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18 Cards in this Set
- Front
- Back
What does Life History theory seek to do?
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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 |
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Two main kinds of tactic (Jones 2011)
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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 |
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Two main kinds of tactic (Jones 2011)
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2. K selected. The second group, which primates belong to, is characterized by long lives, modest reproductive rates, and extensive parental care.
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How are primates different?
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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. |
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What is the reason for primates' more intense manifestation of these life history traits?
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- 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. |
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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 |
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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
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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 |
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Expensive Tissue Hypothesis
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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 |
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Primate Adaptations
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An adaptive trait is one which enhances fitness
It is favoured by selection |
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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 |
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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.) |
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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 |