Population InteractionsCh. 51

Ecological Community • Interactions between all living

things in an area• Coevolution changes encourages

by interactions between two or more species– Predator vs. Prey– Herbivore vs. Plant

• Food Availability creates complex interactions:– Optimal Foraging Theory animal

must balance the energy spent to get food with the energy they get from eating it; determines diet

– Specialist eat one or few types– Generalist eat almost anything

Arms Race• Prey must adapt methods to

protect themselves if they are to survive– Hiding places; physical defenses;

poisons– Aposematic coloration bright,

contrasting color patterns that act as a warning of poison

• Predators must learn to over come these methods too– Recognize poisonous prey;

hunting skills; immunity to poisons

• Cryptic coloration camouflage to help hide predators and prey

Copy Cat• Mimicry resembling the

appearance of a another species to gain an advantage

• Batesian harmless species mimics a dangerous species – Mimic gains protection but

does not commit energy like the model does

• Mullerian dangerous species have similarities; predators learn of danger much faster

Fight for the Right to Survive• Interspecific competition competing

between different species– IntRAspecific competition inside a

population of one species1) Interference species directly limit

access to resources– Lions chase away hyenas

2) Exploitative species lower amount of resources so they are harder to find– Birds eat seeds so it is harder for

squirrels to find them• Competitive Exclusion Principle if

two population require the same limited resources in the same way, one will destroy the other

You Need a Niche• Niche specific way a species

interacts with its environment– All successful businesses need a

market in order to survive• Ecological niche the food

type, amount, and space required for a species to survive– Fundamental all possible

resources that CAN be used– Realized all possible resources

ACTUALLY used• Competition can occur when

fundamental niches overlap

Cant We All Just Get Along• Not all overlapping parts of niches

lead to competition– All animals breath air but rarely have to

compete for it• Resource partitioning different

species can use the same resources but can get them or use them in different ways– Birds species can feed on the same

insects but get them different parts of the tree

• Character Displacement– Sympatric species living in the same

area are more morphologically different• Darwin’s Finches

– Allopatric species living in different areas are less morphologically different

Symbiotic Interactions• Symbiosis physical ecological

interactions1) Commensalism one species benefits

and one species is not affected– Grass eaters stir up insects that birds will eat

2) Mutualism both species benefit– E. coli in your intestine gets nutrients from

us and gives us vitamins 3) Parasitism one species benefits

(parasite) and one species is negatively affected (host) – Tapeworm takes nutrition from our intestine

and decreases our health• Endoparasites live inside the body• Ectoparasites live outside the body

Defining A Community• Some see communities as “super-

organisms”; species in the community are so well connected they require each other to exist and to exist in certain amounts– Species composition could reach equilibrium

and shifts with major changes• Others think communities constantly

change and have no strict boundaries or composition

• Some biomes do have clear boundaries though; Water vs. Land, Aerobic vs. Anaerobic

• Ecotones edges where communities meet; full of biodiversity

• ESSAY!!!• Explain which of these ideas you most

agree with; support with reference material

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