Primate Biology Ii

Front 1

What does Life History theory seek to do?

Back 1

Life-history theory seeks to explain;

- the diversity of tactics through which different organisms achieve evolutionary persistence and increase

- why the tempo and mode of reproduction can vary so much across taxa

Front 2

Two main kinds of tactic (Jones 2011)

Back 2

1. r selected (r like rodents). An organism lives for a short time and breeds extensively, producing an abundance of low-quality offspring (rodents)

The chance of offspring survival is low, but there are enough offspring that at least two should survive

Front 3

Two main kinds of tactic (Jones 2011)

Back 3

2. K selected. The second group, which primates belong to, is characterized by long lives, modest reproductive rates, and extensive parental care.

Front 4

How are primates different?

Back 4

These traits are more intense in primates than in any other mammal. Together, these traits define a life-history of reduced reproductive effort.
- late age of first reproduction
- long lives
- low fertility

Because of their unusual constellation of life-history traits, primates play an important role in the continued development of life history theory.

Front 5

What is the reason for primates' more intense manifestation of these life history traits?

Back 5

- Primates like highly variable foods

The tendency for primates to specialize in high-quality, high-variability food items may make them particularly susceptible to environmental variability and explain their low reproductive-effort tactics.

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Example

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Gorillas eat a folivorious diet of leaves. Leaves are a constant unvarying food source. Gorillas have about one child every four years

Orangutans eat a frugivorous diet of fruits. Fruits are highly variable throughout the year. Orangs only have one child every eight years.

Orang's slow growth and weaning could be to spread the risks associated with a variable diet.

Front 7

Example (cont.)

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Longer generation times mean that individuals sample a longer range of temporal environments with their reproductive events

Orangs have the lowest reproductive success of any mammal

Front 8

Therefore primate life histories are adapted to...

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environments and ecological conditions with high variability

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The brain is a large and expensive organ to grow

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Primates have very large brains

Front 10

Ecological theory for brains

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- Fruit is seasonal and therefore highly variable
- It takes a larger brain to overcome the challenge of how and where to find fruit
- Does fruit provide the extra energy needed to fuel the brain?
- Frugivores do have a larger brain/body ratio than folivores

Front 11

Expensive Tissue Hypothesis

Back 11

Aieolli and Wheeler (1995)
The expensive-tissue hypothesis suggests that the metabolic requirements of relatively large brains are offset by a corresponding reduction of the gut

Front 12

Primate Adaptations

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An adaptive trait is one which enhances fitness
It is favoured by selection

Front 13

How are primates generalized?

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Primates have a generalized body plan, which means they lack specialiations such as a giraffes neck
- This makes them versatile
- Primates have a wide variety of modes of travel

Front 14

All primates have... 1.

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1. Grasping hands with opposable thumbs and big toes (this is a fundamental primate adaptation, although some prosimians don’t fully exhibit this trait)

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All primates have... 2.

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2. Flattened nails instead of claws (apart from marmosets and tamarins)

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All primates have... 3.

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3. Forward-facing eyes with stereoscopic vision
Eyes mounted on the front of our heads
This gives excellent depth and perception
Overlapping fields of vision give us a 3d view of the world

(explained by Arboreal Hypothesis, Visual Predetation hypothesis and Angiosperm rad. hyp.)

Front 17

All primates have... 4.

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4. Generalized teeth
Allowing us to eat lots of types of food

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All primates have... 5.

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5. Large brains for body weight

Explained by Dunbar 1998 Social Brain Hypothesis
Aiello and Wheeler 1994 Expensive tissue hypothesis