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Chapter 11

BIOLOGY 2F03 Chapter Notes - Chapter 11: Adolph Murie, Survivorship Curve, Life Table

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D R.Kajura

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Chapter 11 – Population Structure
Population structure: defined by a number of factors. Ex: patterns of mortality, age
distributions, sex ratios and dispersal.
Adolph Murie: foundational figure in population ecology
- Observations of interactions between wolves and sheep
- Should wolf population be cut down because they kill too many sheep?
oFollowed the hunting patterns of wolves  they left the skulls of the
sheep behind which could be used to get age and sex of sheep
oMost of the sheep attacked were very young or very old
11.1: Patterns of Survival
Survivorship Curve: summarizes patterns of survival in a population
Life tables: list the births, survivorship, and deaths (mortality) in populations
Estimating Patterns of Survival
3 main ways to estimate patterns of survival:
1. Cohort Life Table: identify large number of individuals (a cohort) that are
born at about the same time and keep records on them from birth to death
a. Hard to keep track of a cohort
2. Static Life Table: go in the field for narrow window of time & record age at
death of large number of individuals (born at different times)
a. Accuracy can be difficult  hard to estimate age of death
3. Age Distribution: the proportion of individuals of different ages within a
a. Used to estimate survival by calculating the difference in proportion
of individuals in succeeding age classes
b. Produces a static life table  assumes that the difference in numbers
of individuals in one age class & the next is result of mortality
c. Assumptions: population is neither growing nor declining, & not
receiving or losing members.
High Survival Among Young Individuals
Survivorship curve: shows patterns of life and death within a population
- Tell us if mortality rates for a given population change with age (linear vs
- Y-axis: age (logarithmic scale)
Sheep studied by Murie & other large vertebrates: high rates of survival among
young & middle-aged and high rates of mortality among older members
- Seen in some plants and smaller vertebrates as well
Constant Rates of Survival
Straight lines on survivorship curve
- Die at the same rate throughout life
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