Chap 43.Populations.part 1

Chapter 43
Populations and
Exponential Population
Growth
 Population
– Group of individuals of a single
species living in the same
general area
Population
ecology
studies:
–Density
–Distribution
–Age structure
–Variations in population
size
 Population
density
–#of individuals per unit area or
volume
 Population
size
–Total # of individuals in a population
–This is usually estimated using
density and distribution
Life Tables
Survivorship Curves
 graphic
way of representing the data
in a life table
Number of survivors (log scale)
1000
100
Females
10
Males
1
0
2
4
6
Age (years)
8
10
Survivorship Curves
the survivorship curves for:
– Oysters
– Squirrels
– Humans
% of Survivors
 Predict
% of maximum life span
Survivorship Curves
Three types:Type I, Type II, and Type III
1,000
I
Number of survivors (log scale)

100
II
10
III
1
0
50
Percentage of maximum life span
100
Reproductive Table
REPRODUCTIVE STRATEGIES
 semelparous
species
– “big-bang” reproduction
– Reproduce a single time and die
– Must be synchronized (do you know
why?)
Figure 52.6
 Iteroparous
species
– produce offspring repeatedly over time
Why?
 Likely
explanation is that
semelparous species have a high
adult mortality.
 It’s better to put all of one’s
reproductive effort in early, while still
alive.
Parents surviving the following winter (%)
“Trade-offs” and Life Histories
100
Male
Female
80
60
40
20
0
Reduced
brood size
Normal
brood size
Enlarged
brood size
“Trade-offs” and Life Histories
Strategy #1:
 Many, small
seeds
What are the
“trade-offs”?
(a) Most weedy plants, such as this dandelion, grow quickly and produce a
large number of seeds, ensuring that at least some
will grow into plants and eventually produce seeds themselves.
Figure 52.8a
“Trade-offs” and Life Histories
Strategy #2:
 Few, large
seeds
What are the
“trade-offs”?
(b) Some plants, such as this coconut palm, produce a moderate
number of very large seeds. The large endosperm provides
nutrients for the embryo, an adaptation that helps ensure the
success of a relatively large fraction of offspring.
Figure 52.8b
POPULATION GROWTH
Population Growth
 Population
growth (ignores
immigration and emigration)
dN 
dt # births - # deaths
Population Growth
Zero population
growth
population growth curve
30
25
B=D
N
20
15
N
10
5
0
1
2
3
4
time
5
6
7
Exponential population growth

Occurs under ideal conditions
 Under
these conditions the rate of
reproduction is at its maximum
(rmax)
Exponential Growth
Equation: Nt+1 = Nt + rmaxNt
N = population size
t = generation
rmax = max reproductive rate
Exponential Growth
Exponential population growth
 J-shaped curve
2,000
r=1
r = 0.5
Population size (N)
1,500
1,000
500
0
0
10
5
Number of generations
15
Exponential Growth
Characteristic of rebounding populations
8,000
Elephant population

6,000
4,000
2,000
0
1900
1920
1940
Year
1960
1980
END OF PART 1

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