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Interactions in Communities
• the two major categories of interactions in biological
communities are:
– intraspecific interactions
• intraspecific interactions
occur between members
of the same species
– “intra” means
“within” (e.g.
intramurals)
• example: competition for
mating partners
Interactions in Communities
•two major categories of interactions in biological
communities:
– interspecific
interactions
• interspecific
interactions occur
between members of
two different species
– “inter” means
“between” (e.g.
international)
• example: predator/prey
relationships
Interspecific Interactions
• Inter-specific interactions are classified
according to the benefit to each species
– predator-prey relationships
• one benefits, one is harmed
– interspecific competition
• both are harmed
– symbiotic relationships
• one benefits, the effect on the other varies
Predator – prey relationships
• Also known as
“predation”
• One organism kills and
feeds on another
organism
– The organism doing the
killing is the predator
– The organism being killed
is the prey
Predator – prey relationships
• predator and prey
populations tend
to go in cycles
– as prey populations
increase, the number
of predators increases
shortly thereafter.
• This is b/c as the
prey pop. goes up,
more predators
can feed on them,
they become
more healthy and
can have more
young.
Predator – prey relationships
• predator and prey
populations tend to go
in cycles
– Similarly, as prey
populations DE-crease, the
number of predators does
too,
• This is b/c as the
predator pop. goes up,
they require more food.
They consume the prey
pop. causing the
number of prey to
decline.
• As there is less food,
more competition
occurs and the predator
either dies, or must
move, causing their
numbers to decline as
well.
•
as prey evolve, predators must
evolve with them, or risk losing a
food source
Competition
• Interspecies competition occurs when members of
two different species compete
• both species must rely on the same resource
– Food
– Territory & shelter
Assignment:
– Investigation: Predator-Prey
Population Dynamics
(pg 420-421)
• Complete Analysis Q’s 1-5
Symbiosis
• symbiotic relationships
– close relationship between individuals of different species
that live together
– there are three types of symbiotic relationships
– classified according to the effect on the other species
• is the relationship…
– helpful to both?  mutualism
– harmful to one?  parasitism
– helpful to one, but non-consequential to the
other?  commensalism
Mutualism
– where both partners benefit
from the relationship
– example: the relationship
between flowering plants and
their pollinators
• when pollination is carried
out by bees, the bees
benefit by getting nectar
• the plant benefits by
getting its pollen dispersed
/ being pollinated
Commensalism
– when one partner
benefits, and the other is
unaffected
– example: the clownfish
lives in a type of coral
called an anemone
• normally the anemone stings
predators and digests it with
enzymes it secretes from its
tentacles
• the clownfish is immune to
the anemone’s sting because
of a special mucus secreted by
its skin
• the clownfish benefits from
having protection of the
anemone, but the anemone is
unaffected by the clownfish
Parasitism
– one partner benefits and the
other is harmed
• the partner who benefits is
called the parasite, while its
victim is referred to as the
host
– parasites are an important
factor in limiting the growth of
host populations
– they will never completely
wipe out a population,
because that would also cause
the parasite to become extinct
• parasitism
– parasites include all viruses, and some worms, bacteria, and insects
– parasites affect almost all species of wild and domesticated plants
and animals
– the World Health Organization estimates that 1.4 billion people
worldwide are infested with parasites
• equivalent to about 1 in 5,
• less developed areas are more susceptible due to
contaminated drinking water, lower standard of living,
and poorer nutrition
Assignment:
• PRACTICE PROBLEMS
– Q#’s 9, 10, 15, 16, 19,
20 (pg’s 414-418)
• 1.2 Summary Q’s 2-6
(pg 422)
The Biosphere
Section 1.3 of Life
The Web of Life
Roles of Organisms in an Ecosystem
• Producers
– organisms who use light
energy to create sugars
through photosynthesis
– produce organic
compounds that will
serve as food for other
organisms
• rely on sunlight,
water and nutrients
from the soil and air
Roles of Organisms in an Ecosystem
 Consumers
 organisms that rely on producers as a food source
– primary consumers
• rely directly on producers for
food
– called herbivores
– only eat green plants
– Ex. algae or plankton
Roles of organisms in an ecosystem
 Consumers
 organisms that rely on producers as a food source
– Secondary consumers
• feed on primary
consumers
• can be an omnivore or a
carnivore)
– An omnivore will feed on
both plants and animals
depending on availability
and opportunity
Roles of organisms in an ecosystem
 Consumers
 organisms that rely on producers as a food source
– Secondary consumers
• carnivores are
organisms that kill
and eat other animals
– most carnivores are
animals, but there
are a few carnivorous
plants
Roles of organisms in an ecosystem
 Consumers
 organisms that rely on producers as a food source
– tertiary consumers
• feed on secondary
consumers
• Usually the top
predator in the
ecosystem
• generally
carnivorous.