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How do species interact with one another to make stable Ecological Communities?

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Presentation on theme: "How do species interact with one another to make stable Ecological Communities?"— Presentation transcript:

1 How do species interact with one another to make stable Ecological Communities?

2 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.

3 +/- Ecological Effects of One species on the other Species 2 +- Species 1 + MutualismPredation - Competition

4 Ecological Effects of One species on the other Species 2 +- Species 1 + MutualismPredation - Competition

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

6 Mutualism is an interaction between two (or more) species that is beneficial (+) to both (all) species. Algae: + effects on fungi: algal photosynthesis produces sugars and oxygen for the fungus. Fungus: + effects on algae: fungus absorbs nutrients from the atmosphere and produces CO 2 which permits the alga to photosynthesize. Fungus also protects the alga from drying out.

7 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 spores and maintains optimal humidity for fungal growth. Fungus: + effects on beetle: fungus provides nutrition for the beetle.

8 Ant-Aphid mutualism Ants: protect the aphid from predators. Aphids: provide plant sugars for the ants

9 Ecological Effects of One species on the other Species 2 +- Species 1 + MutualismPredation - Competition

10 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.

11 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.

12 Paramecium caudatum Paramecium aurelia

13 Single Species Populations: each survives indefinitely when reared alone. Competition Populations: P. aurelia out-competes P. Caudatum when reared Together. Gause’s Experiments

14 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 Tribolium castaneum Thomas Park’s experiments

15 Single Species Equilibrium Population Sizes when reared ALONE Predict the Winner in Competition Climate T. castaneumT. confusum Cold-Dry Cold-Wet Warm-Dry Warm-Wet Hot-Dry Hot-Wet

16 Single Species Equilibrium Population Sizes when reared ALONE Predicted Winner in Competition Climate T. castaneumT. confusum Cold-Dry confusum Cold-Wet confusum Warm-Dry confusum Warm-Wet castaneum Hot-Dry confusum Hot-Wet ?Toss Up

17 Observed Competitive Outcomes: Percent Wins when raised together Predicted Winner in Competition Climate T. castaneumT. 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

18 Observed Competitive Outcomes: Percent Wins Predicted Winner in Competition Climate T. castaneumT. 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

19 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.

20 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 was not completely Predictable.

21 Changing the Hot-Wet Environment by ADDING a thrid species, the pathogen, Adelina tribolii Changed the identity of the winning species from 100% T. castaneum to 80% T. confusum.

22 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

23 Ecological Effects of One species on the other Species 2 +- Species 1 + MutualismPredation - Competition

24 Arms-Race Co-evolution Exploitative Ability of Predator Defensive Ability of Prey Selection by Predator on Prey Selection by Prey on Predator

25 Life-Dinner Principle Predator is hunting for its dinner. If it fails in an encounter with 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 a predator, it loses its life and the effect on prey fitness is very large. Natural Selection on the Prey species to evolve defenses is STRONGER than Natural Selection on the Predator Species to evolve hunting ability.

26 Arms-Race Co-evolution is Typically Asymmetrical Exploitative Ability of Predator Defensive Ability of Prey Selection by Predator on Prey is Strong Selection by Prey on Predator is Weak

27 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 of fitness 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 means a STRONG Arms Race

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29 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

30 Species of NewtSkin Toxicity in “Mouse Units” Taricha granulosa 25,000 Taricha torosa 1,000 –2,500 Taricha rivularis 1,000 –2,500 Notophthalmus viridescens 20

31 Range of Taricha (prey) species T. granulosa T. granulosa, T. torosa, T. rivularis T. granulosa, T. torosa

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33 Range of Thamnophis sirtalis Benton Tenmile Study Sites

34 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.

35 Prey Toxin [mouse units of TTX] Predator Resistance (% reduction) Coluber Resistant T. sirtalis ‘”Super” Resistant T. sirtalis Nonresistant

36 Geographic Variation in Snake Resistance NonResistant Weakly Resistant Strongly Resistant Super Resistant T. granulosa T. granulosa, T. torosa, T. rivularis T. granulosa, T. torosa Geographic Variation in Newt Toxicity


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