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Community Ecology II: Species Interactions. Ecological communities: Assemblages of two or more species living and interacting in the same area. Species interactions : the ways different organisms affect each other and how they have adapted to each other’s presence.

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Community ecology ii species interactions
Community Ecology II: Species Interactions


Ecological communities: Assemblages of two

or more species living and interacting in the same area.

Species interactions: the ways different organisms

affect each other and how they have adapted to each other’s presence.


FOUR main kinds of species interactions; all play

a role in the formation of community structure...

Competition (-,-)

Predation, parasitism (+,-)

Mutualism (+,+)

Commensalism (+,0)


Interspecific Competition:

Use or defense of a resource by one species

that reduces availability of that resource

to a different species.

exploitative competition

interference competition


Competition in paramecium
Competition in Paramecium


Competitive Exclusion:

A result of competition between species

for a limiting resource, in which one

species completely eliminates the other.


Ecological Niche:

  • a species’ ecological ‘role’

  • all the environmental factors that influence

  • the growth, survival, and reproduction of a species

  • an n-dimensional hypervolume within which

  • a species’ population growth is positive



Fundamental Niche vs Realized Niche

Fundamental Niche: the niche that a species potentially

could occupy, in the absence of competitors.

Realized Niche: the niche to which a species is restricted

in the presence of competitors.



EXPERIMENT

RESULTS

Ecologist Joseph Connell studied two barnacle species—Balanus balanoides and Chthamalus stellatus —that have a stratified distribution on rocks along the coast of Scotland.

When Connell removed Balanus from the lower strata, the Chthamalus population spread into that area.

This suggests that Balanus is the superior competitor, preventing Chthamalus from occupying the low tide zone.


When Balanus are removed from the intertidal zone, Chthamalus expands to occupy the space formerly occupied by Balanus. What would you predict if one removed Chthamalus?

A) Since Balanus is the superior competitor, it probably would move up into the space Chthamalus occupied.

B) Since Chthamalus is the superior competitor, it probably would move down into the space Balanus occupied.

C) Since Balanus is the superior competitor, it probably cannot live in the high intertidal zone.

D) Balanus would disappear as well, since it preys on Chthamalus.

E) Because of the mutualistic association, the range of Balanus would shrink.


Competitive Release:

Expansion of a species’ ecological

niche when a competitor is removed

(usually in a removalexperiment).


Q: How do similar species coexist?

A1: Resource Partitioning


Resource Partitioning

  • Species using similar resources can coexist when the habitat is spatially and temporally complex, thus allowing for niche specialization




FOUR main kinds of species interactions; all play

a role in the formation of community structure...

Competition (-,-)

Predation, parasitism (+,-)

Mutualism (+,+)

Commensalism (+,0)


True predators prey is killed immediately upon successful attack
True Predators - prey is killed immediately upon successful attack

Great White Shark, Siberian Tiger,

…Fox Squirrel?


Partial Predators- prey usually not killed but many prey organisms affected during predators lifetime - grazers, browsers

Giraffe, Bison, Monarch Caterpillar


Predators can influence species withincommunities by selecting for anti-predator adaptations in prey…




Morphological Defenses

Cryptic coloration

Flexible crypsis


Aposematic or warning coloration

Morphological & Physiological Defenses

Aposematic or Warning Coloration

Monarch Butterfly and Caterpillar


Blue jay eats monarch but vomits due to cardiac glycoside from milkweed
Blue jay eats monarch, but vomitsdue to cardiac glycoside from milkweed


E g wolves and moose on isle royale

Predators can also influence the abundance

and distribution of their prey.

e.g. Wolves and Moose on Isle Royale


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