Download Population Ecology

Population Ecology: Population
Growth
Chapter 52
p. 1136-1158
Populations

A population is a
group of
individuals of the
same species that
live in the same
area
Population Ecology: Vocabulary

Density:

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
The number of individuals per unit
area/volume
Example: 47 elephants/km2
Dispersion:

The pattern of spacing among
individuals in a population
Clumped
 Uniform
 Random

Uniform


Environmental
conditions are
uniform
Causes
COMPETITION or
antagonism
between
organisms
Clumping

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Most common
Reproductive
patterns favor
clumping
Social behaviors
lead to clumping
Optimal density is
usually
intermediate
(medium)
Random

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
No competition
No tendency to
group/clump
Conditions are
uniform
Rarely happens!
Factors That Influence Population Size

There are 3 major factors that influence
population size:
1. the number of births
2. the number of deaths
3. the number of individuals that enter or
leave a population
- Immigration:
individuals entering an existing population
- Emigration:
individuals leaving an existing population
Life Histories

Clutch size: Number of offspring produced at each
reproductive episode

Semelparity

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
Most energy spent in growth and development
One large reproductive effort, and then die
Used when survival rate is low, or environment
unpredictable
Many insects, annual plants, salmon, etc.
Iteroparity

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Produce fewer offspring at a time over a span of
many seasons
Used when environment is stable but need to
compete
Humans, panda bears, etc.
Estimating Population Size

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The mark-recapture method can be
used to estimate the size of a
population
Capture, mark, release
Recapture and count
Equation:
N = Number marked x Total catch 2nd time
Number of marked recaptures
Patterns of Population Growth

Exponential Growth:
 Occurs in ideal
conditions with
unlimited resources
 J shaped curve
 Book example:
 1 bacterium
(reproducing every
20 minutes) could
produce enough
bacteria to form a 1foot layer over the
entire surface of the
Earth in a day
Patterns of Population Growth


Exponential growth
cannot continue
indefinitely
It is characteristic of
populations who are
entering a new
environment OR
those whose
numbers are
rebounding from a
catastrophic events
Patterns of Population Growth

Logistic Growth:
 Takes into account
the effect of
population density
on population growth
 Occurs when
resources become
more scarce
 Characterized by an
S-shaped curve
Patterns of Population Growth

Carrying capacity (K):




The maximum number of individuals that a
particular environment can support over a long
period of time
Determined by such limiting factors as crowding
and food resources
Graph levels off at carrying capacity
K-selected populations (equilibrial
populations) live near or at the carrying
capacity
K-strategists



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



Density stays near carrying
capacity.
Large, slow growing organisms
Small population sizes
Long life span; slow maturation
Few young/small clutch size
Reproduce late in life
Parental care
Most large mammals; endangered
species
r- strategists (reproduction)

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
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Grow exponentially when environmental
conditions allow; when conditions
worsen, population size plummets.
Short life span
Reproduce early in life
Many offspring/large clutch size
Usually small in size
Little or no parental care
Bacteria, some plants, insects
Population Ecology: Limits on
Population Size
Chapter 52
p. 1136-1158
Limiting Factors
 There
are a number of factors
that limit the size of
populations:
Density-dependent limiting
factors
 Density-independent limiting
factors

Density-Dependent Limiting Factors
 Effect
intensifies as
the population
increases

Intraspecific
competition
 Food,
space, etc.
Predation
 Disease (if caused by
pathogen/contagious)

Boom-and-Bust Cycles
Density-Independent Limiting Factors

Unrelated to population size



Climate
Disease (if not caused by pathogen/not
contagious)
Pollution
The Interaction of Limiting Factors
 Density-dependent
and densityindependent limiting factors
often work together to regulate
the size of a population

Deer in snowy winter
 Starve
from lack of food (DDLF)
 Severity of winter/depth of snow
determines access to food (DILF)
Survivorship Curves



Type I- live to old age
& die (most large
mammals)
Type II- constant
mortality rate (rodents,
lizards, hydra)
Type III- high
mortality at young age,
but if they survive they
live a long life.
Age-Structure Diagrams
Human Population Growth
Human Population Growth


The human population has been
increasing exponentially since
approximately 1650
http://www.pbs.org/wgbh/nova/wor
ldbalance/numbers.html
Human Population Growth

Implications of exponential human
population growth:



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Lack
Lack
Lack
Lack
of
of
of
of
food supplies
space
natural resources (metals, fossil fuels, etc)
sites for waste disposal
Ecologists cannot agree on a carrying
capacity for Earth


Are we going to reach carrying capacity
through individual choices and/or government
programs?
OR
Is Earth’s population going to “level off” as a
result of mass deaths?