Primates
What is a Primate
Class: Mammalia
Order: Primate
Divided two groups
Strepsirrhines - Wet-nosed primates
Haplorrhines - Dry nose primates
Primates are Generalized
Generalized: traits are adapted for many functions
Retained several ancestral mammalian traits
e.g., number of digits = 5 (polydactyl)
Primate Characteristics
Generalized Skeletal Structure
Grasping hands or feet
Pentadactylism (5 digits)
Tendency toward upright posture
Flexible joints
Enhanced Touch
Tactile pads or dermal ridges
Nails instead of claws
Opposable digits'
Coloured Vision
Forward-facing eyes (binocular vision)
Colour vision (some species)
Protected eye sockets (postorbital bar or fully enclosed orbits)
Reduced Smell and Hearing
Smaller olfactory bulb in the brain
Smaller immobile ears (not strepsirrhines)
Dietary Versatility
Fewer teeth
Generalized
Dentition
Eat most things
Insectivore
Gunnivore
Folivore
Frugivore
Omnivore
Faunivore
And more
Other Primate Characteristics
Petrosal Bulla
Increased encephalization (brain size)
Extreme 'k' selection (fewer offspring)
Prolonged infant dependency and increased learning and socialization
Transfer of learned behaviours
Complex social groups
Complex forms of communication
Why did primates evolve their particular set of traits?
5 Hypotheses (Silcox et al., 2015)
The Arboreal Hypothesis
The primate pattern represents an adaptation to an arboreal habitat or to life in trees
Complex 3-D environment with high risks
Grasping hands, stereoscopic vision are assets
Objections to arboreal hypothesis
Other orders have arboreal species that do not share primate pattern (i.e. opossums)
Visual Predation Hypothesis
The primate pattern represents an adaptation to foraging for insects in the terminal branches of trees
Objections
Other arboreal insect eating mammals with visual specialization?
Evidence of primitive condition of omnivorous diet
Other modes of detection
Angiosperm Diversification or Angiosperm Coevolution Hypothesis
Primates co-evolved with flowering plants
Angiosperms (flowering plants) existed way after the dinosaurs (~30 million years before first primates
Adaptive Diversification
Refers to the evolutionary process by which a species diversifies to occupy different
the splitting of an ancestral lineage into two derived groups due to frequency-dependent ecological interactions
Objections
Angiosperms first appear in the fossil record millions of years before the first primates
Early primates were not nectar specialists
Early marsupials had grasping hands before the evolution of flowering plants
Terminal Branch Feeding/Visual Predation
Primate pattern better explained only in terms by
Objections
Surprisingly few
Grasping Leaping Hypothesis
Primate ancestors were arboreal
Rapidly jumped and secured themselves in arboreal environment
Visual ability to judge distance when leaping
Herbivory first - then grasping leaping
Objections
Less susceptible to criticism
Fossil first approach
Which is the most likely hypothesis?
Ancestors to primates were already arboreal
Grasping didn't evolve a s a suite of characters
2 stage process
Primates lack features associated with specialized leaping
Earliest primates don’t have teeth specialized for eating insects
No connection between orbital characteristics and feeding on insects
What's left?
Angiosperm diversification hypothesis was most likely!
Two More Hypotheses
Snake detection hypothesis
Fear specifically of snakes may have pushed evolutionary changes in the primate visual system allowing pre-attentional visual detection of fearful stimuli.
Narrow Niche Hypothesis
Suggests that the primate morphological suite evolved not only from selection pressure for fine branch use, but also from a lack of engagement in other activities
Where do Primates Live?
Mainly the tropics
Except… China, Japan, Northern Africa
Some are arboreal and some terrestrial
How Doe Primates Move?
Locomotion:
Quadrupedal: walking on all four limbs
Vertical Clinging and Leaping (VCL)
Brachiation: arm swinging
Bipedal?: habitually, just humans
What is Behaviour
Behaviour = anything organisms do that involves an action in response to an internal or external stimuli
Innate or learned behaviour
Tinbergens 4 questions
Different levels of explanation
Ultimate
Function
Phylogeny
Proximate
Mechanism (causation)
Ontogenetic
Primate Field Studies
Early primatology rooted in anthropocentric interests in primates
The "tri-mates"
Early descriptive reports
Habituation
Animal is habituated when it stops altering its behaviour in the presence of humans
Behavioural Sampling Techniques/Methods
Ad-libitum
When you record everything you see
Instantaneous scan sampling
Write down observed behaviour at set time intervals
Focal Animal Sampling
Write down observed behaviour continuously for predetermined amount of time
All-occurrences sampling
The researcher selects one or a few specific behavioural events and records every occurrence of that (those) behaviour(s) within an animal group
The Evolution of Behaviour
Behavioural ecology
Study of the evolution of behaviour, emphasizing the role of ecological factors
Behaviours evolved through natural selection
Including social behaviour
Primate Social Structure
Primate groups:
Size
Composition
Socioeconomic sex ratio
Operational sex ratio
Degree of cohesion
Primate Group Types
Single female and her offspring
Monogamous family group
Polyandrous
Polygynous
Uni-male, multi-female
Multi male, multi female
Fission fusion
Factors Influencing Social Structure and Behaviour
Food
Diet
Different species focus on different food types
Resource distribution
Leaves more widely distributed and abundant
Insects patchy
Fruits can be clumped
Home Range
The total area exploited by an animal or social group
Usually given for 1 year - or for the entire lifetime - of an animal
Relationships with other species
Predation
Primates vulnerable to different types of predators
Predation is difficult to study
Have developed anti-predator strategies
Sympatric species
Can be a type of anti-predator strategy
e.g., red colobus monkeys and diana monkeys
Dispersal Patterns
One sex leaves natal group
Reduce competition for mates, reduce inbreeding
Individuals who stay in natal group = philopatric
Other influences
Activity patterns
Diurnal, nocturnal, cathemeral
Most primates diurnal but evolved from nocturnal ancestor
Human activities
Hunting
Habitat clearing
Communication
Any act that conveys information to another individual
Autonomic
e.g. body language
Intentional
e.g. grooming, gestures, vocalizations
Stages of Communication
Signal
e.g. chimpanzee facial expressions, displays
Motivation
Internal state, inferred from behaviours before and after
Meaning
Depends on individuals involved and context
Function
Tactile Communication
Primates are physical creatures
Play
Grooming
Avoid conflict
Visual Communication
Body posture
Facial signalling
Deception
Olfactory Communication
Less acute in primates
Passive or deliberate
Vocal Communications
Distinguish between species
Distinguish between groups
Alarm calls
Spacing
Communication
Evolution of communication
Ritualized behaviours
e.g., crouching
Communication helps make social living possible
Aggression and Affiliation
Affiliative: amicable association between individuals
e.g. grooming
Maintains social bonds
Reconciliation
Displayed through grooming
Aggression: conflict between individuals
e.g. fighting, displays
Why aggression?
Dominance
Access to resources
Ultimately to reproduce
Reproductive Strategies
Reproduction = driving force of life
Estrus = female is sexually receptive/fertile
Physical or behavioural indications
Female strategies
Reproductive success limited by resources
Maximize access to food
Male strategies
Little investment
Maximize access to mates
Sexual Selection
Type of natural selection that operates on only one sex within a species
Usually expressed in sexual dimorphism
e.g., body size, colouration, canines
Infanticide
Killing of infants by primate males
Male reproductive strategy
Reduces competitors
Increases reproductive success
Sexual selection infanticide hypothesis
Infanticidal males should not kill own offspring
Climate
Seasonality:
Rain, temp
Zone:
Tropical: equator north to tropic of cancer, south of Tropic of Capricorn
Sub-Tropical: tropics to 40 degrees latitude north and south
Habitat
Forests
Grasslands
What is Food for Primates
Fruit
Leaves
Flowers
Primate Diets
Many different
Diet and Body Size
Small = High BMR
Large = Low BMR
Why?
Allometry: surface area to volume ratio
Sex Differences in Diets
May differ because of access to resources
High vs Low Quality Diets
High: rich in easily digestible energy and protein; growth diets; e.g. fruits, seeds
Low: poor in energy and protein; subsistence diets; e.g. mature leaves
Attractiveness of Plants
Can either be made attractive or unattractive
Done to protect itself or to make it more available to get eaten
Toxins/Alkaloids and tannins make a plant unattractive
To address this, some primates have adaptations to chemical deterrents
Other Plant Strategies
Produce "en masse" or mass fruiting
Foraging Strategies
Benefits: energy/nutrients obtained from food
Costs: time and energy expended to locate, eat, defend, and digest food
Activity budget: time spent in various activities
How do Primates Cope?
Foraging Strategies:
Food selection
Size of fruit patch
Temporal availability of food resources
Change diet
Change ranging patterns
Spatial distribution of food patches
Home range and daily moments
Grouping patterns
Fallback Foods
Foods that aren't meant for growth, not nutrient-rich, but primates evolved to eat
Predation
All primates are predatora
Predation is a major factor in primate evolution
Impetus for group living?
Primate Responses to Predation Pressure
Alarm calling
Aggression
Concealment
Grouping (herding)
Philopatry