Primates Pt.2 Flashcards
Anatomical traits and
behaviour linked
– e.g. male-male competition &
sexual dimorphism in body size
and canine size
Behaviour is a product of
natural selection on ancestral
populations resulting in
increased adaptation to
particular habitat
Socioecology
Socioecology: the approach
that explains variation in the
social systems of animals with
reference to ecological and
biological factors
Availability and distribution of
resources affects what
Availability and distribution of
resources → – competition – grouping – social behaviour – mating patterns
Social behaviour is a suite of
adaptations to the ecological
and social environment
what is needed for For survival and fitness?
– Find food
– Find and co-ordinate with mate
– Have offspring & rear offspring
– Avoid parasites & diseases
– Avoid predators
Costs of group living
(sociality)
– increased competition for
resources (food, mates)
– increased likelihood of
disease and parasite
transmission
– increased conspicuousness
(predation)
Benefits of group living
(sociality
– defense of territory/food
resources & mates from
competitors
– lower risk of predation
Benefits of sociality: Lower risk of predation
- Detection
- more eyes to detect predators
- Deterrence
- more individuals to mob or chase
predators away - Dilution
- smaller chance that any one individual
is the prey of the day when group is
larger-
Optimal group size
- The size and
composition of groups
reflects a compromise
between the costs and
benefits of sociality
for individuals
– magnitude of these
costs and benefits is
influenced by social
and ecological factors
Males vs. females (4)
Females compete over food
Males compete over females
Reproductive success limited by:
Females:
Access to resources
Males:
Access to females
Ecological pressures influence the distribution of females, and
males distribute themselves to maximize their access to females
High metabolic costs associated with
gestation and lactation
Food
- Supplies energy
requirements for survival,
growth & reproduction - Dietary specializations
drive numerous
specializations
– body size
– teeth form and number
– gut length
– hand (shape, function)
– locomotor and suspensory
systems
– brain size - Different kinds of foods in
different kinds of habitats
are distributed differently
in space and time
Diet correlated with body size in primates
Insectivores are
smaller than
frugivores &
frugivores are smaller
than folivores
Differences in size are
related to differences
in energy
requirements
Adaptations in the digestive tract
Primates unable to
digest cellulose →
microorganism for
cellulose digestion
Colobines: complex
multi-chambered
stomach with
cellulose-digesting
bacteria
Diet and brain size
‘Ecological intelligence hypothesis’
- Frugivorous primates
relatively larger brains than
folivorous - → Frugivorous primates
need larger brains to
remember location and
phenological status of fruit
trees
Distributions of resources and defensibility: Clumped distribution
→ May be defended
→ Territoriality
Distributions of resources and defensibility: Even distribution
→ Difficult to defend
→ Home ranges without defence
Resource competition: Cost of forming (large) groups
Negative effects on
energy
budgets
development
reproductive
performance
Resources determine type of competition * Scramble (‘first come first serve’)
Food is evenly distributed
Amount of food available per
individual decreases with
increasing group size
Resources determine type of competition Contest
- Food is found in defensible
clumps
– Individuals compete
aggressively over access to
resources
Dispersal in primates: Baboon-macaque-guenon group* Male dispersal is the norm
- Male dispersal is the norm
Dispersal in primates: Colobines, lemurs, apes, New World monkeys
- Female dispersal and
bisexual dispersal common
Why do animals disperse?
- Avoid inbreeding
– reason in many cases for
natal dispersal - Seeking better resources
- Result of intrasexual
competition
– but does not explain
species where individuals
leave voluntarily
Solitary
Males defend home ranges that encompass home ranges of several females
Monogamous Pairs
When females are dispersed, males may associate permanently with one of them
Polyandry
Several males associate with one reproductive female
Polygyny: One-male (‘harems’)
If females are clumped in groups, one male may be able to monopolize access
to a group
Male infanticide in Primates
- Infanticide by males is
major source of infant
mortality in primates
– especially in single-male
groups - Most cases of infanticide
follow changes in male
residence (eg. takeovers)
or dominance rank
Polygyny: Multimale (mating system:
Polygynandry/promiscuity)
Females clumped in groups, and multiple males associate with them
Human mating
system
- Majority of human societies allow polygyny
- but its frequency depends on subsistence
style:
– monogamy predominates in forager societies
– pastoralists and agriculturalists show significant
polygyny
Anatomical evidence:
Sexual dimorphism (SD)
- Correlation between sexual
size dimorphism and
polygyny in many mammalian
groups - Pronounced body size
dimorphism is suggestive of
high levels of male–male
competition
Testis size &
mating system
- Primate species in
promiscuous mating systems
have much larger testes
relative to body size than
primates in single-male
groups (monogamous +
polygynous) - Humans: mild level of
promiscuity
