Lab 7 introduction

BIOL205
Ecology Lab 7
Analysis of population
(age structure and rates of population
change)
Dr. Erik D. Davenport

Introduction of this lab exercise
 This lab exercise is corresponding to the
lecture 10 – population dynamics.
 Since lecture 10 (population dynamics)
includes some difficult concepts and
equations, we will first go through a detailed
review of these concepts.

Concepts in population dynamics
 Life table (we will only talk about cohort life table)
 survivorship curve
 age distribution
 Birth rate
 fecundity schedule
– net reproductive rate (R0)
– per capita rate of increase (r)
– generation time (T).

Life table
 life table lists both the survival and the death
(or mortality) in the population to describe the
survival pattern.
 The cohort life table lists the survival and the
death a group a individuals that were born at
the same time.

Survival Death
Do you need both survival
And death columns???

survivorship curve
 A survivorship curve summarizes (visualize) the
pattern of survival (and death) in a population.
 Survivorship curve represents the same thing as a
life table, it is just a visualization of a life table.
 You need the information in life table to draw
survivorship curve!!!!

7Be careful the Y-axis of the curve, it is in log scale!!!!

Survivorship Curves
 Type I: Majority of mortality occurs among
older individuals.
– Dall Sheep
 Type II: Constant rate of survival throughout
lifetime.
– American Robins
 Type III: High mortality among young,
followed by high survivorship.
– Sea Turtles
8

Age Distribution (structure)
 Age distribution (structure) of a population
gives the information such as how many of
the individuals are young, how many are
old…
 It reflects its history of survival, reproduction,
and growth potential.

Don’t get confused for age distribution
and survivorship curve!!!!

The difference!!!
 Survivorship curve is from life table, all individuals
are born at the same time. As the time pass by, the
number of individuals decreases because of death.
 Age distribution (structure) is a snapshot of the age
information of the current population – how many are
young, how many in mid age, and how many are old.
 So they represent totally different information!!!!
 Age distribution reflects its history of survival,
reproduction, and growth potential

 Miller published data on age distribution of
white oak (Quercus alba).
– Age distribution biased towards young trees.
– Sufficient reproduction for replacement.
– Stable or growing population

Age Distribution
 Rio Grande Cottonwood populations
(Populus deltoides wislizenii) are declining.
– Old trees not being replaced.

age population
Under 5 years 353,393
5 to 9 years 391,318
10 to 14 years 392,135
15 to 19 years 356,119
20 to 24 years 314,129
25 to 34 years 748,521
35 to 44 years 916,156
45 to 54 years 755,032
55 to 59 years 268,647
60 to 64 years 201,729
65 to 74 years 321,285
75 to 84 years 211,120
85 years and over 66,902
What kind of conclusion you will get from this age distribution?
Would you say the populations are stable, declining or dynamic?
Explain the reason.
(You should give a reasonable and detailed explanation).

Rates of Population Change
 Birth Rate: Number of young born per
female.
 Fecundity Schedule it is a table that lists the
birth rates for females of different ages.
 So, both life table and Fecundity schedule
are tables!!!
 Any same column for fecundity schedule and
life table?
21

 life table lists the survival (and death) of a population
at different ages.
 Fecundity schedule lists the birth at different age.
 The age column is in both the life table and fecundity
schedule!!!
 Life table combines with a fecundity schedule can be
used to estimate some important parameters about
population dynamics: net reproductive rate (R0) and
per capita rate of increase (r), and generation time
(T).

– Ro = Net reproductive rate: Average number of
offspring produced by a female in a population during
its lifetime.
Ro=∑lxmx
– X= Age interval.
– lx = % pop. surviving to each age (x).
– mx= Average number seeds produced by each
individual in each age category.

Generation time (T): average lifespan for
individual in a population.
T = ∑ xlxmx / Ro
Per Capita Rate of Increase (r): normalized
population growth rate
r = ln Ro / T
– ln = Base natural logarithms

How get this column??
Survival, from life table Brith, from fecundity schedule

Lab 7 introduction

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Lab 7 introduction