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. coliLichen (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