Transcript Ch. 53 - Crestwood Local Schools

Population Ecology
Study
of the factors that
affect population size and
composition.
Population
Individuals
of
a single
species that
occupy the
same area.
Important
Characteristics
1. Density
2. Dispersion
Density
Number
of individuals per
unit area or volume.
Ex:
- 5 million/m3
Trees - 5,000/km2
Deer - 4/km2
Diatoms
Dispersion
Pattern
of spacing among
individuals.
Types:
1. Clumped
2. Uniform
3. Random
Clumped Dispersion
May
result form a patchy
environment.
May increase chances for
survival.
Ex:
Schooling
behavior
Flocks of birds
Uniform Dispersion
Often
the result of antagonistic
interactions between
individuals.
Ex:
Territories
Spacing
between desert plants
Random Dispersion
Often
the result of the
absence of strong attractions
or repulsions between
individuals.
Not a common pattern.
Demography
The
study of the vital
statistics that affect
population size.
Ex: Birth and Death rates
Demographic Factors
Age
structure of the
population.
Birth and Death rates.
Generation time.
Sex ratio and reproductive
behavior.
Life Tables
Mortality
summary for a
cohort of individuals.
First developed from life
insurance studies.
Life Tables Show
Mortality
rate per year.
Life span of the organism.
Fecundity (birth rate).
Survivorship Curve
Plot
of the numbers of a
cohort still alive over time.
Curve Types:
Type
I
Type II
Type III
Type I
Low
early deaths.
High late deaths.
Ex:
Humans
Other
large mammals
Type II
Constant
death rate.
Ex:
Annual
plants
Many invertebrates
Type III
High
early deaths.
Low late deaths.
Ex:
Trees
Oysters
Comment
Curve
type may change
between young and adults.
Ex: Nestlings - Type III
Adult Birds- Type II
Life History Strategies
1. "r" or Opportunistic species
2. "k" or Equilibrial species
"r" Species
Increase
fitness by producing
as many offspring as
possible.
Do this by:
Early
maturation
Many reproductive events
Many offspring
Result
Maximize
reproduction so
that at least a few offspring
survive to the next
generation.
Most offspring die
(Type III curve).
"k" Species
Increase
fitness by having
most offspring survive.
Do this by:
High
parental care
Late maturation
Few reproduction events
Few offspring.
Result
Maximize
survivorship of
each offspring.
Few offspring, but most
survive (Type I curve).
What is the strategy
For
a weed?
For an endangered species?
For Garden Pests?
Population Growth
DN/Dt
=b-d
Where:
N=
population size
t = time
b = birth rate
d = death rate
Rate of Increase
r
= difference between birth
rate and death rate.
r = b - d
Equation:
DN/Dt
= rN
N = population size
t = time
r = rate of increase
From Calculus
The
equation
DN/Dt = rN
becomes:
dN/dt = rmax N
rmax = intrinsic rate of increase
Exponential Growth
dN/dt
= rmax N
Characteristic of "r" species.
Produces a “J-shaped”
growth curve.
Only holds for ideal
conditions and unlimited
resources.
Logistic Growth
dN/dt
= rmax N K-N
K
K = carrying capacity
Result
“S-shaped”
growth curve.
Characteristic of “k" species.
Common when resources are
limited.
Comment
K
is not a constant value.
Populations often oscillate
around “K” as the
environment changes.
Additional Comments
Populations
often overshoot
“K”, then drop back to or
below “K”.
AP Exam rarely asks you to
work the equations, but you
should be able to give them.
Regulation of
Population Size
1. Density- Dependent Factors
2. Density- Independent Factors
Density-Dependent
Affect
is related to N.
As N increases, mortality
increases.
Ex: Food, nesting space,
disease
Density-Independent
Affect
is not related to N.
Mortality not related to
population size.
Ex: Weather and climate
Population Cycles
Cyclic
changes in N over
time.
Often seen in predator/prey
cycles.
Ex: Snowshoe Hare - Lynx
Causes
Density
dependent factors.
Chemical cycles.
Saturation strategy to
confuse predators.
Age Structure
Diagrams
Show
the percent of a
population in different age
categories .
Method to get data similar to
a Life Table, but at one point
in time.
Importances
Can
be used to predict future
population growth trends,
especially for long lived
species.
Exponential Growth
Produces
age structures that
are a triangle or pyramid
shape.
Logistic Growth
Produces
age structures that
have even sizes between
most age categories.
Declining Populations
Produce
age structures with
a narrow base and wider
middles.
Summary
Know
density and dispersion
patterns.
Know Life Tables and
survivorship curves.
Be able to contrast and
compare “r” and “k”
strategies.
Summary
Know
exponential and
logistic growth curves and
equations.
Know density and densityindependent growth factors.