Download Ecology of Populations

Ecology of Populations
Scope of Ecology


Ecology – what is it?
Definitions:
 Habitat - Place where an organism lives.
 Population - All the organisms within an
area belonging to the same species.
 Community - All various populations
interacting at same locale.
 Ecosystem – A collection of communities
Ecological Levels
Density and Distribution
of Populations
 Population
Density - Number of
individuals per unit area or
volume.
 Population Distribution - Pattern
of dispersal of individuals within
the area of interest.
Uniform Distribution
Uniform. Birds nesting on small islands, such as these
king penguins on South Georgia Island in the South
Atlantic Ocean, often exhibit uniform spacing,
maintained by aggressive interactions between
neighbors.
Random. Dandelions grow from windblown seeds
that land at random and later germinate.
Clumped Distribution


Density is the result of an interplay between
processes that add individuals to a population
and those that remove individuals
Additions to a Population



Immigration is the influx of new individuals from
other areas
Births of Individuals
Removal from a Population


Emigration is the movement of individuals out of
a population
Death of Individuals
Population dynamics
Births
Births
Births and immigration
add individuals to
a population.
Births and immigration
add individuals to
a population.
Immigration
Deaths
Deaths
Deaths
and
Deaths
and
emigration
remove individuals
from a population.
Emigration

Survivorship curves can be classified
into three general types:
 Type
I: low death rates during early
and middle life, then an increase
among older age groups
 Type
II: the death rate is constant
over the organism’s life span
 Type
III: high death rates for the
young, then a slower death rate for
survivors
Number of survivors (log scale)
Survivorship Curves
1,000
I
100
II
10
III
1
0
50
Percentage of maximum life span
100
Exponential Growth
Exponential population growth is
population increase under idealized
conditions.
 Under these conditions, the rate of
reproduction is at its maximum.
 Exponential population growth results
in a J-shaped curve
 Exponential Growth is not sustainable.

The J-shaped curve of exponential growth characterizes some
rebounding populations
Elephant population
8,000
6,000
4,000
2,000
0
1900
1920
1940
Year
1960
1980
Carrying Capacity

Carrying Capacity is the maximum number
of individuals of a given species the
environment can support.

The closer the population to the carrying
capacity, the greater the environmental
resistance.

Biotic potential is having full effect and birthrate is
a maximum during exponential growth.
Carrying Capacity
Limiting factor- any biotic or
abiotic factor that restricts the
existence of organisms in a
specific environment.
 EX.- Amount of water
Amount of food
Temperature
Logistic Growth (S Curve)
Number of Paramecium/mL
1,000
800
600
400
200
0
0
5
10
15
Time (days)
A Paramecium population in the lab
Factors That Affect Population Size

Density Dependent Factor
 Factor whose effect on population
changes as population density changes
 Examples:
 Predation
 Disease
 Competition
 Sometimes cause Boom-or-Bust
Population Cycles
Density Dependent Factors
Snowshoe hare
120
9
Lynx
80
6
40
3
0
0
1850
1875
1900
Year
1925
Number of lynx
(thousands)
Number of hares
(thousands)
160
Changes in predation pressure can drive population fluctuations
Number of wolves
Wolves
Moose
40
2,000
30
1,500
20
1,000
10
500
0
1955
1965
1975
1985
Year
1995
0
2005
Number of moose
2,500
50
Population Crash

Overshooting carrying capacity can lead to
population crash

Abrupt decline in population density
Factors That Affect Population Size

Density Independent Factors
 Factors that affects population size,
but is not influenced by changes in
population density
 Examples:
Killing frost
Severe blizzard
Fire
Moose population size
2,500
2,000
1,500
1,000
Dramatic collapse caused by severe
winter weather and food shortage,
leading to starvation of more than
75% of the population
500
0
1960
1970
1980
Year
1990
2000
Density
Independent:
Flood
2 Life History Patterns

R Strategists






short life span
small body size
reproduce quickly
have many young
little parental care
Ex: cockroaches,
weeds, bacteria
2 Life History Patterns
 K Strategists
 long life span
 large body size
 reproduce slowly
 have few young
 provides parental
care
 Ex: humans,
elephants
Reproductive Strategies
r-selected species
k-selected species
-Small body size
-Small broods
- Early maturity
-Long life span
- Short life span
-Slow development
- Large broods
-Large body size
- Little or no parental
-Late reproduction
care
-Low reproductive rate
- Probability of long term -Redwood trees and
survival is low
human beings
- Mosquitoes and
Dandelions
Types of Organism Interactions
Predation
Predator
Prey
Types of Organism Interactions
Competition
Types of Organism Interactions
Symbiosis
What it means:
Two organisms that live together
Temporarily or for a longer time
At least one of the organisms
benefits from the relationship
What are the different kinds of
symbiosis?
Mutualism
both organisms
benefit
Commensalism
Parasitism
one organism
benefits
one organism
is harmed
one organism
benefits
one organism
is unaffected
Symbiosis: Mutualism
Organism One
Organism Two
When both organisms receive some
benefit from the relationship.
Mutualism

The African
Honeyguide Bird and
the Honey Badger
 The bird finds
honey bee nests
and makes a
special call to
attract the badger,
who breaks open
the hive so both
can eat
Mutualism

Tick bird and
rhinoceros;
 The birds get food
(ticks) and
protection and the
rhino and ox get
parasites removed
Mutualism

The crocodile opens its mouth to let the Egyptian
Plover (a bird) pick leeches off of its gums
 The crocodile is rid of a parasite and the plover
gets a meal
Mutualism


Cleaner Wrasses
remove parasites
from larger fish
They have been
known to set up
“cleaning stations”
where fish can come
to get cleaned

Wrasses get food and
other fish get parasites
removed
Symbiosis: Commensalism
Organism One
Organism Two
Commensalism
The Remora attaches itself to the shark and saves
energy since it doesn’t have to swim, and it gets to eat
on the shark’s kills. The shark doesn’t get anything.
Commensalism

Certain species
of crab carry
venomous sea
urchins on their
backs
 Gives the crab
protection
from predators
Commensalism

Barnacles need a
place to anchor. They
must wait for food to
come their way. Some
barnacles hitch a ride
on unsuspecting
whales who deliver
them to a food
source. This does not
effect the whale in
any way.
Symbiosis: Parasitism
Organism One
Organism Two
•One organism benefits, the other one is negatively affected
•Win-Lose relationship
•Parasites rarely kill their hosts…it would require them to get
another one!
Parasitism

A tapeworm
attaches to the
intestinal wall of its
host and absorbs
nutrients
 This harms the
host because its
nutrients are
being diverted to
the parasite
Parasitism

Bedbugs are small,
nocturnal parasites
that come out of
hiding at night to
feed on unsuspecting
humans. They feed
exclusively on
blood! Their bites
often result in an
allergic reaction.
Parasitism

Leeches attach to
their victims and
inject an anticoagulant to keep the
blood from clotting
 Leeches get a
meal, and the
organism loses
blood and can get
open wounds
which can become
infected.