BIOLOGY 403:
PRINCIPLES OF ECOLOGY
(Niche and Species-Species Interactions)
THE ECOLOGICAL NICHE I
• We have all probably used the term ‘niche’
before.
• What does it mean?
• DEFINITION
• a species functional role (“place”) in a
community in relation to other species
THE ECOLOGICAL NICHE (II)
• It is more than just the physical place (‘address’)
where a species lives, it also includes its role in the
system (its “occupation / lifestyle”).
• The Ecological Niche is a multidimensional
(‘hypervolume’) concept that includes where an
organism lives AND also includes what it does,
how it does it, when it does it, etc. It is its total
role in the ecosystem.
‘TYPES’ OF NICHE
• Fundamental or Hypothetical
the total range of physical, chemical and biological
factors a species can utilize / survive if there are
no other species affecting it
• Realized or Actual
that portion of the fundamental niche that a
species actually uses.
Species never live under ‘perfect’ conditions but
where an ‘acceptable’ ECOLOGIC SUM of
conditions exists.
NICHE EXCLUSION PRINCIPLE
(= Competitive Exclusion Principle)
(= Gause’s Law)
• DEFINITION
In a stable community no two species can occupy
the same niche
That is to say, no two species can coexist if they
need all the same things in the same place, at the
same time, etc.
• The greater the degree of niche overlap, the
greater the competition for scarce resources AND
the more likely one species will eliminate the
other.
GAUSE & PARAMECIUM
(too much niche overlap)
LIMITING NICHE OVERLAP (I)
LIMITING NICHE OVERLAP (II)
LIMITING NICHE OVERLAP (III)
INTERSPECIFIC INTERACTIONS
• Neutral Interactions
none of the interacting species is affected by the
others
Is this really possible???????????
• Positive Interactions
at least one of the interacting species is benefited
and the other(s) is (are) not harmed
• Negative Interactions
at least one of the interacting species is harmed
during the interaction
Positive Interactions (I)
• Commensalism
one species is benefited and the other(s) is (are) not
affected
without continuous contact : Vulture / Predator
with continuous contact: Turtle / Alga
• Protocooperation
both species are benefited BUT the relationship is
NOT obligatory
without continuous contact: Squirrel / Oak Tree
with continuous contact: some Mycorrhizae (a
fungus / plant root relationship)
Positive Interactions (II)
• Mutualism
both species are benefited AND the relationship IS
obligatory
without continuous contact:
many Pollinator / Plant relationships
with continuous contact:
Termites / Protozoans
Humans / E. coli
Lichen (alga / fungus)?
most Mycorrhizae (fungus / plant root
relationships)
NEGATIVE INTERACTIONS (I)
• Competition
both species are harmed during the interaction
• Imperfect
neither species is eliminated but one or both are
reduced in number (some niche overlap)
Pontin’s work with 2 species of ants of the genus
Lasius
• Perfect
one species is eliminated (too much niche overlap)
Gause’s work with 2 species of Paramecium
NEGATIVE INTERACTIONS (II)
• Predation
one is helped (fed) --- one is harmed (eaten);
a direct attack in which one species (the predator)
benefits by killing and eating another (the prey)
Wolf / Deer
Are both helped??????
• Parasitism
one is helped (fed) --- one is harmed (weakened);
a direct attack in which the parasite benefits by
taking small quantities of materials from its host
over an extended period of time and generally does
not kill the host.
Tape Worm / Human