Transcript Lecture #1 Dynamics of Population growth & Feeding

Lecture #1 Dynamics of Population
growth & Feeding Relationships
Unit 8 Community
Interactions
Limiting Factors (resources) – factors
that limit the growth and/or reproduction
of an organism or population.
Can you think of an example?
There are two types of limiting factors
1. Density Independent Limiting Factorsenvironmental factors that affect population size
regardless of the population’s density
• Many density independent limiting factors are
abiotic factors.
Examples: long periods of hot or cold weather,
natural catastrophes ( forest fires, floods,
volcanic eruptions)
Density Dependent Factors
2. Density Dependant Limiting Factors –
Limiting factors that affect large, dense
populations more strongly than small, less crowded
ones.
Example: Predators, available food
Summarizing what you’ve learned
Would a drought be a density independent
or dependent limiting factor? Explain.
Would an infectious disease be a density
independent or dependent limiting factor?
Explain.
How Organisms Interact in
Communities
In an ecosystem, all members of the web
interact with one another.
• The interactions that we see are the
result of a long evolutionary history in
which many of the participants of the
ecosystem adjust to one another over
time.
Example – Flowering
plants evolved to
have an efficient way
to disperse their
pollen(reproduction)
How?
They let animals do it
for them!
Animals that feed on
pollen get a meal out
of the relationship
that they have with
the flowering plants
Coevolution – The
back- and – forth
evolutionary
adjustments between
interacting members
of an ecosystem
Examples • Wolf & Elk
• Bees & Flowers
• Cow & bacteria in
their rumen
Feeding Relationships
There are 3 main types of feeding
relationships in nature.
1. Predator- Prey
2. Parasite- Host
3. Plant- Herbivore
1. Predator- Prey
Predation - the act of
one organism feeding
on another.
Examples –
Lion feeding on a
Zebra; Spider feeding
on a centipede
Predator – any
Animal that lives
by preying on
other animals
(usually) from a
lower trophic level.
• Predators have
evolved to be
stealthy, swift,
strong, sharp
teeth/ claws, etc
Prey - any animal
species that is fed
upon by another
• Prey species have
evolved ways to
escape, avoid, or
fight off
predators.
Predator- prey balance . Predators and their
prey have evolved to keep each other’s
population in check
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As
As
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prey increases, predators increase.
predators increase, prey decreases
prey decreases, predators decrease
predators decrease, prey increases
Carrying Capacity- the maximum population
size of the species that the environment can
sustain indefinitely, given the food, habitat,
water and other necessities available in the
environment
2. Parasite-Host
Parasitism (a type of predation) – one
organism feeds on and lives in or on
another organism, bringing them harm.
• Parasites are much more abundant and
ecologically important than predators in
population control
• All species of plants and animals (even
microbes) can be infected with parasites
Parasite – an organism
that lives in association
with another organism
(host), from which it
obtains organic nutrition.
• This causes harm to
the host.
Host – The organism on/
in which a parasite
lives. It is the “prey”
of a parasite
Vector - the organism
that carries a parasite
from one host to
another.
Example - Mosquitoes
(disease carrying
Insects) carry malaria
and West Nile virus
Parasites don’t usually kill their hosts, but
they can in some cases.
Why do you suppose they don’t usually kill
their hosts?
No place like home……..
Answer: Because they
depend on the host for
a place to live and a
food source!
2 Types of Parasites
External parasites
(Ticks, mosquitoes,
fleas, lice, chiggers)
• They feed on the
host’s outer surface.
2 Types of Parasites
Internal parasites
(tapeworm, ascaris,
hookworm, heartworm in
canines)
• The live within the
body of their host.
• For example, the
tapeworm attaches in
the small intestine,
where it takes
nutrients from its
host.
Tapeworm scolex and suckers
Parasite- host balance
As the population density of a parasite
host increases, parasites and their
vectors have an easy time finding new
hosts.
• This means that infection rates
increase, and die-off results. This helps
to control population growth.
As the population density of the hosts
decrease, transfer of infection is less
because there are fewer individuals.
• This means a decrease in infection and
the population is usually able to recover
3. Plant- Herbivore
How the relationship works: Herbivores eat
plants.
• If the amount of available vegetation
decreases, the population of the herbivore
decreases.
• If the population of herbivore increases, the
relative amount of vegetation decreases.
Plant-Herbivore balance may only exist if a
predator or a parasite is limiting the population of
The herbivore.
If not, what happens to the ecosystem?
Overgrazing - the practice of grazing too many
livestock for too long a period on land that is then
unable to recover its vegetation.
Can plants defend themselves against
from herbivores?
Plants protect themselves from herbivores in a
Variety of ways.
Examples
• Thorns, spines
• “Chemical warfare”.
(Toxic chemical
compounds that discourage herbivores from
feeding on them.)
How do herbivores overcome the
defenses of plants?
Some herbivores have
evolved the ability to
feed on plants that
are “protected” by
particular defensive
chemicals.
Example
Monarch butterfly
caterpillars and milk
weed
• The milkweed's
"milk“ or white latex
is both acidic and
somewhat poisonous
to many animals.
• A female monarch lays its eggs on a
sprouted milkweed plant
• Once the eggs hatch, the monarch
caterpillar feeds solely on milkweed, and
stores the toxin in its body for life.
• Because of this, predators avoid
monarch’s because of their awful taste!
Take 2 minutes to summarize how the
interactions of community members may
help to keep populations in check.