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Differing impact of carnivores on bone assemblages in two East African Ecosystems. Anna K. Behrensmeyer Department of Paleobiology, Smithsonian Institution Briana L. Pobiner Department of Anthropology, Rutgers University. Flesh slicer. Bone crusher. Goals:
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Differing impact of carnivores on bone assemblages in two East African Ecosystems Anna K. Behrensmeyer Department of Paleobiology, Smithsonian Institution Briana L. Pobiner Department of Anthropology, Rutgers University
Flesh slicer Bone crusher Goals: Test the effects of different dominant carnivores on recent bone assemblages Impact on models of carcass and prey availability for early hominins
Laikipia and Amboseli: Live Census Data 0.45 Laikipia 0.40 Amboseli 1970's 0.35 0.30 Frequency 0.25 0.20 0.15 0.10 0.05 0.00 eland giraffe buffalo impala elephant hartebeest beisa oryx black rhino wildebeeste Grant's gazelle Burchell's zebra Thomson's gazelle
What is the taphonomic impact of different top predators? Different Ecosystems Laikipia Amboseli 2002 X X Different Times 1975 X 12 transects 11 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
Laikipia Lions on Zebra Prey
Predators of Amboseli Park 1975 - 2003
Amboseli: Change in Patterns of Destruction Same transects, 1975 and 2002 1975 Bones / Individual 2002 HR, RO GAZ, IM WB, CW BF HP, RH EL ZB GF Increased Body Size
Amboseli Ecosystem Taphosystem • Diverse predators • Lions dominant • Few hyenas • Abundant carcasses • Low damage levels 1975 1990 2002- 2003 • Lions absent • Hyenas increasing • Abundant carcasses • Few zebra deaths • Fresh carcasses rare • 71% decrease in bones • High damage levels • Many hyenas • Few lions
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. Different Ecosystems Laikipia Amboseli 2002 Lion Hyena Different Times 1975 Lion
Average Bones per MNI 16.00 14.00 12.00 10.00 Bones / MNI 8.00 6.00 4.00 2.00 0.00 Ambo 1975 Ambo 02-03 Laikipia 02
Laikipia 02 MNI = 27 Ribs Skull Tibia Femur Patella Podials Scapula Humerus Vertebrae Metatarsal Phalanges Jaw (hemi) Metacarpal Innominate Radius/ulna Zebra Skeletal Part Survival Amboseli 1975 and 2002-3 vs. Laikipia 2002 0.45 0.40 Ambo 1975 MNI = 45 Ambo 2002-3 MNI = 36 0.35 0.30 0.25 Observed / Expected 0.20 0.15 0.10 0.05 0.00 Forelimb Hindlimb
Laikipia 02 (N = 9) Completeness of Humerus and Femur 0.60 Ambo 75 (N = 48) Ambo 02-03 (N = 17) 0.50 0.40 Frequency 0.30 0.20 0.10 0.00 Whole Prox.– Distal Pair Shaft only Prox. only Prox. + Shaft Distal + Shaft Distal only
Damage Categories A: Minimal: tooth marks, scoring B: Moderate: marginal gnawing; one end absent C: Heavy: both ends gnawed or absent D: Fragments only
0.70 Laikipia 02 (N = 9) 0.60 0.50 0.40 0.30 0.20 0.10 0.00 Increasing damage Damage to Humerus and Femur Ambo 75 (N = 48) Ambo 02 03 (N = 17) Frequency A Minimal B Moderate C Heavy D Fragments No Damage
Adult Juvenile Adults vs. Juveniles 35 30 25 20 MNI 15 10 5 0 Ambo 1975 Ambo 02 - 03 Laikipia 02
Laikipia Amboseli Dominant Predator Lion 2002-03 Hyena 1975 Lion
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 Kenya The Kenya Wildlife Service The National Geographic Society David Western, Dorothy Dechant, Richard Leakey, and all the individuals who have helped with Amboseli bone research Fulbright-Hays Fellowship to B. Pobiner Sweetwaters Game Reserve, Laikipia, Kenya