Why are there so many different
kinds of organisms?
How do species interact with one
another to make stable
Ecological Communities?
Ecological Effects of Species 1 on
Species 2:
(A) Effect is Positive (+) if species 1
increases the numbers of species 2.
(B) Effect is Negative (-) if species 1
decreases the numbers of species 2.
Species 2
Ecological Effects of
One species on the other
+
-
+
Mutualism
Predation
-
Predation
Competition
Species 1
Species 2
Ecological Effects of
One species on the other
+
-
+
Mutualism
Predation
-
Predation
Competition
Species 1
Mutualism is an interaction between
two (or more) species that is
beneficial to both (all) species.
Mutualism is an interaction between
two (or more) species that is
beneficial to both (all) species.
Algae: + effects on fungi, photosynthesis produces nutrients
for the fungus.
Fungus: + effects on algae, provides nutrition and some
chemical defenses.
Lichens: Mutualism between fungus, cyanobacterium and algae
> 13,500 species of lichens
"Ambrosia" Beetles Scolytidae
feed on fungi growing in galleries
Beetles
carry fungal
spores and
keep galleries
at optimal
humidity for
fungal growth
Xyleborus dispar: feeds on fungi growing in galleries
Mutualism is an interaction between
two (or more) species that is
beneficial to both (all) species.
Beetles: + effects on fungi, ‘plant’ the fungal spores
and maintain optimal humidity for fungal growth.
Fungus: + effects on beetle, provides nutrition and some
chemical defenses.
Ant-Acacia Mutualism
Acacia Tree: provides shelter
and food for the ants
The Ants: provide protection
against fire, caterpillars and
herbivorous mammals for
tree.
Acacia Tree
provides
nectar and
protein and
hollow thorns
for ant colony.
Ant-Aphid mutualism
Ant: protects aphid
from predators.
Aphid: provides plant
sugars for the ants
Species 2
Ecological Effects of
One species on the other
+
-
+
Mutualism
Predation
-
Predation
Competition
Species 1
Competition occurs when of two
species each require the same limited
resource. The availability of the
resource to one species is negatively
influenced by the presence of the
other species. It is a "-/-" interaction.
Gause’s Competitive Exclusion Principle:
When two species make similar demands
on a limited resource, then one or the other
species will go extinct as a result of
competition for the resource.
Paramecium caudatum
Paramecium aurelia
Gause’s Experiments
Single Species Populations
Competition Populations
Competition occurs when of two
species each require the same limited
resource. The availability of the
resource to one species is negatively
influenced by the presence of the
other species. It is a "-/-" interaction.
Tribolium
confusum
Thomas Park’s
experiments
Tribolium
castaneum
Single Species Equilibrium Population
Size when reared ALONE
Climate
T. castaneum T. confusum
Cold-Dry
21
208
Cold-Wet
99
225
Warm-Dry
150
237
Warm-Wet
401
264
Hot-Dry
77
190
Hot-Wet
306
329
Predict the
Winner in
Competition
Single Species Equilibrium Population
Size
Climate
T. castaneum T. confusum
Predict the
Winner in
Competition
Cold-Dry
21
208
confusum
Cold-Wet
99
225
confusum
Warm-Dry
150
237
confusum
Warm-Wet
401
264
castaneum
Hot-Dry
77
190
confusum
Hot-Wet
306
329
Toss Up
Competitive Outcomes: Percent Wins
Climate
T. castaneum T. confusum
Predicted
Winner in
Competition
Cold-Dry
0%
100%
confusum
Cold-Wet
30%
70%
confusum
Warm-Dry
13%
87%
confusum
Warm-Wet
86%
14%
castaneum
Hot-Dry
10%
90%
confusum
Hot-Wet
100%
0%
Toss Up
Unusual Outcomes based on Single Species Population Size
Competitive Outcomes: Percent Wins
Climate
T. castaneum T. confusum
Predicted
Winner in
Competition
Cold-Dry
0%
100%
confusum
Cold-Wet
30%
70%
confusum
Warm-Dry
13%
87%
confusum
Warm-Wet
86%
14%
castaneum
Hot-Dry
10%
90%
confusum
Hot-Wet
100%
0%
Toss Up
Gause’s Competitive Exclusion Principle:
When two species make similar demands
on a limited resource, then one or the other
species will go extinct as a result of
competition for the resource.
One species won and the other went extinct
in every one of the 170
Tribolium competition populations
Changing the Climate from
Hot-Wet to Cold-Dry
Changed the identity of the winning species
from T. castaneum to T. confusum.
Stochastic Outcome: In Intermediate Climates
each species won in at
least some of the competition populations.
The outcome of competition is not completely
Predictable.
Interactions of More than Two Species
T. Castaneum vs T. confusum: -, - interaction = Competition
Hot-Wet: T. castaneum wins 100%
Cold-Dry: T. confusum wins 100%
Change Environment by ADDING a pathogen
Adelina tribolii: protozoan pathogen of beetles
T. castaneum vs T. confusum with Adelina tribolii:
Hot-Wet: T. confusum wins 80%
Changing the Environment by
ADDING the pathogen
Adelina tribolii
Changed the identity of the winning species
from 100% T. castaneum
to 80% T. confusum.
Stochastic Outcome: In Intermediate Climates
each species won in at
least some of the competition populations.
The outcome of competition is not completely
Predictable.
Interactions of More than Two Species
Ant-Aphid-Tree:
Pairwise Interactions:
Ant-Aphid: +, + interaction = mutualism
Aphid-Tree: +, - interaction = herbivory
Caterpillar-Tree: + , - interaction = herbivory
Caterpillar-Aphid: 0 , 0 interaction
Four-Way Interaction
Ant-Aphid-Tree: +, +, + since ants remove
caterpillars which have a larger
negative impact on tree.
Caterpillars: removed from system by ants.