1. science
2. biology
3. zoology
4. endangered species

Community Ecology
• Community: interacting species within a
given area
• Spatially:
– Population < Community < Biome
Species Interactions
•
•
•
•
Interaction between 2 species.
Affect fitness of both species
Fitness effects: +, -, or 0
Five basic types of interactions
Direct Interactions
commmensalism
0
A
B
A
+
B
amensalism
A
competition
0
A
B
+
Consumption
(antagonistic)
B
+
A
+
mutualism
B
Commensalism
• +/0
• One species gains in fitness
• Other species unaffected
Remoras and large fish/whales
•Remora gets protection, food
scraps, free ride
•Host not affected
Fat innkeeper worm and guests
•Worm creates safe, well ventilated burrow for
•Goby (fish)
•Pea Crab
•Scale worm
•“borders” have no fitness impact on worm
Mutualistic Interactions:
+/+
• Both organisms benefit
• Not cooperative or altruistic
– Rare case where:
– Both organisms attempt to profit
– Both are successful
• May change to consumptive/competitive
relationships
Ant – Plant Interactions
•Acacia tress: provide home to ants, sometimes food
•Ants: defend trees from grazers
•Plants with ants demonstrate better survival and growth
Mutualism between clown fish and anemone
Mutualism between pollinators and flowers
Competition
• -/• Both species experience fitness decrease
• Niche:
– sum total resources used by a species.
– Range of conditions it can tolerate
• Species with overlapping niches compete
with each other
Competitive Exclusion
• G. F. Gause
– Hyptothesized that 2 spp with same niche
cannot co-exist
• = competitive exclusion principle
2 types of Competition
• Symmetric
– Each spp. experiences the same decrease in
fitness
• Asymmetric
– One spp. has greater fitness decrease than
other
• Asymmetric more common than
symmetric
Why doesn’t asymmetric competition
cause there to be just a few superior
competitor species?
• Most niches don’t completely overlap
• This provides a spatial refuge for the
inferior competitor
Species 1 is the superior
competitor but species 2 can
retreat to the region of its
niche that doesn’t overlap
with species 1.
What would you predict
the shape of the curves on
the bottom to look like
after some time if
- Species 1 was a better
competitor for the
second largest seed
class?
- Species 2 was a better
competitor for the
second largest seed
class?
Fundamental vs Realized Niche
• Fundamental niche: total possible use of
the environment by a spp.
• Realized niche: actual observed used of
the environment by a spp.
Classic example: Little and big barnacles in the intertidal
Cthamalus
High
Balanus
Mid
Low
Area where both barnacles settle
Cthamalus
High
Balanus
Mid
Death due to desiccation
Overgrown by
Balanus
Low
Overgrown by Mussels and
preyed on by whelks
Cthamalus
Balanus
Realized Niche
High
Mid
Low
Fundamental niche
Two categories for competitive
interactions
• Interference competition
– Species interfere with another’s use of a
resource
• Exploitation competition
– Species both utilize a resource
– Most efficient consumer wins
Interference Competition
Exploitation Competition
Consumption
(antagonistic interactions)
• One spp consumes all or part of another
• 3 types
– Herbivory
– Parasitism
– Predation
Herbivory
grazing organisms (herbivores) consume plant tissues
Parasitism
parasite consumes relatively small amounts of tissue from a
plant or animal (host)
Predation
predator kills and consumes all or most of another organism (prey)
Defense from Consumption
• Prey evolve defenses to counter predators
• Two basic types of defenses
– Constitutive: always presented
– Inducible: produced in response to
predators
Certain Defenses are advertised
• Aposematism:
• Warning colorations that advertise defenses
• Eg bright colors, striped patterns
Mimicry
• Constitutive defenses have led to 2 types
of mimicry
• Mullerian mimicry
– Spp. with similar defenses resemble each
other
• Batesian mimicry
– Spp. without defenses resemble those with
defenses
Inducible defenses
•
•
•
•
Variable responses
Triggered by presence of predators
Defense represents a fitness cost
Inducible defense minimizes fitness cost
Top down vs bottom up control of
consumption
• Predator/prey populations undergo
cycles
• What controls these cycles?
• Bottom up: amount of prey regulates
predator abundance
• Top down: predators control prey
abundance
One example: Lynx and Arctic Hare
Experimental setup to test the relative influence of top down
vs bottom up control
… but food supply (bottom up) influence is larger