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

Species Diversity• Communities are built around

a foundation species (one that stabilize environment)– Most often trees/plants

• One or two dominate species appear (majority of biomass)

• Species richness # of species present

• Relative abundance # in each species population

• Both together make Species Diversity greater the diversity the more stable the environment

Movement of Energy• Food Web showing all the

predator/prey connections in a community; made of all possible food chains

• Trophic levels where in the chain a species belongs– Primary producers all plant life and

photosynthesizers (autotrophs)– Primary consumers; herbivores

(heterotrophs)– Secondary consumers;

carnivores/omnivores• What is the most important group?• Recyclers Detritivores (animals

that eat dead material) and Decomposers (bacteria that eat dead material)

Complex Limits• If species richness and diversity

makes communities more stable, why is there not more diversity in nature?– Interspecific competition allows only a

small number of species to survive• What can fight against the selective

power of competition?– Predator/prey interactions

• Predators can keep prey in check that are competitors for other species

• Keystone species a species, that if removed, would have the most dramatic effect on a community’s structure

Dealing with Disturbances • A popular theory is that communities will

grow to equilibrium points and only shift when disturbances ruin their equilibrium

• An area experiences flooding after heavy rains throughout the year; r-selected or K-selected dominated?– r-selected; community change too often and

too quickly for K-species to adapt but r-selected can live their how life cycle between floods

• An area the experience little disturbances would be K-selected dominated; r-selected kept in check by K-selected predators

• What amount of disturbance creates the most diversity?– Intermediate disturbance hypothesis

common but mild disturbances allow mixing of r-selected factors but K-selected can still survive

Ecological Successions• Disturbances cause changes

(successions) in community composition• Primary Succession creating an

ecosystem from an area with no soil (after a volcano erupts or new land forms)

1) Lichens live on water and nutrients from rock bed; secret an acid which degrades rock into soil

2) Mosses live and die to build up nutrients

3) r-select plants (grass, ferns) move in and continue process

4) K-selected plants (trees) move in and allow large community to exist

• Climax community fully plant dominate community; stable until another disturbance comes

Other Successions• Disturbances like fire or

storms can cause a Secondary Succession

1) Disturbance removes large percent of plant community but rich soil remains

2) New species fill in spaces in community rapidly

• Aquatic Succession lakes and rivers fill in to become swamps; then rapid plant growth dries up area becoming a new meadow or forest

Are Successions Predictable • What determines how a community will

turn out as Successions occur?1) Facilitation hypothesis existing species

make the area more suitable for other species later on– Natural order to growth (lichens make soil for

mosses that build soil for plants)2) Inhibition hypothesis existing species

prevent new species from joining by filling their niche– No order; randomly based on which species

takes niche first3) Tolerance hypothesis inferior species are

replaced by superior ones – Competition decides as resources are limited

• Most likely a combination of all 3 and several other factors

Are Successions Predictable • Suggested Homework:– Test Your Knowledge

• Actual Homework:– Design an Experiment– Apply Evolutionary

Thinking– Due Thursday