Chimpanzees & Bonobos Diversity Within and Between Species

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Chimpanzees & Bonobos Diversity Within and Between Species

  • Rebecca Stumpf


  • Studies of Chimpanzees

  • (Pan troglodytes) & Bonobos

  • (Pan Baniscus) started in the 60s and 70s

  • with discoveries about the vast diversity

  • Within & b/w species of Pan genus.

  • Continuous research of these include

  • ecology, culture, genetic & demographic

  • variation. Following is an analysis of

  • Taxonomy, morphology, ecology and sexual

  • Behaviors of wild Chimps & Bonobos.

Chimpanzee & Bonobo Research: A Historical Perspective

  • Chimp field studies began in the 60s w/ Jane Goodall at Gombe Streme Reserve & Toshisada Nishida in Mahale Mnt. NP, TZ.

  • These studies focused on life, diet, intergroup social interactions and was the corner stone of chimp behavioral research.

  • Dstrib.: equatorial Africa, habitats very fragmented w/ diff. been seen b/w east & west pop. Adding complexity to chimp grouping patterns, behavior, feeding ecology w/in subspecies.

  • Bonobos less studied due to Congo civil war. Field data comes from Lomako & Wamba or captive pop whose behavior differs from chimps in dominance patterns, aggression, sexual behavior and intercommunity interactions. Yet they show behav. overlap.

  • Some behaviors as lethal aggression took years to discover.

  • Bonobo studies started in drier open habitats, this may influvence behav. variation

Changing Taxonomic Perspectives

  • In the past GA = Pongidae

  • Today: Hominidae,

  • Previously reserved for

  • humans and ancestors.

  • Genetics show chimps &

  • Bonobos are more closely

  • related to humans than

  • to other GA so they are in

  • the Hominini tribe w/ humans.

  • Bonobos were recog. diff.

  • from chimps in ’29 ltr placed

  • in separate species

  • (in morph/gen). Split b/w

  • Spe. 1.7 – 2.7 mya and 1.6 mya

  • b/w the 4 chimp subspe. Bonobo

  • Less gen. diverse.

Morphological Variation

  • Pan males: bigger canines,

  • Larger body mass, Bon 15%

  • More than females, chimps

  • 5-14% more. P.t.t. largest most

  • Dimorphic.Bon. Slender build,

  • longer thigh bones, muscles,

  • Feet w/ crania/mandible

  • distinct from chimps & higher

  • pitch vocals. Facial patterns: babies

  • Pink in chimps, P. t. verus black

  • braw ridge lighter face, P. t. t. face pitch

  • black in adults. Bon. Face black forever

  • w/ pink lips, middle parted hair. Both born

  • with bottom tuft of white hair.


  • Habitat/Disrib: Chimps

  • - Diverse; dense lowland tropical

  • rain forest, savannah

  • woodland, altitude 3000 m

  • From Senegal to DRC

  • to TZ. P. t. s. may have

  • Moved to seasonally dry

  • habitat recently. Bon –

  • Lowland rainforest, dry forest,

  • & grassland. Limited in

  • Congo river triagle. Pan spe.

  • don’t overlap sepa. 1.5 mya by river

  • coincides w/ hominin speciation

  • from climate habitat change.


  • Chimps & Bonobos very

  • frugivorous and eat high terrestrial

  • herbaceous vegetation (THV),

  • ea. Chimps rely on fallback food

  • in times of shortage. Plant spe.

  • Varies depending on season, in scarcity leaves,

  • wide range and low qual. food taken. Dry areas

  • limit food. Animals: 8-10% of chimp diet

  • varies b/w sites. 1-3% mamals. Chimp/gorillas

  • overlap food similar but changes in scarcity.

  • Bon. Food very varied w/ ripe fruit, high protein

  • plants and 1% animals. Hunting in all chimp sites varies

  • in kind of prey, habitat traits and methods b/w sites. Red colobus liked where available,

  • 17 spe. In Mahale, 5 in Taï. Gombe like immature monkeys, Taï like adults.

  • >50% of hunts successful, depending on forest cover, is lower in continuous canopy. In east indiv. Hunt opportunistically as trees interrupted, in west cooperative hunting needed. Chimp males hunt more than females, & frequency varies w/ food avail, estrous females, group comp. Hunting assoc. w/ larger groups and more fruit. In Ngogo estrous females don’t affect male hunting or males having higher mating success. Hunting assoc. w/ more males in party. Feeding competition doesn’t limit grouping so is not just for subsistence. Bon. Rarely hunt if they do its duikers.

Social Organizations & Grouping Patterns

  • Affected by eco factors, ea. Chimps have

  • Dry season the others have few which affect

  • food avail. Habitat diff. and seasonality affect female grouping patterns & social behaviors in Pan. Community Structure: chimp/bon. Multi male/female struc. Community varies from

  • 5 to 150 && Bo. 25 – 75 or 120. Males philopatric remain in birth group. Females transfer to other communities w/ sexual maturity to avoid

  • inbreed. Female chimps in new group estab. Relat. w/ males, local females aggressive. Young female bon. Immigrating make ties w/older femles for integration. Femaletransfer likelihood varies from sites affected by isolation or benefits of remaining for getting moms area. Male transfer seen twice.

Ranging Patterns, Day Ranges & Nesting

  • Ranging Patterns, Day Ranges & Nesting

  • Chimp home ranges larger than for other GA w/ variation b/w sites w/ smallest in Gombe 10 km² to over 50 km² in Senegal this may be due to pop density or male # in community. Male & femles differ in day range & patterns. Males have larger day ranges & estrous females travel w/ larger groups w/ males. W. African chimp females assoc w/ males & females and use all range. E. females less social than males spend most time w/ children, other mothers and theirs when not in estrous they don’t use all range as males w/ lower assoc rates. All make nest from woven branches at night reused w/few trees

  • More to

  • talk about…

Grouping patterns & Variation in Party Size:

  • Grouping patterns & Variation in Party Size:

  • Eco factors, predation & estrous influence grouping w/ dependance on fruit a challenge. All have fission fusion social system, indiv. Form small subgroups that change in size thru the day this may limitinfra group feed competition 7 better foraging. Small groups form in scarcity & unitein abundance. Party comp. influenced by estrous & become larger w/ those females. Bon. Party seems to not be linked in such but males increase in number w/ estrous females present. Predation risk affected by party size that gives vigilence, protects indiv. Their size & strength enables smaller group foraging but unit at night. Bon. Stay together in large groups rarely aalone w/ food avail influencing group size, more food less competition. W. African chimps rarely alone form larger parties may be due to eco diff. Group> when reliance on thv high along w/ diet diversity. All female parties more common in Bon & males leave when food low. East chimp groups contain mostly males.

Intragroup Social Relationships:

  • Intragroup Social Relationships:

  • Chimps present strong male-male bonds & male dominance assoc more grooming w/ each other reciprocally w/ hierarchy which rise w/ status. They join in mate guarding, hunting, prey capture & cross group aggression too (not neces kin based). Sharing food b/w them a& some high status females. Males rely on same age coalitions w/ rank relations, coalitions maintain rank. Dominance is important as they have more children. Males tend to be more aggressive b/w each other but females also affected & affecting. In group killing seen & may lessen competition.

  • Females assoc weak due to transfers or food competition & depending on hierarchy (Tai). In west chimps & bon. Competition leads to female alliances. Hierarchies in females determine birth success, body weight & Inter birth intervals. Dominant females walk together, help in competitions & getting best sites thus getting more birth success. In cases of infanticide lower ranking females are victims. Aggression amongst them occurs about food & child defense. In bon. Communities its diff. females are the dominants w/ female assoc most important even taking food from males and chase them away, whilst males aren’t as sharing amongst themselves.

  • Grooming starts b/w sexes, followed by same sex grooming. Male hierarchies less important for Bon & don’t assist eachother in fights yet console more.

Bon/ Chimp mothers affect son dominance yet bon mother son dependency is longer.

  • Bon/ Chimp mothers affect son dominance yet bon mother son dependency is longer.

  • In social systems chimp male philopatry affects the strong bond in grooming, patroling & sharing yet in Tai there is bisexual bonding

  • Intercommunity Interactions:

  • Chimps are very territorial w/ interactions of such hostile or fatal, they patrol their bordersonce a month meeting other communities in 26-40% o times other times avoiding the periphery. Patrols are all malein east and mixed in west Tai, yet females rarely engaging in attacks W/ killings seen more in the east this is linked to food access and female birth success. In encounters reactions depend on group size, yet smaller groups may approach showing need to protect resources. In case of many against one the result is fatal. Yet differing if female then grooming, attacking or mating may occur. Bon defend their territories but encounters b/w communities are less aggressive & last hours, males not seen patroling & encounters are in the center of territory not peripheral..


  • Infanticide:

  • Seen in most long term sites w/I & b/w communities, in Mahale 16% of deaths were these & killed by mature males. B/w group events may reduce competition or keep females away from borders. May be strategy for higher reproductive success & shorten IBI. The wests two sex bonding may prevent infanticide.

Reproductive Parameters

  • Reproductive Parameters

  • Difference in Reproductive Parameters w/in Pan:

  • Chimps give birth every 5-6 yrs, in Bon IBI is shorter.

  • Resumption of cycling varies b/w east/west. W/ cycling sesonal in Gombe after dry season. Chimps have 35 day mesnstral cycle they are sexually active phase is 10-15 days of estrus marked by pink large swelling yet most sexual relation are non reproductive w/ promiscuity to avoid infanticide.

  • In bon. Almost all mating is initiated by males and in chimps 1/3 by females. In bon there is same sex behavior mostly female. Chimp females can chose mates by manipulation.


  • 10,000-20,000

  • Bonobos

  • 173,000 chimps

  • Extinct in Benin &

  • Togo


  • Chimps & Bonobos may not be so behaviorly distinct as thought.

  • w/ genetic advances our understanding of Pan expands.

  • Both possibly being on a continuum.

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