03 Laikipia 02

MN

I

Adult

Juvenile

Laikipia Amboseli

1975

2002-03

Lion

Lion Hyena

Dominant Predator

Conclusions

Laikipia 2002 bone assemblage more similar to Amboseli 2002-03 than to Amboseli 1975.

Our prediction is not supported. Lion vs. hyena dominance does not leave a clear taphonomic signal in the bone assemblage based on the variables we used.

New Hypothesis: Damage levels may be better indicators of overall predator pressure on the prey populations than the signature of the dominant predator(s).

Skeletal part survival affected by:• bone-processing capabilities of predators

…but also probably by:• intraspecific competition for prey • predator social structure• predator diversity

Carcass availability and damage patterns can change over decades.

Carcasses (and prey) available to early hominins would have varied greatly in time and space because of variablity in predator consumption of carcasses.

Recognition of this variability could have been an important adaptive strategy for meat-seeking hominin individuals and groups.

With Thanks to:

The National Museums of KenyaThe Kenya Wildlife Service

The National Geographic Society

David Western, Dorothy Dechant, Richard Leakey, andall the individuals who have helped with Amboseli bone research

Fulbright-Hays Fellowship to B. PobinerSweetwaters Game Reserve, Laikipia, Kenya