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 onSpecies 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.
Ecological Effects of
One species on the other
Species 2
+ -
Species 1+ Mutualism Predation
- Predation Competition
Ecological Effects of
One species on the other
Species 2
+ -
Species 1+ Mutualism Predation
- Predation Competition
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 nutrientsfor 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
Beetlescarry fungalspores and
keep galleriesat 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 sporesand 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
Ecological Effects of
One species on the other
Species 2
+ -
Species 1+ Mutualism Predation
- Predation Competition
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
Single Species Populations
Competition Populations
Gause’s Experiments
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.
Triboliumconfusum
Triboliumcastaneum
Thomas Park’s experiments
Single Species Equilibrium Population Size when reared ALONE Predict the
Winner in
CompetitionClimate 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
Single Species Equilibrium Population Size Predict the
Winner in
CompetitionClimate T. castaneum T. confusum
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 WinsPredicted
Winner in
CompetitionClimate T. castaneum T. confusum
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
Competitive Outcomes: Percent WinsPredicted
Winner in
CompetitionClimate T. castaneum T. confusum
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
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 Climateseach 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 pathogenAdelina 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 triboliiChanged the identity of the winning species
from 100% T. castaneum to 80% T. confusum.
Stochastic Outcome: In Intermediate Climateseach 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 = herbivoryCaterpillar-Aphid: 0 , 0 interaction
Four-Way InteractionAnt-Aphid-Tree: +, +, + since ants remove
caterpillars which have a larger negative impact on tree. Caterpillars: removed from system by ants.