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Great Ape Ecology: The tale of two species

Great Ape Ecology: The tale of two species. Objectives. Discuss orangutans, gorillas, and chimpanzees Discuss the two different species or subspecies in each group Describe the ecological differences between them Understand how ecology influences behavior. Orangutans ( Pongo pygmaeus ).

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Great Ape Ecology: The tale of two species

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  1. Great Ape Ecology: The tale of two species

  2. Objectives • Discuss orangutans, gorillas, and chimpanzees • Discuss the two different species or subspecies in each group • Describe the ecological differences between them • Understand how ecology influences behavior

  3. Orangutans (Pongo pygmaeus) • S.E. Asia (Borneo and Sumatra) • Pongo pygmaeus pygmaeus (Borneo) • Pongo pygmaeus abelii (Sumatra) • Map from Delgado and van Schaik

  4. Females • Reach breeding age at 7 but usually don’t produce offspring until 11 years. • Gestation 9 months • Care for infants for 6 years • Interbirth interval is 8 years • Live up to late 50’s • Philopatric

  5. Males • Much larger than females • Two kinds of males- • Flanged- large, long calls • Unflanged- smaller, younger, • Reach adulthood around 8 years • Can force copulations with females • Disperse

  6. Ecology and Diet • Highly frugivorous, supplement with other foods. • Influenced by fruit availabilty- can store fat when fruit abundent • When fruit scarce, modify ranging- eat bark (cambium)

  7. Fruiting patterns • Mast fruiting (but otherwise not as seasonal). Happens 2-7 years. • May influence when females cycle. • Increase in grouping patterns. • Density of fruit sources influences density of orangs.

  8. Island differences (diet) • Sumatra • Overall density higher. • Feed more insects, less bark (graph 1) • Borneo • Lower density • Eat more bark and less insects. • Forest has higher soil fertility, more productive.

  9. Island differences (females) • Sumatra • More females travel in parties • More strangling figs (keystone resource) • Borneo • Less females travel in parties (graph) • Less fig resource, lower density of fruit patches

  10. Island differences males • Sumatra • Flanged males rarely force copulations (2.3%) • Long consortships (flanged) • Unflanged males don’t suceed often but try (45%) • Borneo • Both unflanged (90%) and flanged males (24%) force copulations • Flanged male consortships short

  11. Lower habitat quality (Borneo) means lower rates of association = shorter consortships, lower encounter rates. Borneo= more flanged males (1.6 more)than unflanged. Sumatra = about half as many flanged males as unflanged. (socially induced? Due to higher degree of sociality)?) Why male differences?

  12. Tool use • Seen only in the most dense Sumatran site. Social transmission? Neesia fruit

  13. Gorillas (Gorilla gorilla) • Sexual dimorphism • Mt. Gorilla = Gorilla gorilla berengei • Lowland = Gorilla gorilla gorilla (west) and G. g. grauri (east) (see map in Doran too

  14. LOWLAND MOUNTAIN • More frugivorous, not as available (pulpy) • More folivorous, little seasonality • Low level of Within group contest • Consume THV (terrestrial herbaceous vegetation) • Ranges around 500m/day • Seasonal changes in diet. • Ranges 1.3-2.6 km /day

  15. SOCIAL BEHAVIOR- Males LOWLAND MOUNTAIN • Groups a bit smaller (some seen with 32?) • Groups 2-25 • Males migrate (36%) - may tolerate sons (tenure 4-5 yrs) • Group size increases with degree of fruit eating. • Uni-male/multimale group (age) • Similar to Mt.

  16. SOCIAL BEHAVIOR- females LOWLAND MOUNTAIN • Similar to Mt • females migrate, sometimes more than 1x • However, more fission-Fusion. (40%) • Not very tolerant of other females • Mirrors fruit avail.

  17. THV- allows for larger group size (mt) and cohesion (mt). In lowland habitat, aquatic veg. Patchy as is other types of THV (fission - fusion) FRUIT- more competition, increases fission-fusion (WGC). Medium-Large patches can’t hold too many gorillas. Food hypotheses?

  18. Chimpanzees (Pan) • Sexually dimorphic • Large Communities (100+), • Fission Fusion • Dominance hierarchy • Use tools, actively hunt

  19. Common Chimps (P. troglodytes) Pygmy chimps (P. paniscus) • Feed on insects, vegetation, omnivore • Feed on fruit in large trees • Females not bonded, leave group • Females bonded, but leave group (g-g rubbing) • Female feed priority

  20. Common Chimps Pygmy chimps • Males bonded, have dominance • Males also have dominance but looser, • Not bonded • May have to do with distribution of females (larger stable groups- can’t defend)

  21. Common Chimps Pygmy chimps • “parties” small, not stable • Parties larger, more stable • Parties usually same sex • Mixed sex parties more common • Grooming more often male-male, less male-female (fig 3) • Grooming more often female-female, and male-female (fig 3)

  22. Hypotheses? • THV- more abundant and higher quality in pygmy chimp habitat. (but still patchy) • FRUIT- larger fruit patches allow for larger female parties among pygmy chimps

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