Download Community Ecology II: Competition & Predation

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
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
3-dimensional niche
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.
Competition in Barnacles
EXPERIMENT
Ecologist Joseph Connell studied
two barnacle species—Balanus balanoides and
Chthamalus stellatus —that have a stratified
distribution on rocks along the coast of Scotland.
RESULTS
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 removal experiment).
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
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
Morphological Defenses
Cryptic coloration
Flexible crypsis
Morphological & Physiological Defenses
Aposematic or Warning Coloration
Monarch Butterfly and Caterpillar
Blue jay eats monarch, but vomits
due to cardiac glycoside from milkweed
Predators can also influence the abundance
and distribution of their prey.
e.g. Wolves and Moose on Isle Royale