Download Ecology -Communities (Part 2)-

Ecology
-Communities (Part 2)-
Communities - Processes between Populations
+ = beneficial to a species
-  = detrimental to a species
0 = species is unaffected
Kinds of Interactions
Interaction
Species 1
Species 2
Competition
-
-
Predation
+
-
Herbivory
+
-
Parasitism
+
-
Disease
+
-
Mutualism
+
+
Commensalism
+
0
Communities - Processes between Populations
•  Competition
–  A (+, -) interaction between members of the
same species (Intraspecific) or between
members of different species (Interspecific)
for resources that are in short supply
–  Resources can be food, water, mates,
nesting sites etc.
Communities - Processes between Populations
•  Competition
1934 - Gause - Experiments with Paramecium
Paramecium aurelia
Paramecium caudatum
Communities - Processes between Populations
•  Competition
1934 - Gause - Experiments with Paramecium
P. aurelia alone
P. caudatum alone
previous P. aurelia
P. aurelia
P. caudatum
Grown together
Communities - Processes between Populations
•  Competition
From Gause’s Paramecium experiments
Competitive exclusion principle
When two species compete for the same
limited resource, one species will eventually
eliminate the other.
Communities - Processes between Populations
•  Competition
Ecological niche
The total of species’ use of biotic and abiotic
resources in its environment
Eugene Odum
- the habitat is a species address, the niche is its
“profession”.
Remember equation for logistic population growth
dN
(K - N)
rN
=
dt
K
Two new terms:
α = effect* of species 2 on species 1
β = effect* of species 1 on species 2
*‘effect’ means how much the growth of a population is decreased
Logistic population growth and competition
dN1
r1N1
=
dt
(K1 – N1- α N2)
K1
Effect of species 2 on species 1 depends on the degree of the effect (α) and the numbers of species 2
dN2
r2N2
=
dt
(K2 – N2- β N1)
K2
Effect of species 1 on species 2 depends on the degree of the effect (β) and the numbers of species 1
Logistic population growth and competition
α P. aurelia if alone
P. aurelia in competition
P. caudatum if alone
β
P. aurelia is species 1
Effect of aurelia on caudatum is β P. caudatum is species 2
Effect of caudatum on aurelia is α P. caudatum in competition
Communities - Processes between Populations
•  Competition
How do species respond to competition?
1.  Character displacement
Geographical
distribution of
species B
Geographical
distribution of
species A
Area of Sympatry
(and
competition)
Communities - Processes between Populations
•  Competition
How do species respond to competition?
1.  Character displacement
Geospiza fuliginosa
Geospiza
fortis
Communities - Processes between Populations
•  Competition
How do species respond to competition?
1.  Character displacement
Beak depth (and therefore the kind
of food eaten) changes in sympatric
area
Communities - Processes between Populations
•  Competition
How do species respond to competition?
2. Resource Partitioning
-differentiation of ecological niches that allows two
species to coexist
Communities - Processes between Populations
Myrtle warbler
Bay breasted
warbler
Cape May
warbler
All eat the same food
(insects) and live in the
same trees
Communities - Processes between Populations
•  Competition
2. Resource Partitioning
Cape May warbler
Bay breasted warbler
Myrtle warbler
Communities - Processes between Populations
•  Competition
2. Resource Partitioning
Communities - Processes between Populations
•  Mutualism
–  Any interaction between members of two
species that is beneficial to both
Communities - Processes between Populations
•  Mutualism - Corals and Algae
Gastrodermis
•
•
•
•
•
•
M
e
s
o
g
l
e
a
zooxanthellae
Ectodermis
Communities - Processes between Populations
•  Mutualism - Corals and Algae
Sugars to polyp
Nitrogen to zooxanthella
Communities - Processes between Populations
•  Predation
–  A (+, -) interaction between members of two
species in which one species kills and eats
members of the other
Communities - Processes between Populations
•  Predation
Predator and prey have co-evolved in response to
one another
Predator evolves some mechanism to be
a better predator
Prey evolves some
reponse to avoid
the predator
Communities - Processes between Populations
•  Predation
Some mechanisms for making predators more efficient
Incisor teeth (molars)
for piercing and holding prey
Carnassial teeth (molars)
for shearing meat
Communities - Processes between Populations
•  Predation
Some mechanisms for making predators more efficient
Spine
acts as a
spring to
give extra
thrust
when
running
Communities - Processes between Populations
How to avoid being prey
•  Predation
Mimicry
Either look like something distasteful
Have a number of distateful
animals resemble one another
or
Viceroy Monarch
Batesian Mimicry
Mullerian Mimicry
Communities - Processes between Populations
•  Predation
How to avoid being prey
Mimicry of other objects
Communities - Processes between Populations
•  Predation
How to avoid being prey
Evoke startle response
Communities - Processes between Populations
•  Predation
Populations of predators and
prey cycle slightly out of phase
with one another.
Top down vs bottom up controls
Two views on how community structure is controlled
Top-down mechanism
Bottom-up mechanism
Top-down control
Predator species
controls
Numbers of a
prey species
controls
Numbers of a
plant species
Top-down control
- Already seen an example of this
- after hunting of sea otters
Bottom-up control
Numbers of a
plant species
Nutrients controls
Numbers of a
prey species
controls
Predator species
Bottom-up control
Quantity and
quality of grass
Number of grasshoppers
Nitrogen, phosphorus