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: algal photosynthesis produces sugars andoxygen for the fungus.

Fungus: + effects on algae: fungus absorbs nutrients from the atmosphere and produces CO2 which permits the alga

to photosynthesize. Fungus also protects the alga from dryingout.

Mutualism is an interaction between two (or more) species that is beneficial (+) to both (all) species.

Beetles: + effects on fungi: the beetle ‘plants’ the fungal sporesand maintains optimal humidity for fungal growth.

Fungus: + effects on beetle: fungus provides nutrition for the beetle.

Ant-Aphid mutualism

Ants: protect the aphid from predators.

Aphids: provide 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: each survives indefinitely when reared alone.

Competition Populations:P. aurelia out-competes

P. Caudatum when reared Together.

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 Sizes 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 Sizes when reared ALONE Predicted

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

Observed Competitive Outcomes:

Percent Wins when raised together Predicted

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

Observed Competitive Outcomes:

Percent Wins Predicted

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 Predictions

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.

With T. castaneum and T. confusum,One species won and the other went extinct

in every one of the 170 competition populations

Where they were raised together.

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 was not completely

Predictable.

Changing the Hot-Wet Environment by ADDING a thrid species, the pathogen,

Adelina triboliiChanged the identity of the winning species

from 100% T. castaneum to 80% T. confusum.

Predator-Prey Arms Races:Reciprocal Co-Evolution of Offense and

Defense

Evolution of Garter Snake (Predator)

Exploitation Newt (Prey)

Evolution of Newt (Prey) Defense

against Garter Snake (Predator) predation

Ecological Effects of

One species on the other

Species 2

+ -

Species 1+ Mutualism Predation

- Predation Competition

Arms-Race Co-evolution

Exploitative Ability of Predator

DefensiveAbility of Prey

Selection by Predatoron Prey

Selection by Preyon Predator

Life-Dinner Principle

Predator is hunting for its dinner. If it fails in an encounterwith a prey, it loses only a meal and the effect on predator fitness is relatively small.

Prey is running for its life. If it fails in an encounter with apredator, it loses its life and the effect on prey fitness is very large.

Natural Selection on the Prey species to evolve defensesis STRONGER than Natural Selection on the Predator

Species to evolve hunting ability.

Arms-Race Co-evolution is Typically Asymmetrical

Exploitative Ability of Predator

DefensiveAbility of Prey

Selection by Predatoron Prey is Strong

Selection by Preyon Predator is

Weak

Intensity of Coevolution depends upon the Reciprocity of the fitness effects of Predator on Prey

and Prey on Predator.

Life-Dinner Principle suggests a lack of reciprocity offitness effects, and thus the intensity of coevolution

resulting from the arms race is weak.

However, when Prey are Dangerous or Toxic, then Dinner for the Predator means a risk of Death.

This Reciprocity of the fitness effects meansa STRONG Arms Race

Tetrodotoxin in skin of Newt.

Na+ channel blocker, causes paralysis.

Toxic to most animals.

Found in crabs, fugu fishes, annelid worms and algae.

Possibly produced by symbiotic bacteria

Species of Newt Skin Toxicity in

“Mouse Units”

Taricha

granulosa

25,000

Taricha

torosa

1,000 –2,500

Taricha

rivularis

1,000 –2,500

Notophthalmus

viridescens

20

Range of Taricha (prey) species

T. granulosa

T. granulosa,T. torosa,T. rivularis

T. granulosa,T. torosa

T. torosa

Range of Thamnophis sirtalis

Benton

Tenmile

Study Sites

Bioassay of Predator Resistance to Tetrodotoxin

1. Measure baseline speed

2. Inject known dose of TTX.

3. Measure post-injection speed.

4. “TTX resistance” is the % reduction in speed after injection of toxin.

Prey Toxin [mouse units of TTX]

Pre

dato

r R

esis

tanc

e (%

red

ucti

on)

0

50

100

0.01 0.1 1 10 100 1000 10000

ColuberColuber

ResistantResistantT. sirtalisT. sirtalis

‘”‘”Super” ResistantSuper” ResistantT. sirtalisT. sirtalis

NonresistantNonresistantT. sirtalisT. sirtalis

Geographic Variation in Snake Resistance

NonResistant

Weakly Resistant

Strongly Resistant

Super Resistant

T. granulosa

T. granulosa,T. torosa,T. rivularis

T. granulosa,T. torosa

T. torosa

Geographic Variation in Newt Toxicity