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

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 Females

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

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)

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.

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.

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

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

Why male differences? 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)?)

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

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

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

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

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

Food hypotheses? 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.

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

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

Common ChimpsPygmy 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)

Common ChimpsPygmy chimps “parties” small, not stable Parties usually same sex Parties larger, more stable 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)

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