Transcript Chapter 10 Stuff

Chapter 10 (Brief Overview)
But first, review…
• Resource Utilization Curve
• How is it related to the niche?
– Niche discussion…
Joseph Grinnell
Charles Elton
GE Hutchinson
• How is it related to acclimation?
– Not a constant set of environmental conditions
• Questions about this stuff?
What is life history?
• The life history is the schedule of an organism’s
life, including:
– age at maturity
– number of reproductive events
– allocation of energy to reproduction
– number and size of offspring
– life span
Compare
• Elephant
– Life span: >50y
– Age at 1st reproduction: 1320yrs
– Gestation: 21-22m
– # young: 1
– Parental care:
• ♂ - none
• ♀ - herd consists of
matriarch, male and
female offspring until
>12y, then male offspring
leave herd, female
offspring stay.
• Salmon
– Life span: 1-8y
– Age at 1st reproduction:
• 1-8y
– Gestation: how long it
takes to swim from ocean
to spawning grounds
– # young (eggs):
• 2500 - 7000
– Parental care:
• ♂ - none
• ♀ - none
Survivorship curves
What influences life histories?
• Life histories are influenced by:
– body plan and life style of the organism
– evolutionary responses to many factors,
including:
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•
•
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physical conditions
food supply
predators
other biotic factors, such as competition
A Classic Study
• David Lack of Oxford
University first placed life
histories in an evolutionary
context:
Snow bunting
– tropical songbirds lay fewer eggs per
clutch than temperate counterparts
– Lack speculated that this difference was
based on different abilities to find food for
the chicks:
• Temperate breeders have longer days in
which to find food than tropical breeders
Red-headed manakin
Lack’s Proposal
•
Lack made 3 key points:
1. because life history traits (i.e. # of eggs/clutch)
contribute to reproductive success they influence
evolutionary fitness
2. life histories vary in a consistent way with respect to
factors in the environment (reaction norms)
3. hypotheses about life histories are subject to
experimental tests
–
Therefore: Life history is shaped by natural selection
and are amenable to scientific method
An Experimental Test
• Lack:
– Artificially increase # of eggs/clutch.
– There would be no reduction in success.
– Therefore, the number of offspring is limited by
food supply
• This proposal has been tested repeatedly:
– Gören Hogstedt (1980) manipulated clutch
size of European magpies:
• maximum number of chicks fledged
corresponded to normal clutch size of seven
• Hogstedt (1980) – Magpies (Pica pica)
• Perrins and Moss (1975) – Great tits (Parus major)
Recapture probability
Expected w/
No resource limitations
Predicted by Lack
Observed
2
8
Brood Size
14
Components of Fitness
• Generic: # offspring in next and future gens.
• Genetic: proportion of alleles in next and future gens.
• Fitness, ultimately dependent on producing successful
offspring
• Components:
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–
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maturity (age at first reproduction)
parity (number of reproductive episodes)
fecundity (number of offspring per reproductive episode)
aging (total length of life)
Life Histories: A Case of
Trade-Offs
• Organisms face a problem of allocation of
scarce resources (time, energy, materials):
– the trade-off: resources used for one function
cannot be used for another function
• Remember:
– Altering resource allocation affects fitness.
• Consider the possibility that an oak tree might
somehow produce more seed:
– how does this change affect survival of seedlings?
– how does this change affect survival of the adult?
– how does this change affect future reproduction?
Concept of renewal
principal
n = years
FV = P(1 + r)n
Future Value
r - Interest rate
Now = P
Year 1 = P(1+r)
Year 2 = P(1+r)2
Year 3 = P(1+r)3
Choices…
Self survival?
Parental care?
Few large?
Many small?
How fast growth and maturity?
How often do I breed?
Life histories resolve conflicting
demands.
• Life histories represent trade-offs among
competing functions:
– a typical trade-off involves the competing demands of
adult survival and allocation of resources to
reproduction:
• kestrels with artificially reduced or enlarged broods exhibited
enhanced or diminished adult survival, respectively
• Hence: parental cost.
The life table…