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 resourceto a different species.

exploitative competition

interference competition

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 influencethe growth, survival, and reproduction of a species

• an n-dimensional hypervolume within which a species’ population growth is positive

3-dimensional niche

Fundamental Niche vs Realized Niche

Fundamental Niche: the niche that a species potentiallycould occupy, in the absence of competitors.

Realized Niche: the niche to which a species is restrictedin the presence of competitors.

Competition in Barnacles

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

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.

EXPERIMENT

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’ ecologicalniche when a competitor is removed(usually in a removal experiment).

Q: How do similar species coexist?

A1: Resource Partitioning

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

Resource Partitioning

Anolis spp.

Number of different Anole species on different islands

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

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 within communities by selecting for anti-predator adaptations in prey…

Behavioral Defenses

Morphological Defenses

Cryptic coloration

Flexible crypsis

Morphological Defenses

Aposematic or Warning Coloration

Monarch Butterfly and Caterpillar

Morphological & Physiological Defenses

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

e.g. Wolves and Moose on Isle Royale

Predators can also influence the abundanceand distribution of their prey.