Remember, a species, such as homo
sapiens, can exist in many places. The
population is all the members of the
species living in the same place at the
same time!
Note that the
word
POPULATION
refers to the
group in
general AND
the size of the
group!!
DENSITY
NUMBER of individuals
PER UNIT AREA (or
volume)
the number of
individual organisms
in a space
This is often related to
habitat quality
Fluctuations in density
reflect changes in the
local conditions (new
parasite, abiotic
factors change, etc)
Dispersion is the distribution or arrangement of
organisms in the habitat
Most populations are clumped. Why?
Resources are not uniformly distributed
Protection of the group / Pack living gives some predators
greater success
Temporary mating or young-rearing groups / seed distribution
Age structure – Who can add to
population?
Pre-reproductive stage
Reproductive stage
Post-reproductive stage
Growth
Rate
Births
Deaths
How fast a population’s size changes
over time is called a growth rate.
Growth rates can be positive… what
would that mean?
Growth rates can be negative… what
would that mean?
Growth rates can be zero… what would
that mean?
Lab Time
How do you think MIGRATION affects
growth rate?
Immigration would ADD to
population
Emigration would SUBTRACT from
population
Growth
Rate
Births
+
Immigration
Deaths
+ Emigration
Biotic Potential is the fastest rate at
which a population can grow.
Limited by reproductive potential, or
the maximum number of offspring a
member can produce
Also limited by generation time: the
average time needed to reach
reproductive age.
Mosquito:
- has thousands of kids
- able to reproduce in
days!
- population growth?
MONGO!
Elephant:
-Has less than 10 offspring
- Takes 13 years before
able to reproduce
- Population growth?
Pitiful!
Exponential growth
occurs in nature only
when populations have
plenty of food and space
No competition or
predators can exist
Often occurs with exotic
or invasive species!
(why??)
Australia’s Mccaw
Island
After rabbits were
introduced…
Where’s Elmer Fudd when you need him??
What causes exponential growth to
be limited?
Limiting Resource
Habitat loss
Disease
Disaster (natural or manmade)
Competition
Predator-Prey relationships
The natural resource
that inhibits growth is
called the LIMITING
RESOURCE. Habitat
loss can increase
potential candidates
for this
Competition, disease,
and predation also
limit population
growth.
Many times,
members of a
species will carve
out TERRITORY to
avoid competition
How do different
species mark out
territory? Birds?
Dogs? Trees?
Habitat Loss is also listed as a
means in which growth is inhibited
How would this affect population
growth?
It would speed up the use of the
limiting resource, increasing death
rate.
-The theoretical
limit that a
habitat can
support is called
the carrying
capacity.
-What pattern do
you see over
there ?
Population size (N)
Environmental
resistance
Carrying capacity (K)
Population stabilizes
Exponential
growth
Biotic
potential
Time (t)
Beyond resource and habitat
limitations, other factors, such as
disease and disaster can regulate
populations
We divide all population limiting
factors into DENSITY DEPENDENT
and DENSITY INDEPENDENT
regulation
Density Dependent
Definition: deaths occur more
quickly when population is
crowded.
Most limiting factors are
density dependent.
Example – disease: needs to
spread from organism to
organism.
Example – competition: the
more individuals in an area,
the less of a resource is
available to each.
Density Independent
When the cause of
death is density
INDEPENDENT, a
proportion of the
population will die,
regardless of
congestion.
Weather and disasters
are examples
Let’s Classify Some, shall we?
Species are never alone in an
ecosystem.
In order to survive, any population
must carve out its unique role within
the ecosystem – called its NICHE.
A niche includes the species’ physical
home, the environmental factors
necessary for the species’ survival,
and all the species’ interaction with
other organisms!
The Way that SPECIES INTERACT
can accentuate or inhibit population
growth.
We’ve discussed these relationships
before, but now we’re going to study
them in depth
Interaction
Species A
Species B
Description
Competition
Harmed
Harmed
Each species negatively
impacts the other
Predation and
Parasitism
Benefited
Harmed
Species A feeds on
Species B
Mutualism
Benefited
Benefited
Each species is helpful to
the other
Unaffected
Species A benefits from
species B, Species B is
unaffected
Harmed
Species A may benefit
from the death of species
B
Commensalism
Amensalism
Benefited
Unaffected
A relationship in which two organisms
live in close association is called
symbiosis
Usually, at least one of the organisms
benefits
Over time, species in close relationships
may coevolve – that is, they evolve
adaptations that reduce the harm or
improve the benefit of the symbiotic
relationship
As we go through relationships, see if
you can spot the coevolutions!
Predation
Competition
Parasitism
Species
Interactions
Amensalism
Mutualism
Commensalism
Competition is a relationship in which
different INDIVIDUALS OR
POPULATIONS attempt to use the
same limited resource.
It occurs within and between species
When species compete, we say their
niches overlap.
Species can compete even if they
never come in contact.
Day feeders and nocturnal animals
may all use the same water hole –
they are indirectly competing.
Humans rarely interact with potato
bugs, but we’re in competition for
potatoes.
In the course of evolution,
adaptations that decrease
competition will be advantageous
when niches overlap.
Niche restriction is when each
species uses LESS of the niche than
they are capable of using (for
example, territory restriction)
Predation
Competition
Parasitism
Species
Interactions
Amensalism
Mutualism
Commensalism
An organism that feeds on another
organism is called a predator.
The organism that is fed upon is the
prey.
This interaction is predation.
This is NOT as simple as it seems.
Sometimes predators are prey!
Most organisms have developed
predation defense mechanisms.
Predation
Competition
Parasitism
Species
Interactions
Amensalism
Mutualism
Commensalism
An organism that lives in or on
another organism and feeds on the
other organism is called a parasite.
The organism that the parasite steals
nourishment from is called the host.
Parasites are somewhat like
predators, the difference being that
parasites live IN or ON the host.
Predators only eat the host.
Common parasites of the human body
(1) The hookworm latches on the walls of the colon with
its sharp teeth where it feeds on blood. (2) The tapeworm
is the longest parasite. A mature adult can lay a million
eggs a day. (3) Tapeworm eggs embedded in the colon.
(4) The roundworm can grow to be 20 inches (50 cm)
long and lay 200,000 eggs per day. (5) Pinworms migrate
outside the colon during the night to lay their eggs
around the anus. This causes the nightly itching of many
unsuspecting victims.
Predation
Competition
Parasitism
Species
Interactions
Amensalism
Mutualism
Commensalism
A close relationship between two
species in which each species
provides a benefit to the other is
called mutualism
Algae in coral is mutualistic
The bacteria in your gut is
mutualistic
Predation
Competition
Parasitism
Species
Interactions
Amensalism
Mutualism
Commensalism
When one species benefits, but the other
species is unaffected, the relationship is
called COMMENSALISM.
Remoras, for example, either hitch a ride
on bigger animals, or they eat food
scraps from the bigger animal, or both…
Mimicry can be another type – One
organism looks like another, for a reason.
They benefit, and the ones they mimic
are unaffected.
Predation
Competition
Parasitism
Species
Interactions
Amensalism
Mutualism
Commensalism
A symbiotic relationship in which one
species is unaffected but the other is
harmed.
Often, the second species is actually
terminated. Think about grass being
tramped by people.
Sometimes, the surviving species uses the
nutrients from the terminated species, so
there is benefit.
As an example, many plants secrete
substances that inhibit or kill neighboring
plants! They then may use the detritus of
the dead plants as nutrition!
The Black Walnut
Penicillium!