Transcript Community Interactions

Community Interactions
M4 Environment
Community Interactions

There are 3 basic types of interactions:
• Competition
• Predation
• Symbiosis
Competition
Competition
Organisms will compete for a number
of things:
Land territories
 Food
 Sexual partners
 Being closer to needed resources (ex. Sun)

When shared resources are in short
demand, organisms compete
Types of competition

There are 2 type of competition:
• Intraspecific competition
(competition between members of the
same species)
• Interspecific competition
(different species competing)
Competitive Exclusion
Also known as Gause’s principle
 No two species can occupy the same
niche indefinitely when resources are
limited. If this occurs one species
will always out compete the other,
and the extinction may occur if
natural selection (evolution) does not
reduce the competition between
them.

Character Displacement

To reduce overlapping
niches, natural
selection may change
the species so that
they can subdivide the
niche and live together
without direct
competition.
Figure: Darwin’s finches underwent
character displacement to avoid
competition. They now have different
niches (because of different beak size)
when they are living together on the same
island
Social Dominance
(Intraspecific competition)

Some organisms have a highly developed
organization which dictates which
member of the same species gets the best
resources.
• Dominant individuals
will exclude subdominant individuals
from resources
Example- Territorialism is a
form of competition where
dominant individuals get the
best areas to live
Dominance hierarchy (“pecking order”)
Social Dominance
Predation
Predation
Predation is a very important concept
in Ecology. All organisms need food
to live.
 A predator is an organism that feeds
directly upon another organism
(prey), whether or not it kills the
prey to do so.

Predation and Prey

Predation shapes
the natural
communities and
influences the
distribution and
abundance of prey.
Rabbit population without prey
Rabbit Pop. with Predation
Parasitism
Parasites are organisms that live on
or in other organisms ( the host),
taking nutrients from the host
without killing them (at least not
right away)
 Parasite are often smaller than their
hosts
 “Predator from within”

Parasite
Tapeworms are parasitic worms that infest the
intestinal lining of vertebrates. They do not have
mouths but absorb already digested food
Saprophylism

Saprophyte is any organism that cannot make
its food by photosynthesis, and instead gets its
nutriment from decaying organic matter.
Mushrooms, molds, and other types of fungi
are the most abundant saprophytes. Certain
types of bacteria are saprophytes, as are some
types of orchids
Saprophyta
Symbiosis
Symbiosis
Sym- together
 Biosis- life


Symbiosis means 2 or more species
forming a close relationship
Commensalisms
Commensalisms is a common
form of symbiosis
 One member of the association
benefits while the other is
neither harmed nor helped

Ex. Some orchids living on trees.
The orchid gets a place to live and
the run off of nutrients down the
tree trunk. The tree is neither
harmed nor benefits from the
orchid
Mutualism
Another form of symbiosis
 Mutualism is when both partners
benefit from the symbiotic relationship.

Examples
-Human intestinal bacteria E. coli within the colon
produce vitamin K, which the human body requires
for the process of blood clotting
-Birds eating insects off the backs of Rhinos
-Relationship between clown fish and sea anemones
Mutualism
The clown fish has developed a special relationship with the sea
anemone. The clown fish keeps away the anemone’s predators
and the sea anemone protects the fish with its tentacles armed
with stinging cells.
Mutualism
The relationship between the fungus and the alga in lichen is an example
of mutualism. This relationship enables each to tolerate harsh conditions
where neither could survive alone. In this partnership, the fungus furnishes
the alga with water and provides simple mineral nutrients, while the
photosynthesizing alga supplies food to the fungus.
Mutualism
Mycorrhizal Fungi
(Friendly Fungi)
 Fungus and roots
 The fungus absorbs
minerals and
supplies them to
the plant
 The plant provides
nutrients produced
by the plant to the
fungus
Coevolution

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2 species have a close ecological
relationship.
Co-evolution may occur in any symbiotic
relationship or other relationships.
Ex. host species that has a long history of
association with a particular parasite may
evolve a greater resistance to it.
They evolve together
Coevolution
These hummingbirds have coevolved with certain flowering plants,
So the long slender beaks of the bird will fix into the flower to receive
nectar. The plant will also deposit its pollen on the bird and the bird will
transport the pollen to another plant