Population Ecology
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Transcript 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:
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
Most common
Reproductive
patterns favor
clumping
Social behaviors
lead to clumping
Optimal density is
usually
intermediate
(medium)
Random
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
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
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
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
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)
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:
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?