Studying Life History

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Studying Life History
Populations In Evolution
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Lecture Goals

• Introduce the concepts and terms of life history
  theory
• The Logistic perspective r K continuum
• Adding other dimensions
• Explicit age structured approaches
• The Lotka-Euler equation
• Predicting age at maturity

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Natural History - everything about an organism,
its forms, activities, interactions with other
individuals, species, and environment. -
observations not hypothesis tests - lacks
theoretical framework - post-hoc
explanations - more qualitative than
quantitative - but it is the data that we
work with - and great PBS material as well
It is what hooks us initially, but as we advance
in the field we must put these observations into
predictive, testable, theoretical frameworks.
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A Natural History Example The Albatross
May be at sea for months (up to a month with
chick)

• Matures around 8 years
• Breeds on islands (no pred.)
• Doesnt breed each year

• Only lays one egg
• May raise up to 21 chicks
• Very long lived

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A Natural History Example The Bobwhite Quail

• Can live 5-6 years
• But low survival
• Most live less than 1 year
• Predators include everything
• Snakes, raccoons, owls,armadillos, possums, ...
• Prefer disturbed habitat
• Stay within lt 50 hectares

• Nest as pair in spring
• will renest easily
• Clutch 12 25 eggs
• Mature in 1st year
• Form covey in fall
• over winter
• group defense

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To persist through millennia, an organism has to
replace itself, on average, through its lifetime

• Why such different life styles?
• 1 egg or gt20 eggs?
• Nest every chance or once every few years?

• Ultimately, our hypotheses are based upon
  quantifiable traits related to fitness

Environment gtgtgt Selection gtgtgt Evolution
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Life History, What is it?
Aspects of the natural history of an organism
that are related directly to survival and
reproduction.
Timing is everything
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Some Terms of Life History

• semelparous - reproduce once, then die
• iteroparous - reproduce many times
• precocial - offspring highly developed at
  birth (ready to fend for themselves)
• altricial - offspring with low development at
  birth (need much parental care)
• senescence - the increase in mortality with age
  that can be attributed to changes in
  the organism

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Tradeoffs In Life Histories
Ultimately, the uber-critter will

• Potentially live forever
• Breed continuously
• Produce large broods
• Produce offspring full grown and mature
• Be too big/fast/??? for predators to catch

But there are limited resources available!
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Should I breed or should I grow A clash of
objectives .
Maintenance
Food
Reproduction
Storage Growth
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Evidence of Tradeoffs in Beech Trees
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Annual growth
1
Year

• Beech trees mast producing large quantities of
  seeds in some years
• Overwhelm seed predators
• Reduces resources for growth

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Evidence of Tradeoffs in Placental Mammals

• longer parental care lower fecundity
• after correcting for body size
• relative fecundity relative investment