Community Ecology Chapter 54. Slide 2 of 20 Community Def. – group of populations (different...

Community Ecology

Chapter 54

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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

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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

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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

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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

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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

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-- 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

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Predation

2nd type of interspecific interaction

Predatory Defenses include Cryptic coloration Aposematic (warning) coloration Batesian mimicry Mullerian mimicry Herbivorous defenses

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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

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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

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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 (food) Pyramid

What % of energy is transferred to the next trophic level?

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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

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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

Community Ecology Chapter 54. Slide 2 of 20 Community Def. – group of populations (different...

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