Community Ecology Chapter 54

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 Categories 1. Competition 2. Predation 3. Symbioses a) Parasitism b) Commensalism c) Mutualism

Slide 4 of 20 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 Different Anoles (Lizards) predate the same populations, but in different parts of a wooded environment Resource Partitioning

Slide 9 of 20 Character Displacement -- Finches evolved different beak depths, so they are able to eat different types of seeds

Slide 10 of 20 Predation  2 nd 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

Slide 12 of 20 Predation Defense Mechanism

Slide 13 of 20 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

Slide 14 of 20 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

Slide 15 of 20 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

Slide 17 of 20 Trophic (food) Pyramid What % of energy is transferred to the next trophic level?

Slide 18 of 20 Trophic Pyramid  Primary Producers  Green Plants  Convert light energy to chemical bond energy  Greatest biomass  Diatoms & phytoplankton  Primary Consumer  Herbivores  Eats producers  Grasshoppers

Slide 19 of 20 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