II. Community Interactions(Chp 48) Def. “all the populations of organisms inhabiting a common environment and interacting with one another” Types of Interactions A.Competition 1.Competitive exclusion - when two species use the same limiting resource, one is always eliminated e.g. Paramecium caudatum and P. aurelia e.g. Paramecium caudatum and P. aurelia

2. Ecological niche - an organism’s role in the environment (its profession, not its address) a.Fundamental niche - determined by the physiological limits of the organism b. Realized niche - the portion of the fundamental niche actually utilized due to interactions with other species e.g. Chthamalus and Balanus barnaclese.g. Chthamalus and Balanus barnacles c. Niche Partitioning – closely related organisms that require the same resource will overlap little to to allow competing species to coexist e.g. five species of warblerse.g. five species of warblers

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B. Predation - eating of live organisms by animals, plants, or fungi 1. Population control 2.Increases species diversity - keystone predators maintain diversity by controlling the number of potentially dominant species i.Sea Stars (Pisaster) – control abundance of mussels and barnaclesSea Stars (Pisaster) ii.Periwinkles (snails) – control diversity of algal species

3. Drives evolution of predator and prey species a.Speed, strength, teeth, intelligence b.Defensive adaptations in plants i.Structures - thorns and spines ii.Chemicals - nicotine, morphine, strychnine (poison), and cinnamon, cloves, or peppermint (distasteful) c.Defensive adaptation in animals i.Concealment and camouflage - freezing, burrows, protective coloration, warning coloration, disguised appearance (walking stick, peppered moth, frog looking like bird dropping) ii.Disagreeable taste, odor, or spray - stink bug, monarch butterfly, bombardier beetle

Bombardier beetles (Brachinus spp.) inject an explosive mixture of hydroquinone, hydrogen peroxide plus several potent catalysts into a reaction chamber in the abdomen. Catalase breaks down the hydrogen peroxide into water and oxygen gas. Peroxidase oxidizes hydroquinone into benzoquinone. The mixture of chemicals and enzymes volatilizes instantly upon contact with the air, generating a puff of "smoke"" and an audible popping sound. This caustic flatulence is totally controlled by the beetle, otherwise it might accidentally blow up its rear end. The explosive discharge apparently discourages predators, either by chemical irritation, heat or repugnance. The temperature of the explosive mixture of gasses and fluids is over 100 degrees Celsius, the boiling point of water.

iii.Mullerian mimicry - using similar warning coloration e.g. Yellow jacket, sandwasp iv.Batesian mimicry - harmless species mimics unpalatable or dangerous species e.g. viceroy and monarch butterflies, flies and bees, hawkmoth larva and snake

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C. Symbiosis - close and long term association between two species, e.g. lichens = fungi + algae

1.Parasitism - one organism benefits, one is harmed - Plasmodium (malaria)-mosquito - tapeworm 2.Mutualism - beneficial to both organisms - nitrogen-fixing bacteria - PS algae in coral tissues - acacias and antsacacias and ants - protists in termite gut - mycorrhiza = roots and fungi - Leaf-cutter ant and fungusLeaf-cutter ant and fungus 3.Commensalism - beneficial to one, no effect on other (hitchhikers) - barnacles attached to whales - worm in sea cucumber's anus - clownfish and anemone