Chimpanzees & Bonobos
Diversity Within and Between
Species
Rebecca Stumpf
Introduction
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.
Ecology
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.
Diet
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
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:
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:
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.
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
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.
CONSERVATION
10,000-20,000
Bonobos
173,000 chimps
Extinct in Benin &
Togo
Conclusion
Chimps & Bonobos may not be so
behaviorly distinct as thought.
w/ genetic advances our understanding
of Pan expands.
Both possibly being on a continuum.