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Slide 2 of 20
Community
Def. – group of populations (different species) that live close enough to interact
Interspecific Interactions - How the populations in a community interact with the environment & each other Some of the key relationships in the life of an organism
are with OTHER species
IF the key relationship was with members of the same species, then the relationships would be called intraspecific interactions
Slide 3 of 20
Community Interactions
Also called: interspecific interactions
3 Basic Categories1. Competition2. Predation3. Symbioses
a) Parasitismb) Commensalismc) Mutualism
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Competition
Competition harms both species
Called a – / -- interaction
Competition is predicated on 2 concepts Competitive Exclusion Principle
When 2 species compete, 1 must lose & will be eliminated from the environment
1 species will always have an advantage Ecological niche
All of the biotic + abiotic resources that a species uses in its environment
Slide 5 of 20
Competitive Exclusion Principle
Gause studied paramecium
Discovered competitive exclusion principle Two (2) species cannot coexist in a community, if they occupy
the same niche For example, 2 paramecium species were studied, and one
was more fit than the other The result was that the less fit species was driven to
extinction
Competition between 2 species occupying the same niche can lead to 2 other options besides extinction, both involve some form of evolution
Slide 6 of 20
Niche
When species compete for resources, it is important to understand their niche
Niche – sum total of a species use of the biotic & abiotic resources in an environment Think of it as the species’ place in the ecosystem The roles (jobs) it occupies in an ecosystem
For example, a lion occupies the niche of predating (thinning?) herbivore populations
Another: HIV occupies the niche
Slide 7 of 20
2 Results of Competition
While extinction is possible, usually we get one of 2 situations due to competition for the same resource
1. Resource Partitioning – One species evolves to exploit different resources Different niche, but pretty close to the other species’
2. Character Displacement – divergence in body structure (via evolution) enabling access to different resources Darwin’s Finches beaks
Slide 8 of 20
-- Different Anoles (Lizards) predate the same populations, but in different parts of a wooded environment
Resource Partitioning
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Character Displacement
-- Finches evolved different beak depths, so they are able to eat different types of seeds
Slide 10 of 20
Predation
2nd type of interspecific interaction
Predatory Defenses include Cryptic coloration Aposematic (warning) coloration Batesian mimicry Mullerian mimicry Herbivorous defenses
Slide 11 of 20
Anti-Predation Defenses
Plants Physical defense mechanisms - spines/thorns Chemicals/Poisons – strychnine, mescaline, morphine,
nicotine
Animals Active defenses – hiding, fleeing or defending
themselves Passive defenses – Cryptic coloration or camouflage
Make it difficult for prey to be located
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Predation Defense Mechanism
Aposematic Coloration – bright coloration Typically orange or red Typically reserved for poisonous animals Visible warning to predator to stay away
Batesian Mimicry Copycat coloration Harmless animal copies the coloration of an animal that is poisonous
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2 or more poisonous species resemble each other and gain an advantage from their combined numbers
Predators quickly learn to avoid anything resembling this coloration
Mullerian Mimicry
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Symbioses
1. Parasitism (+/-)
-- Similar to predation (just takes longer)
-- Many ecologists link parasitism & predation
2. Commensalism (+/0)
-- Barnacles on a whale underbelly
3. Mutualism (+/+)
-- Bacteria inhabit GI tract & produce vitamins
Slide 16 of 20
Food Chain
Def – pathway by which food (energy) is transferred from one trophic (feeding) level to another
Energy moves from producers herbivores carnivores
10% of energy at any trophic level is transferred to the next level Because of this minority energy transfer, food chains are
limited to 4 or 5 trophic levels
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Trophic Pyramid
Primary Producers Green Plants Convert light energy to chemical bond energy Greatest biomass Diatoms & phytoplankton
Primary Consumer Herbivores Eats producers Grasshoppers
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Trophic Pyramid (Page 2)
Secondary Consumers Carnivores Eat primary consumers Frogs & small fish
Tertiary Consumers Carnivores Eat secondary consumers Top of the food chain Least biomass Hawk, salmon, & human
Slide 20 of 20
Food Chain (Page 2)
When considered in interrelation are called food webs An animal can occupy one trophic level in one food
chain, but a different trophic level in a different food chain
Example, a human is a primary consumer when eating vegetables, but a tertiary consumer when eating a salmon
Decomposers are usually not featured in trophic pyramids BUT they are integral to food chains & the circle of life
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